Creep

Absrrucr-Our recent publication provided an assessment of the performance of thin porous gold in an office environment. We concluded that thin gold (0.380-0.75 pm) on printed wiring board (PWB) fingers provided acceptable performance primarily because of the benign nature of the office environment. Examination of samples with field life up to nine years also revealed the absence of the classical failure mechanism of pore and/or 'edge creep corrosion on about 20 000 plated surfaces examined. Work since that last paper leads us to believe that nickel oxide formation is the predominant degradation mechanism. For this reason, we chose the thermal aging test at 125°C to model field performance. Data at exposures of about 1500 h appear to approximate a field life of about ten years for copiers. Using thermal aging, we assessed the factors affecting the contact performance of thin gold. The interactive effect of connector characteristics, wear, and gold thicknesses was evaluated in unlubricated system. Gold thickness on PWB contact fingers ranged from O-l.0 pm over nickel underplating. For applications requiring 25 insert/ withdraw (I/W) cycles the factors affecting thin gold (0.380-0.750 pm) performance are 1) thickness determines the extent of wear, severity of underlayer exposure, and ultimately the extent of contact degradation, 2) wear on contact springs is more severe than on PWB fingers, 3) connector characteristics such as normal force, contact geometry, and gold thickness affect contact performance. A minimum of 0.380 pm of gold on PWB fingers is recommended. For applications with a lesser number of I/W requirements (<25), flash gold (0.10-0.25 pm) appears promising with two of the three connector types tested even though the finger surfaces appear eroded to the base underlayer. Gold dot (which is very thick) performed acceptably even up to 200 I/W. The advantage of lubrication on thin and flash gold is a logical extension of this study.

High-temperature creep tests were conducted on polycrystalline copper of commercial purity in order to investigate the inter-relationship between the extent and the rate of grain boundary sliding (GBS) and the development of internal cavitation. An image processing technique was used to provide quantitative information on the size and shape of the cavities formed over a range of stresses and at temperatures from 673 to 873 K. The results demonstrate that cavity development is inhomogeneous within any specimen, such that there is an increase in the level of cavitation in regions of higher local strain. It is shown by quantitative measurements that the total cavitated area increases at the faster sliding rates, but the number density of cavities decreases at the highest sliding rates because of cavity interlinkage. When interlinkage is taken into account, the results confirm that the overall level of cavitation is related to the occurrence of GBS.

Objective: To determine the effects of creep feeder design and feed accessibility on preweaning performance and the proportion of eaters of creep feed. Materials and methods: A total of 54 sows and their litters were assigned to three treatments: rotary feeder with hopper, rotary feeder without hopper, and pan feeder. A creep diet with 1.0% chromic oxide was offered ad libitum from Day 18 until weaning (Day 21). Fecal samples were collected from piglets with sterile swabs 3 to 12 hours before weaning. Piglets were categorized as "eaters" when either of the two fecal samples was colored green; otherwise, they were categorized as "non-eaters." Pigs were weighed Days 0 (birth), 18, and 21, and litter creep-feed disappearance was determined daily. Results: There were no differences (P > .05) in preweaning gains and weaning weights of pigs and litters using the different types of creep feeder. Litters provided creep feed using the rotary feeder with the hopper had 2.7 times lower total creep-feed disappearance than litters using the rotary feeder without the hopper and the pan feeder (P < .001). However, the rotary feeder with the hopper produced the highest proportion of pigs consuming creep feed within the litter (80%; P < .001). Implications: The proper choice of creep feeder is essential to manage creep feeding and to maximize the number of eaters in the litter. A creep feeder with a hopper may create more eaters with less feed wastage.

The purpose of this study is to evaluate the long-term vertical deformations of segmented pre-tensioned concrete bridges by a new approach. It provides a practical and reliable method for calculating the amount of long-term deformation based on creep and shrinkage in segmented prestress bridges. There are various relationships for estimating the creep and shrinkage of concrete. The analytical results of existing models can be very different, and the results are not reliable. In this paper, the different existing relationships are written in MATLAB software. After calculation, the values of the creep and shrinkage are stored. Then a sample bridge is simulated in the CSI-Bridge software, and different values of creep and shrinkage are allocated separately. Therefore, the data are analyzed, and its maximum deformation value is extracted at a critical span (Dv-max). Assigning different amount of creep and shrinkage to the model results in different values of Dv-max. In the next step, al...

A new popular method for retrofitting reinforced concrete beams is to bond fiber reinforced plastic (FRP) plates to the soffit. An important failure mode for such strengthened members is the debonding of the FRP plate from the member due to high interfacial stresses near the plate ends. As a result, previous researchers have developed several analytical methods to predict the interface performance of bonded repairs. In this paper, a theoretical interfacial stress analysis is presented, including creep and shrinkage effect for simply supported RC beams with a thin FRP composite plate. It explicitly considers the interface slip effect on the structural performance. The results agree reasonably well with those from the existing solutions. The influence of creep and shrinkage effect relative to the time of the casting and the time of the loading of the beams is taken into account. A parametric study has been conducted to investigate the sensitivity of interface behaviours to parameters such as the interface layer stiffness.

Nanostructuring metals through nanograins and nanotwins is an efficient strategy for strength increase as the mean free path of dislocations is reduced. Yet, nanostructures are thermally often not stable, so that the material properties deteriorate upon processing or during service. Here, we introduce a new strategy to stabilize nanotwins by an interfacial nanophase design and realize it in an interstitial high-entropy alloy (iHEA). We show that nanotwins in a carbon-containing FeMnCoCrNi iHEA can remain stable up to 900 °C. This is enabled by co-segregation of Cr and C to nanoscale 9R structures adjacent to incoherent nanotwin boundaries, transforming the 9R structures into elongated nano-carbides in equilibrium with the nanotwin boundaries. This nanoscale 9R structures assisted nano-carbide formation leads to an unprecedented thermal stability of nanotwins, enabling excellent combination of yield strength (~1.1 GPa) and ductility (~21%) after exposure to high temperature. Stimulating the formation of nano-sized 9R phases by deformation together with interstitial doping establishes a novel interfacial-nanophase design strategy. The resulting formation of nano-carbides at twin boundaries enables the development of strong, ductile and thermally stable bulk nanotwinned materials.

This paper introduces the numerical model analysis of evolutionary sections (AES) as a tool for the analysis of precast concrete sections constructed in several phases. Constitutive models including both concrete cracking and post-peak response of the materials were implemented. Likewise, the time-dependent behavior of the materials has been considered to model the sequential construction process. In order to validate the results obtained by the model, an experimental campaign (from the literature) was used. The comparison of the experimental results to those numerically obtained was satisfactory. The AES is already in use in several Spanish precast concrete factories for the optimization of bridges constructed with precast-prestressed concrete girders.

The Theta projection creep algorithm has been implemented within a finite element code. This extends the predictive capability of Theta projection data to complex geometries, multiple material problems such as welded joints, and non-steady temperature conditions. Validation of the finite element methodology has been undertaken by re-modelling creep data based on the original Theta coefficients. The stress redistribution in a cylindrical pressure vessel was examined and compared to that predicted by the Norton equation. The effects of temperature variation were also modelled. ᭧

The application of load cells in industry generally requires good basic materials and accurate performance in a wide range of environments. Differences exist in manufacturing technologies, intended application, performance and cost; however, hysteresis, frequency response and creep can be a common source of errors in standard strain gauge cells. In this paper, we present a small structure based on piezoresistive effect, implemented in Thick-Film Technology (TFT) on 96% alumina substrate, working as load cell with high resonance frequency and low creep effects. The analytic model has been verified by using simulation based on finite element methods (FEM), resulting in satisfactory agreement. Based on a figure of merit (the product of the sensitivity and the square of the resonant frequency), optimized design rules are obtained for the sensors of various measure-ranges from 1 N to 10 N.

Lifetime management of underground pipelines is mandatory for safe hydrocarbon transmission and distribution systems. The use of high-density polyethylene tubes subjected to internal pressure, external loading and environmental variations requires a reliability study in order to define the service limits and the optimal operating conditions. In service, the time-dependent phenomena, especially creep, take place during the pipe lifetime, leading to significant strength reduction. In this work, the reliability-based assessment of pipe lifetime models is carried out, in order to propose a probabilistic methodology for lifetime model selection and to determine the pipe safety levels as well as the most important parameters for pipeline reliability. This study is enhanced by parametric analysis on pipe configuration, gas pressure and operating temperature.

One of the largest long-runout landslides in the modern history of the Czech Republic originated on the southern slopes of the Girová Mountain (Outer Western Carpathians) at the end of extreme rainfalls in May 2010. The structurally predisposed Girová Mountain rockslide occurred very quickly within fault-weakened, deeply-weathered flysch bedrock. Its main phase, during which a wedge-like block collapsed in the upper part of slope, lasted for a few hours. The overloaded slope collapsed and its motion lasted for the following 3 days. The May 2010 Girová Mountain rockslide is an excellent case of a recurrent long-runout landslide nested within a deep-seated gravitational slope deformation with a long history of Late Quaternary mass movements. The chronology of slope failures within the studied slope was reconstructed by means of radiocarbon dating and dendrogeomorphological analysis. At least one Holocene long-runout landslide (7.4 cal ka BP) and several smaller failures (~1.5 and~0.6 cal ka BP) preceded this recent catastrophic failure. Dendrogeomorphological analysis showed that the failure had been preceded by at least 80-year-long creep movement that accelerated over the years due to extreme rainfall events. Despite the fact that extreme precipitation of May 2010 represented the last incremental change before catastrophic collapse of the slope, its main reason was gradual weakening of rock massif and concentrated creeping (with some accelerated phases) in the upper part of the slope deformation.

The creep of a dislocation on its glide plane is essentially controlled by three different stress fields: the external applied stress, the internal stress field due to a multi-scale hierarchy of different obstacles (the structural defects acting on the dislocation by short-or long-range interactions) and the thermal stress field due to thermal fluctuations. The dislocation glide dynamics involves solution of a string equation, which can be written as a Langevin equation. In this paper, it is shown that general analytical solutions of this equation can be found, allowing calculation of the plastic strain rate and the amplitude-dependent internal friction (ADIF), by using simple assumptions concerning the multi-scale hierarchy of obstacles and the mechanisms of Brownian dislocation creep through the different kinds of interacting obstacles. It is also shown that several experimental observations are well explained by this approach.

A life assessment of a hot reheat bifurcation has been undertaken. Surface breaking cracklike indications were detected in the bifurcation weld. Subsequent replication showed that this was due to significant creep damage in a number of material zones within the weld. This damage was removed by hand dressing until it had been reduced to an acceptable level below which good material remained with minimal damage; this was confirmed by additional replication. A finite element analysis was undertaken based on the elastic rupture reference stress multiplied by weld redistribution factors which quantifies stress redistribution within the weldments. The results indicated that creep damage would be evident on both the external surface of the saddle region and on the inside surface at the crotch position. Additional analysis based on a RIKS procedure and an elastic-perfectly plastic analysis confirmed the results of the rupture reference method. A full re-inspection of the bifurcation branch was recommended before another 10,000 h of service was completed as a consequence of this study. At the next inspection recurrence of the damage was found, and internal inspection confirmed the analysis results with damage also present on the internal surface at the crotch position. Based on these findings replacement of the bifurcation has been recommended.

We investigated the deformational behavior of fine-grained calcite-anhydrite aggregates at conditions where the end-member phases are of similar strength and deform by dislocation creep and/or difømsion creep • ' • various---' p• Ulamdun• w• • m,m• by .,,, ,o,,o,,, ..... : pressing CaCO3 and CaSO4 powders into dense aggregates. Grain sizes are 5 and 8 gm for two different anhydrites (An) and 8 gm for calcite (Cc). In all mixtures, grain sizes are 2-4 gm for both phases. The stress difference c•, strain rate • and grain size d data are fit to a power law with g o• o •. At 500øC, grain flattening accounts for most of the sample strain for all mixtures,

This paper presents the modelling of the 3D motion of a piezo-actuated tunneling tip in an STM-like (Scanning Tunneling Microscope) micromechanical system, with the aim of summarizing challenging control problems in such a nanoscale device and developing a control strategy accordingly. Those control problems are settled with a purpose of surface reconstruction. To do so, various adverse phenomena like tunneling nonlinearity, actuator hysteresis, creep, vibrations and crosscouplings are compensated. A multivariable Linear Quadratic Integral (LQI) control is proposed, together with a Kalman observer for surface reconstruction, which are shown to provide improved performances in comparison with a more classical Single-Input Single-Output (SISO) control approach.

The predominance of phenomenological power laws in creep of crystalline materials indicates that the dislocation mechanics of inelastic deformation of crystalline materials has not yet been fully understood. We review the progress towards a general and comprehensive model. In general, dislocation-mediated plasticity leads to generation of dislocations in the crystal interior. Creep, i.e. plasticity at constant stress, continues only if dislocations are able to disappear again (dislocation recovery). A simple model of creep of subgrain-free materials reproduces characteristic features of steady-state creep, but shows significant quantitative deficiencies, indicating that subgrain formation must not be neglected. It is proposed that migration of low-angle subgrain boundaries constitutes the process controlling creep in most cases of single-and multi-phase materials with conventional grain size. High-angle boundaries begin to play a significant role when their spacing d approaches the steady-state subgrain size w ∞ developing in coarsegrained materials. Depending on the w ∞ /d-ratio and deformation conditions, high-angle boundaries may harden or soften the material in the steady state of deformation.

The oxidation characteristics of Alloy617, a candidate structural material for the key components in the very high temperature gas-cooled reactor (VHTR) application, were investigated. High temperature oxidation tests were conducted at 900 o C and 1100 o C in air and helium environments and the results were analyzed.

We report on creep and stress relaxation test results for pure polycrystalline magnesium. The experiments consisted of constant load creep tests conducted until steady-state was obtained followed by stress relaxation tests to study the strain-hardening and recovery behaviour of the materials. The tests were carried out over a range of applied stresses, 20-50 MPa, and test temperatures, 150-250°C, in order to determine stress and temperature dependencies of the high temperature plastic deformation behaviour. The strain-hardening coefficient, H, is derived from the experimentally generated steady-state creep rate, ~s, and the dynamic recovery rate, R, data by using the well-known Baileyq:)rowan relationship. It is found that the strain-hardening coefficient, H, during steady-state creep remains essentially constant with a magnitude of 0.27E (E is the elastic modulus) at 200°C and is independent of the applied stress. The creep strain rate is primarily determined by the recovery rate which is the rate determining mechanism during recovery creep. This set of experimental results is then examined in terms of creep equations and the dislocation network models for recovery creep deformation. It is shown that the present experimental data measured for pure polycrystalline magnesium lend support to the theoretical models based on dislocation link length distribution (dislocation network models) for recovery creep.

Microelectronic encapsulants exhibit evolving properties that change significantly with environmental exposures such as isothermal aging and thermal cycling. Such aging effects are exacerbated at higher temperatures typical of thermal cycling qualification tests for harsh environment electronic packaging. In this work, the material behavior changes occurring in flip chip underfill encapsulants (silica filled epoxies) have been characterized for isothermal aging at four different temperatures that are below, near, and above the T g of the material. A microscale tension-torsion testing machine has been used to evaluate the uniaxial tensile stress-strain and creep behaviors of the underfill material at several temperatures, after various durations of environmental exposure. A novel method has been developed to fabricate underfill uniaxial test specimens so that they accurately reflect the encapsulant layer present in flip chip assemblies. Using the developed specimen preparation procedure, samples were prepared and isothermal aged for up to 6 months at 80, 100, 125, and 150 qC. Stress-strain and creep tests were then performed on both non-aged and aged samples at several different temperatures (25, 50, 75, 100, 125, and 150 o C). The changes in mechanical behavior were recorded for the various aging temperatures and durations of isothermal exposure.

Published accounts of peat mass movements throughout the last 500 years reveal common characteristics among the failures; however, there has been no consistency in the terminology used to describe them. Given the apparently increasing frequency of peat failures in the British Isles and the possibility of more peat failures elsewhere in the world as a consequence of climate change, there is a need for a specific classification scheme. This paper proposes a scheme that uses clearly defined terms that can be readily applied and reliably used to understand and assess future hazards from peat mass movements. The paper begins with a general definition of what should constitute a ‘peat failure’, then presents a precisely defined classification scheme for peat landslides (i.e. excluding creep), using type of peat deposit and failure morphology as the key criteria. The new scheme for peat failures is discussed in the context of existing landslide classification systems. Definitions are provided for bog bursts (flow failure of raised bogs), bogflows (flow failure of blanket bogs), bog slides (shear failure and sliding of blanket bogs), peat slides (shear failure at peat–mineral interface in blanket bogs), peaty-debris slides (shear failure within mineral substrate beneath blanket bogs) and peat flows (natural failures of other types of peat deposits including flow failure caused by head-loading). Some practical problems of classifying peat failures are discussed.

The future success of many electronics companies will depend to a large extent on their ability to initiate techniques that bring schedules, performance, tests, support, production, life-cycle-costs, reliability prediction and quality control into the earliest stages of the product creation process. Earlier papers [1, 2] have discussed the benefits of an integrated analysis environment for system-level thermal, stress and EMC prediction. This paper focuses on developments made to the stress analysis module and presents results obtained for an SMT resistor. Lifetime predictions are made using the Coffin-Manson equation. Comparison with the creep strain energy based models of Darveaux [3] shows the shear strain based method to underestimate the solder joint life.

Creep behavior of neat, talc-filled, and short glass fiber reinforced injection molded thermoplastic composites were investigated and modeled at room and elevated temperatures. Creep strength decreased and both creep strain and creep rate increased with increasing temperature. The temperature effect was more significant for samples with glass fibers in the transverse to the load direction, as compared with the longitudinal direction. The LarsoneMiller parameter was able to correlate the creep rupture data of all materials. The MonkmaneGrant relation and its modification were successfully used to correlate minimum creep rate, time to rupture, and strain at rupture data. The Findley power law and timeestress superposition principle (TSS) were used to represent nonlinear viscoelastic creep curves. Long-term creep behavior was also satisfactory predicted based on short-term test data using the TSS principle.

Ingenieurwerkstoffe neigen bei erh€ o ohten Temperaturen zus€ a atzlich zum elastischen Verhalten zum Kriechen oder, mit anderen Worten, man kann neben einer spontanen Werkstoffreaktion auch eine zeitabh€ a angige beobachten. Unter Ber€ u ucksichtigung der wachsenden Sicherheitsanforderungen f€ u ur Kraftwerke, Flugzeugkomponenten, chemischen Anlagen usw. ist das zeitabh€ a angige Werkstoffverhalten in den Konstruktionsprozess einzubeziehen. Zahlreiche Bauteile, die unter Kriechbedingungen eingesetzt werden, k€ o onnen als d€ u unnwandig klassifiziert werden. Ihre Analyse ist dann mit drei Problemen verbunden: mit der Auswahl eines geeigneten Werkstoffmodells, mit der Auswahl eines ad€ a aquaten strukturmechanischen Modells und mit der Auswahl eines geeigneten numerischen L€ o osungsverfahrens. Dabei besteht eine enge Verbindung zwischen den drei Problemen. Beispielsweise hat die Auswahl des strukturmechanischen Modells (Balken, Platte, Schale usw.) signifikanten Einfluss auf den numerischen Aufwand. Andererseits wird die Berechnungsgenauigkeit durch das Materialverhaltensmodell beeinflusst, wenn verschiedene Effekte einbezogen oder vernachl€ a assigt werden. Die Kriechmechanik als Zweig der Festk€ o orpermechanik hat eine mehr als einhundertj€ a ahrige Geschichte. Nach einer kurzen Diskussion der geschichtlichen Entwicklung sowie der Anf€ u uhrung ausgew€ a ahlter Referenzliteratur werden zwei Modelle zur Beschreibung des Kriechverhaltens eingef€ u uhrt. Das erste Modell ist dadurch gekennzeichnet, dass die Art des Spannungszustandes keine Rolle bei der Beschreibung des Materialverhaltens spielt, w€ a ahrend in die Formulierung des zweiten Modells eine derartige Abh€ a angigkeit eingeht. Ein typisches Beispiel f€ u ur das zweite Modell ist ein unterschiedliches Zugund Druckverhalten. Dieses kann beispielsweise im Terti€ a arkriechbereich vorausgesetzt werden, da eine Sch€ a adigung durch Zugbedingungen gef€ o ordert wird. Wenn man Druckbedingungen antrifft, k€ o onnen Kriechverzerrungen auftreten, der Sch€ a adigungszustand ist jedoch teilweise eingefroren (u.a. kein Auftreten neuer Hohlr€ a aume). Der letzte Teil ist strukturmechanischen Modellen gewidmet. F€ u ur d€ u unnwandige Strukturen werden in der Regel alle Annahmen in € U Ubereinstimmung mit der ,,D€ u unne'' der Struktur getroffen. Damit kann man beispielsweise Hypothesen f€ u ur die Spannungen, Verzerrungen und/oder Verschiebungen in Dickenrichtung einf€ u uhren, und es werden zu l€ o osende Gleichungen abgeleitet, die bez€ u uglich der Dimension reduziert sind (statt dreidimensionaler Feldgleichungen hat man ein System von zwei-oder eindimensionalen Feldgleichungen). € U Uber die Korrektheit und Genauigkeit dieses Konzepts wird berichtet.

this paper proposes a method for determining Burger's model parameters using creep-recovery data. With the determined Burger's model parameters, the viscoelastic behaviors of an asphalt binder (PG64-28) and its two mastics (a binder PG64-28 blended with mineral fines passing the ASTM 100# sieve and 200# sieve, respectively) are investigated. The total deformation of the mastics was separated into three parts: the instantaneous elasticity, delayed elasticity, and viscous flow. The ratios of the viscous flow to the elasticity were calculated and analyzed. It was found the proposed method is promising where the average errors of the creep section are 3.53%, 5.28% and 8.02% for the three materials, and the errors in the recovery section are 0.69%, 1.286% and 1.80%, , respectively.

This paper presents a new constitutive model describing the mechanical behavior of concrete at early age and beyond. This model, entitled solidification-microprestress-microplane (SMM) model, amalgamates the microplane model and the solidification-microprestress theory and takes into account all the most significant aspects of concrete behavior, such as creep, shrinkage, thermal deformation, and cracking starting from the initial stages of curing up to several years of age. Age-dependent viscoelastic behavior under variable hygro-thermal conditions is described according to the solidification-microprestress theory. Cracking/damage behavior is modeled through an age-dependent microplane model, in which the model parameters are assumed to be dependent on an aging variable evolving with the extent of early-age chemical reactions (hydration, silica-fume reaction, etc.) and temperature. Calibration and validation of the model is performed by the numerical simulations of the age-dependent response of sealed and unsealed specimens subject to a variety of loading conditions and/or drying. Comparison with experimental data shows that the SMM model can reproduce well the interplay of shrinkage, creep, and cracking phenomena during curing and drying.

Polyethylene-based heavy-duty shipping sacks are used around the world to package and ship products such as soil, fertilizer, mulch, gravel, and pelletized resin. Approximately 1000 kilotons (kt) of polyethylene is converted into heavy-duty sacks annually around the world. Previously, ExxonMobil Chemical Company analyzed a variety of heavy-duty sacks and found sacks made from m-LLDPE blends and co-extruded films exhibit a superior balance of mechanical, optical and sealing properties versus traditional Zeigler-Natta resins. Now, EMCC has taken this performance a step further. e J J e J t J

There are several reasons for mechanical stresses in "globbed" assemblies. For example: cure shrinkage; thermal gradients; and moisture diffusion. Thermal mismatch between substrate, silicon die, and encapsulant represent a main reason for thermally induced stresses and is investigated in detail. The filled polymers used have shown temperature, time, and moisture dependent mechanical characteristics. The viscoelastic properties of the encapsulant below the glass transition temperature (T g ) are represented by a Prony series sum of exponentials with three terms, while the temperature dependence is included by a temperature time shift formula. Finite element (FE)-simulations including the creep characteristics allow the evaluation of thermally induced stresses. The calculations show the major stress concentration to occur at the inner edge between die/adhesive/encapsulation and the ceramic board. Local stress concentrations arise at the upper interfacial edge die/encapsulation and at the outer border of the glob-top. Furthermore, the theoretical results are compared with observations of thermally cycled hybrids made by scanning acoustic microscopy (SAM) and metallographic investigations. In this way not only the influence of thermal cycling, but also humidity exposure on the glob-top's integrity was evaluated. The typical failures were shown to be delaminations at the epoxy encapsulant interface.

A creep-fatigue test with a structural specimen made of Mod. 9Cr-1Mo steel and 316L stainless steel has been carried out and the test results were compared with those of the evaluations by the high temperature design codes of ASME subsection NH and RCC-MR to quantify the conservatism. A specimen with a diameter of 500 mm, height of 440 mm and thickness of 6.3 mm was subjected to creepfatigue loads with two hours of a hold time at 600°C and a primary nominal stress of 30 MPa. The creep-fatigue behaviours of the dissimilar metal welds as well as the similar metal welds were investigated and the results of the test were compared with the evaluation results. Bimetallic (direct) transition metal joint and trimetallic transition metal joint for a dissimilar metal weld were employed for a specimen, and their behaviours under a creep-fatigue load were compared. The conservatism of the design codes on the creep-fatigue evaluation at the welded joints as well as at the base metal with an emphasis on Mod.9Cr-1Mo steel are highlighted through comparisons with the results from the observation and the evaluation.

La historia que inspiro la saga camino hacia el terror. Hola estimados suscriptores, amantes de lo oscuro y las leyendas urbanas, ¿cómo ha estado su familia? En esta ocasión les hablaremos de la historia que inspiró a la saga de películas Camino hacia el terror. Sawney Beane; miembro de una familia granjera a lo cerca de Edimburgo, frente a la costa oeste de Escocia, en determinado tiempo ya para finalizar el siglo dieciséis. Éste, en compañía de su esposa, deja la granja donde nació, siendo muy joven e inicia su viaje para la contraparte del país. Cuando iban por el camino toman la decisión de vivir en una profunda cueva, al parecer estos sujetos eran aventureros. El lugar para entrar era un pequeño hueco y mientras se caminaba hacia dentro más grande se iba haciendo la caverna. Se estima que su longitud era de alrededor de una milla. Y durante veinticinco años, la nueva familia Beane la tomó como su casa para vivir de forma indefinida. Por todo este tiempo estuvieron viviendo a expensas de los transeúntes, viajeros ignorantes de lo que estaba por acontecerles. En sus inicios vivían de las cosas que les quitaban y para no ser descubiertos, los mataban después de haberlos asaltado. Ya en lo sólo, fuera de todo contacto social, más que con las víctimas que pasaban por donde se encontraban, perdieron la vergüenza e iniciaron la práctica del incesto. Después de 25 años, la familia ya tenía nietos, mismos que participaban en los actos de intimidad. Como ya eran bastante, sus necesidades y el poco pudor empujaron a esta fructífera familia a iniciarse en la antropofagia. Empezando a comerse a las personas victimizadas. Se los llevaban a la cueva donde todos los familiares se daban un festín, haciéndose aficionados a la carne humana. En las formaciones rocosas de Galloway, durante esos veinticinco años les hicieron ver el infierno en vida a los poco afortunados viajeros. Únicamente, lo que se hallaban de las personas desaparecidas, eran las sobras que tiraban al mar y la corriente las hacía llegar a las costas de Escocia. Pellejos que ni los animales querían y mucho menos los huesos habiendo carne. Varias teorías por los despojos y desechos encontrados a las orillas del mar fueron suscitadas. manuelverdugo.com

Mechanical properties of solder masks are critical in the reliability performance of flip-chip packages. Many recent studies show that the mechanical properties of solder mask materials have great influence on moisture absorption, delamination at interconnections and solder fatigue life in flipchip packages. There are also assembly process issues related to the properties of solder masks. In this article, an experimental investigation that mechanically characterizes solder one mask material is conducted. Mechanical properties such as Young's modulus, failure strength and creep behaviors are determined based on the measured data from the experiments. The testing temperature is set at two levels: 25OC and 8OOC. The major instrument is a sophisticated micro mechanical tester.

This paper reports on the measured wheel-rail creep force characteristics and the mechanism of corrugation formation by using a full-scale bogie on a test stand. The measured creep characteristics agree well with the calculated values based on Kalker's linear theory. The relationship between creep characteristics and contact position is also discussed. The results show that a small change in wheelset lateral displacement may lead to a great change in creep characteristics. Mathematical models are developed in order to explain the mechanism of corrugation development. Simulation results agree well with practical phenomena. From the simulation results we find that the creep force characteristics and the vertical oscillation system have great influence on the formation mechanism of rail head corrugation.

Reliability centered maintenance (RCM) has a key role in the quality system of thermal power plants. Electricity production is definitely not only production of a product, but also becomes a customer service. Reliability is the top quality tier of this service. Incorporation in the Integrated energy system means fast transformations of organization on all levels. The reliability of modern generation components basically influences the efficiency and capacity of a power plant as a whole. This paper presents the results of RCM practice on Unit Two of The Thermal Power Plant ″Nikola Tesla -B″, 2x600 MW, Yugoslavia. RCM implementation on current problems during exploitation emphasized problems with the boiler tubing system. The methodological approach included outages analyses, marking of the most significant ones, determination of main causes of damage (determination of the material exhaustion state based on expert analyses), application of adequate remaining life assessment methodology and finally the recommendations. Based on these analyses, certain technical solutions were performed and as a result, the mean time between failures of the plant increased, as well as its reliability. According to cost efficiency, RCM methodology presented the most effective cost-benefit method for reliability upgrade.

The general area of physical aging of polymers is reviewed. Various phenomenological aspects are introduced and discussed in terms of bulk structural changes evidenced by dilatometric and calorimetric studies, and are compared with the wide variety of information available from microstructural investigations involving spectroscopic and scattering techniques. Current models for describing the relaxation kinetics of the non-equilibrium glassy state are compared. Finally, the effects of physical aging on mechanical properties are reviewed, highlighting especially those areas which remain controversial.

The present study investigates the potential use of high-density polyethylene (HDPE) on performance characteristics of asphalt mixtures such as fatigue cracking and rutting as major distresses of hot mix asphalt (HMA). In order to assess the impact of HDPE as an asphalt binder modifier on the behaviour of HMA, control mixes without HDPE and mixes containing HDPE in dry and wet conditions were tested. The results show that fatigue life is higher in mixtures containing HDPE than those for control mix. Also, HDPE-modified mixtures provide better resistance to rutting due to their higher stiffness. In addition, by increasing the temperature and fatigue life, resistance to permanent deformation of all specimens decreased, where sensitivity to temperature is lower in mixes containing HDPE. On the other hand, results of the laboratory tests indicate that HDPE increases the adhesion between the asphalt binder and the aggregate in the presence of moisture.

This review article concerning natural and man-made cellulose fibre reinforced plastics, introduces possible applications of this material group. The physical properties of natural fibres are mainly determined by the chemical and physical composition, such as the structure of fibres, cellulose content, angle of fibrils, cross-section, and by the degree of polymerization. Only a few characteristic values, but especially the specific mechanical properties, can reach comparable values of traditional reinforcing fibres. This physical structure can be modified by using alkali treatment and acetylation processes. The application of natural fibres as reinforcements in composite materials requires, just as for glass-fibre reinforced composites, a strong adhesion between the fibre and the matrix, regardless of whether a traditional polymer (thermoplastics or thermosets) matrix, a biodegradable polymer matrix or cement is used. Further this article gives a survey about physical and chemical treatment methods which improve the fibre matrix adhesion, their results and effects on the physical properties of composites. These different treatments change among others the hydrophilic character of the natural fibres, so that moisture effects in the composite are reduced. To bring about hydrophobic properties to natural fibres, a special treatment, termed acetylation, can be used. The effectiveness of this method is strongly influenced by the treatment conditions used. The mechanical and other physical properties of the composite are generally dependent on the fibre content, which also determines the possible amount of coupling agents in the composite. The influence of such treatments by taking into account fibre content on the creep, quasi-static, cyclic dynamic and impact behaviour of natural fibre reinforced plastics are discussed in detail. For special performance requirements, hybrid composites made of natural and conventional fibres can be prepared with desired properties. The processing conditions play, next to the mechanical properties of natural fibres, an important role for the industrial use of these materials. The results presented in this paper show, that natural fibres can be processed with the already commonly applied methods: glass mat thermoplastic matrix (GMT), sheet moulding compound (SMC) or bulk moulding compound (BMC). For the processing of thermoplastics reinforced with natural fibres, new methods (e.g. the ''EXPRESS'' processing) are of increasing importance. Natural fibres seem to have little resistance towards environmental influences. This can be recognized in the composite and can be advantageously utilized for the development of biological degradable composites with good physical properties. ᭧ Fig. 7. Influence of MAH-PP treatment conditions on the modulus of jute-fibre reinforced polypropylene (fibre content 30 vol.%) [67].

A B S T R A C T Polymer composites are suitable alternatives to metals in some applications as they are cost effective, lightweight and corrosion resistant. Short fibre reinforced polymer composites (SFRPCs) are typically subjected to complex loadings in applications, including static, cyclic, thermal and their combinations. These applications may also involve harsh environmental conditions such as elevated temperature and moisture which can dramatically affect mechanical properties. In this paper, a broad survey of the literature on mechanical behaviour of SFRPCs at elevated temperatures is presented. The mechanical behaviours included consist of tensile, creep, isothermal fatigue, thermo-mechanical fatigue and creep-fatigue interaction. Environmental effects such as moisture and ageing at elevated temperatures are also included. The studies reviewed include experimental works, modelling works and failure mechanisms studies. A critical assessment of the information from the literature presented for each type of behaviour is also provided.

Due to the empirical nature and the drawbacks of the Marshall mix design procedure, the Strategic Highway Research Program (SHRP) has developed a Superior Performance asphalt Pavements (SUPERPAVE) mix design procedure. In this research a comprehensive evaluation of the locally available aggregate usually used in the asphalt concrete mixtures was carried out to ensure that these materials conform to the new mix design procedures developed by SUPERPAVE. A performance grading map was generated to the Hashemite Kingdom of Jordan. In this map the country was divided into different zones according to the highest and lowest temperature ranges that the asphalt might be subjected to. Using local materials, loading and environmental conditions, a comparative study of the performance of two mixes designed using SUPERPAVE and Marshall mix design procedures was carried out in this research. Samples from both mixes were prepared at the design asphalt contents and aggregate gradations and were subjected to a comprehensive mechanical evaluation testing. These tests included Marshall Stability, Loss of Marshall Stability, Indirect Tensile Strength, Loss of Indirect Tensile Strength, Resilient Modulus, Fatigue Life, Rutting, and Creep. In all the performed tests SUPERPAVE mixes proved their superiority over Marshall mixes. Therefore, serious plans should be set up in Jordan to shift from the presently used Marshall mix design procedure to SUPERPAVE mixture specifications.

In the current scenario of power shortage in India, the main objective is to ensure availability of power plant and increasing its reliability. During assessment ,testing and inspection a simple question has to be asked again and again‖ How long the particular power plants can be operated safely and cost-effectively with satisfying increased requirements and operational availability with reduced pollutant emissions, even after their designed life. So to answer this important question regarding the operational capability of the existing plant the remaining life analysis (RLA) has to be done. The condition of the plant equipments can be assessed only by way of a RLA methodology. On the basis of RLA proper decision can be made about the plants safety and availability. There are many methods to carry out the RLA of the critical components out of which -microstructure study‖ is a method. In this paper we have tried to outline the RLA procedures and review the various damage mechanisms based on microstructure study. It is also presents the microstructure changes and properties of 106720 service hour exposed boiler tube in a 120 MW boiler of a thermal power plant.

The crankshaft is an essential component of internal combustion engines, which is widely used in an automobile. The most common modes of crankshaft failure are fatigue failure. During its operation, the crankshaft is always subjected to a cyclical load. Besides, the bending and shear load are also typical loads on the crankshaft. Due to the effect of these loads, the crankshaft fails and causes a substantial economic and loss of life. Therefore, predicting the more accurate fatigue life of the crankshaft is essential to save the economic and life losses. This paper discusses several existing approaches to predicting crankshaft fatigue life. Various analytical and experimental approaches used to predict fatigue life discussed. The most common analytical approaches used to predict life are total life approaches, crack initiation life prediction approaches, and crack growth. The review shows that most crankshaft failures are the result of fatigue. The crack initiation can occur due to high-stress concentration or as a defect during manufacture and can eventually propagate under cyclic loads.

In the petrochemical and nuclear industries, the difficulty in assessing the effect of creep on the tightening load of bolted flanged connections is recognized. Under high temperatures, the leak tightness of bolted joints is compromised due to the loss of the bolt load as a result of creep of not only the gasket and bolt materials but also the flange material. Apart from acknowledgment of this effect, there exists no established design calculation procedure that accounts for creep. This is because the relaxation of the bolt load and the corresponding loss of the gasket contact stress are not easy to assess analytically. The main objective of the work is the development of a simple analytical solution to the creep-relaxation problem encountered in bolted flange connections of the float type. Particular emphasis is put towards relaxation caused by the flange and bolt material creep.

Three published rock mass classi®cation systems (RMR, SMR, RMS) were applied to weak Waikato Coal Measure mudrocks in order to assess their value as indicators of rock mass conditions and stable slope angles. The SMR classi®cation gives the most sensitive measure of rock mass conditions for the slopes studied, but none of the systems adequately predicts observed slope angles. Regression analysis indicates that where conditions for failure by sliding along discontinuities exist the slopes are most sensitive to the discontinuity parameters of parallelism, dip angle and spacing. Further, when the discontinuities are oriented favourably with respect to the slope, slope angles are most sensitive to intact rock strength and groundwater. This is supported by geomorphic evidence. Low angle natural slopes developed on unfavourable discontinuity sets are well predicted by published equations associated with both the RMR and RMS classi®cation systems. Steeper slopes developed on favourable discontinuities are at a much lower angle than the equations predict and show evidence of extensive creep. Application of the present rock mass classi®cation systems to these weak rocks is thus only appropriate when conditions exist under which the rocks fail by sliding on unfavourably oriented discontinuities. Where this does not occur, the contribution of intact strength to the rock mass strength is greatly overestimated by all of the rock mass classi®cation systems studied. Development of a separate rock mass classi®cation for these conditions is not seen as appropriate. Hence, recognition of the favourability or otherwise of the discontinuity sets is crucial to dealing with these rocks. A stereonet overlay that facilitates this division is presented. q