Creep

El Hormigón Reforzado con Fibras (HRF) es un material de alta performance que se destaca por su capacidad de controlar la formación y propagación de fisuras y por su mayor tenacidad, lo que redunda en mejoras la vida en servicio de las construcciones. Si bien hace más de cuatro décadas que se conoce al HRF, en los últimos años se realizaron grandes avances en la materia que abren enormes perspectivas para su mayor aprovechamiento en la ingeniería, los cuales son puntualizados brevemente en este artículo.Fil: Zerbino, Raul Luis. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Construcciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Creep behavior of cracked fiber reinforced concrete is analyzed in service conditions. Different stress levels and pre-cracking damages are considered. Creep does not generate negative effects on the residual post-creep behavior. Crack Opening Rate depends on both pre-cracking damage and applied stress level. An expression to predict Crack Opening Rate values is proposed.

Many researchers have proposed equivalence betwee or similar time-temperature parameter approaches. T testing as compared to the long-time creep tests. B behavior controlling both the hot-tensile and creep p significant changes for the time periods under co development and preliminary screening. Such a tim predicting the stress-rupture behavior of 316 L(N) s compared with actual creep test data for almost a sim the ASME Code Case minimum stress-rupture data creep rates are also much larger than the actual one drawn is that considering the microstructural stabilit contents), the method of equivalence of hot-tensile an rates, rather than the single value considered here, results. In addition, using some old results from th nitrogen content and grain-size for the present heats o

Prestressed segmentally constructed balanced cantilever bridges are often subjected to larger deflections than those predicted by calculations, especially for long-term effects. In this paper, the case of modular balanced cantilever bridges, which are prestressed segmental bridges obtained through a repetition of the same double cantilever, is investigated. The considered bridges are two typical cases of modular balanced cantilever both subjected to large deformations during their lifetime. In this case, due to the unusual employed static scheme, creep deflections indefinitely evolve over time particularly at the end of the cantilevers and in correspondence with the central joint. These remarkable deflections cause discomfort for vehicular traffic and in certain cases can lead to the bridge collapse. Important extraordinary maintenance interventions were necessary to restore the viability of the bridges and to replace the viaduct design configuration. To this aim, the static schemes...

Sensitivity study on material properties for the fatigue life prediction of solder joints under cyclic thermal loading A computational study is presented in this paper to investigate the effect of variation in material properties on the fatigue life prediction of solder joints subjected to cyclic thermal loading. The package under investigation was a plastic quad flat pack (PQFP) with gull-wing leads. A commercial finite element code, ABAQUS, was employed to perform a two-dimensional plane stress analysis. While all other constituents of the PQFP assembly were assumed to be linear elastic, the solder joint was considered to be elastic-viscoplastic. The creep model was adopted from Norton's equation and was implemented in the finite element analysis via a user-defined subroutine. The maximum creep strain was evaluated and incorporated into the modified Coffin-Manson equation to estimate the life cycles under thermal fatigue. It was found that the variation in material properties could have a significant influence on the fatigue life prediction of solder joints.

A computational study is presented in this paper to investigate the effect of variation in material properties on the fatigue life prediction of solder joints subjected to cyclic thermal loading. The package under investigation was a plastic quad flat pack (PQFP) with gull‐wing leads. A commercial finite element code, ABAQUS, was employed to perform a two‐dimensional plane stress analysis. While all other constituents of the PQFP assembly were assumed to be linear elastic, the solder joint was considered to be elastic‐viscoplastic. The creep model was adopted from Norton’s equation and was implemented in the finite element analysis via a user‐defined subroutine. The maximum creep strain was evaluated and incorporated into the modified Coffin‐Manson equation to estimate the life cycles under thermal fatigue. It was found that the variation in material properties could have a significant influence on the fatigue life prediction of solder joints.

The incorporation of natural fibers into polymer matrices poses challenges due to physicochemical incompatibility, which is typically addressed through precursor modification or the use of compatibilizers. Here, we introduce a novel type of composite that overcomes this challenge by utilizing a network of fine, porous cellulosic sheets inter-diffused with a commercial paraffin films. This approach physically adheres the fiber network to the matrix, preserving its structure. Microscopy images confirm the formation of the proposed microstructure, and mechanical testing reveals a gradual increase in modulus and strength with the incorporation of cellulose. The maximum incorporation achieved was 7.6% (w/w) of cellulosic fibers, resulting in a 167% increase (1.67 times improved) in composite stiffness. Moreover, these composites exhibit ductility, with an average deformation of 410 ± 38%, corresponding to 20% reduction in relation to pure matrix. Our findings demonstrate the potential of this approach for developing sustainable materials with improved mechanical properties.

1) Introduction 2) Directional solidification and related defects 2.1) Generalities on the casting processes 2.1.1) The Bridgman-Stockbarger casting process 2.1.2) Alternate casting processes 2.2) Casting defects 2.2.1) Crystal structure 2.2.2) Microstructure and microsegregation 2.2.3) Freckles 2.2.4) Deformation related defects 3) Heat treatments and microstructure optimizations 3.1) Generalities on heat treatments 3.1.1) Solution heat treatment 3.1.2) Aging heat treatments 3.2) Defects and optimizations 3.2.1) Incipient melting 3.2.2) Optimizations 4) Mechanical properties sensitivity to the processing parameters 4.1) Creep and tensile properties 4.2) Fatigue properties 5) Conclusions References

of changes in the material properties reflected by parameters such as the strain energy density of the hardness can be detected by uniaxial tests. The increase in the hardness of the 2024-T42 AI alloy caused by fatigue is examined. The amount of increase would depend on the material properties, the stress amplitude and the number of the cyclic loading. A non-linear relation is proposed between the hardness and the number of the cyclic loading such that the degree of non-linearity depends on an exponent that is a function of the fatigue stress amplitude. Numerical results are discussed in connection with previous work and presented graphically. Graphs. The effect of intermittent heating on fatigue crack growth. Lain, Y.C. and Griffiths, J.R.

of changes in the material properties reflected by parameters such as the strain energy density of the hardness can be detected by uniaxial tests. The increase in the hardness of the 2024-T42 AI alloy caused by fatigue is examined. The amount of increase would depend on the material properties, the stress amplitude and the number of the cyclic loading. A non-linear relation is proposed between the hardness and the number of the cyclic loading such that the degree of non-linearity depends on an exponent that is a function of the fatigue stress amplitude. Numerical results are discussed in connection with previous work and presented graphically. Graphs. The effect of intermittent heating on fatigue crack growth. Lain, Y.C. and Griffiths, J.R.

effect of Nb and C additions on the phase composition, microstructure, and creep resistance of Fe 3 Al-type alloys is investigated. Two alloys, which contained (at. pct) (i) 27.6 Al, 1.15 Nb and 0.19 C (Fe balance) and (ii) 27.1 Al, 1.11 Nb, and 0.76 C (Fe balance), were studied in a temperature range from 873 K to 1073 K (600 °C to 800 °C). The carbide in both alloys was identified as Nb 6 C 5 . The creep data can be rationalized by introducing a threshold stress, below which, the creep rate is negligible. The threshold stress and an effective stress exponent were found simultaneously by a numerical method. Using the obtained values of the threshold stress, the activation energy of creep was determined to be 328 kJ/mol. The effective stress exponent varied from 2.0 to 3.1. A breakdown of power-law behavior was observed at higher stresses. The transition occurred at the normalized creep rate of _ e=D ¼ 10 13 m À2 , which agrees with the rule suggested by Sherby and Burke and the diffusion coefficient D corresponding to the diffusion of Al in Fe-Al.

A crept modified 2(1/4)Cr-Mo steel (T24) was investigated in order to understand differences in creep behavior which are related to different cooling rates after austenitizing (air-cooling and water quenching). Two 823 K creep stress levels were compared, 150 MPa (rupture times of the order of: 50,000 h) and 200 MPa (rupture times of the order of: 500 h). The air cooled specimens showed lower rupture times at 200 MPa (short term creep conditions) while the differences in rupture times were not pronounced at 150 MPa (long term creep tests). The minimum creep rates were always faster for the air cooled material state. Microscopic techniques, documenting length scales from the mm (optical microscopy) to the nm range (transmission electron microscopy) were used to study microstructures. Water quenching results in the formation of martensite while air cooling produces bainitic microstructures. After creep, the water cooled specimens still show a finer microstructure (tempered martensite which is equivalent to a fine bainitic structure) than the air cooled specimens (coarse bainite). This mesoscopic microstructural difference can be documented using optical microscopy and scanning electron microscopy, and accounts for the differences in minimum creep rates and rupture times. No significant differences were found when using transmission electron microscopy (TEM) to study the two microstructures (fine and coarse bainite) after creep. M 23 C 6 (on internal interfaces), MX precipitates (on internal interfaces and in the matrix) and M 6 C carbides were detected in both microstructures. TEM observations suggest that interactions between small and stable MX precipitates and dislocations provide the high creep strength. Long term creep conditions result in the formation of molybdenum-rich M 6 C carbides which were not observed after short term creep exposure. These M 6 C carbides form close to M 23 C 6 particles. Moreover, it was found that the Mo-content of the MX precipitates increases during long term creep.

The creep behaviour of the intermetallic Fe-28Al-3Cr alloy with Ce additive was investigated at temperatures from 500 to 900 • C. The effect of the thermal processing was studied. The properties (e.g. time to rupture, minimum creep rate (MCR), the ultimate deformation) were improved by introducing small particles originating in the temperature interval from 600 to 800 • C.

The evolution of dislocation density in two tempered martensite ferritic steels (a 12% and a 9% chromium steel, "X20" and "P91") during heat treatment and creep is analyzed using transmission electron microscopy (TEM) and Xray diffraction (XRD); both methods yield results which are in good agreement when rationalizing the XRD-data based on densities of free dislocations. It is shown that due to the intermediate formation of martensite, standard heat treatments produce very high dislocation densities in tempered martensite ferritic steels (TMFSs). Long term tempering and creep are characterized by a decrease of dislocation density; but dislocation densities are still high as compared to alloys where the formation of microstructure does not involve a martensitic transformation. A heterogeneous microstructure after long term tempering and creep is a characteristic feature of TMFSs. Micro grains with high dislocation densities co-exist next to micro grains without dislocations. The XRD method yields average data and cannot account for this microstructural heterogeneity; but it supports the TEM results which in isolation suffer from providing insufficient statistics. The results of the present study are discussed in the light of earlier work published in the literature and contribute to a better understanding of the role of free dislocations in TMFSs during tempering, creep and high temperature low cycle fatigue.

The mechanical properties of polymeric materials change over time, especially when they are subjected to long term loading regimes. The short- and long-term creep behaviours for an amorphous polymer, poly(methylmethacrylate), have been investigated. A new creep compliance equation has been developed and validated, yielding a fully coupled time-temperature formulation, with long-term predictive capability. Based on short-term creep data, the long term creep behaviour of PMMA at 40oC was predicted using a model which is based on physical mechanisms responsible for the material’s behaviour.

Non-linear creep is described by a non-simulative, analytical, dynamic molecular modelling approach. Elementary, molecular-scale, process-relevant frequencies are derived by adequate kinetic formulation. They follow almost exactly an Arrhenius-like behaviour with a range of activation enthalpies. Their relative contribution to the overall macroscopic behaviour of the materials is quantified to account for the materials’ retardation time spectra and final non-Arrhenius behaviour. A new creep compliance equation is derived, yielding a fully coupled timetemperature- stress formulation, with long-term predictive capability. Experimental data for poly(methyl methacrylate) are analysed to identify the extent to which timetemperature and time-stress correspondence relationships may be valid, and it is shown that they are approximations (especially the latter), limited to narrow ranges of experimental variables, in contrast to the proposed model, which more reasonably fits the experimental ...

ABSTRACTWe have previously devised a simple method for quantifying the creep resistance of silk fibres – i.e. the ability of silk to maintain dimensional stability while supporting a constant load. We demonstrated (C. Smith et al., J. Arachnol. 31:421–424, 2003) that creep of spider dragline is significant at stresses that are small compared to the conventional yield strength. In addition, the existence of a limiting creep stress was revealed: if samples are loaded smoothly and quickly to a constant stress lying above the limiting creep stress, they break within a few seconds of the stress being applied. The magnitude of the limiting creep stress is equal to approximately one fifth of the fracture stress recorded in conventional constant strain rate tests (in which the stress is applied more gradually).Here we develop the method and broaden the study of creep to investigate the effects of immersion in water and in ethanol. Experiments are conducted by attaching a small weight (an ap...

Nature offers useful lessons on how fibres with controlled properties can be produced from sustainable starting materials under environmentally friendly conditions. As we begin to learn these lessons, the advantages that they offer have to be weighed against Nature's limitations: the same molecular features that make biomolecular fibres initially processable in water are also reflected in the fibres having water-sensitive properties, which may not be attractive in an engineering material. Particular attention is given to recent findings that the short-term impressive tensile properties of spider dragline silk as recorded in conventional tests performed at constant strain rate are compromised by creep and stress relaxation, especially in humid environments. Some practical steps towards applying Nature's lessons while addressing the constraints of these lessons are suggested.

This research explores industrial waste materials (waste plastic bottle and waste sachet water) as potentially modifiers for Hot Bitumen Mix (HBM) and Warm Bitumen Mix (WBM). This research becomes necessary because of the poor performance of HBM and WBM. Review of literature revealed that independent use of Waste Plastic Bottle (WPB) and Waste Sachet Water (WSW) significantly enhanced the performance of HBM and WBM. However, literature is scanty on blended use of WPB and WSW. The HBM samples were produced using 60/70 penetration grade of bitumen. Additive (sasobit) was added to the bitumen at 3.5 wt. % of the bitumen for the production of WBM. The HBM and WBM were modified by incorporating blended WPB and WSW thereby forming a composite mixture. The composite was varied at a proportion of 0-18 wt. % at 2% interval by 1:1 of the bitumen. The index properties of the HBM and WBM were analyzed. The modified HBM and WBM samples were characterized for microstructure using the X-Ray Fluorescence (XRF). The softening point and penetration index increased with increasing composite mixtures. The penetration reduced with increasing content of the composites. However, the optimum performances were obtained at 10 and 14 wt. % of WPB and WSW for HBM and WBM replacement, respectively, with specific gravity, penetration index, ductility and viscosity of 96, 54, 92, and 75% for HBM and 91, 32, 88, and 89% for WBM, higher than the control mix, respectively. The XRF revealed an enhancement in the adhesion and interlocking in the mineral structure. Exploring WPB and WSW as a modifier for the bitumen mixtures is feasible due to the improved performance of the bitumen mixes. Furthermore, incorporation of the waste materials through their conversion into useful raw materials is an environmental way of waste disposal, and sustainability.

This paper presents a finite element analysis of the small punch creep test for 316L(N), which is compared with experimental data for 650 and 700 °C. Special emphasis is placed on (i) assessing the influence of friction and (ii) comparing two different creep models: the simple Norton creep and the more general creep model. The computed normalized deflection rate versus time is almost identical for all cases, which allows for scaling of the results. The computed time to rupture increases linearly with the friction coefficient due to a reduction in the mean stress. There is a good overall agreement between the experimental values and the computed deflection rate for a friction coefficient of around 0.3. It is shown that the initial reduction in deflection rate is due to stress relaxation and homogenization, and is only marginally affected by primary creep hardening. The computed results are compared with the equivalent stress and strain rates in the recently published small punch stan...

A model that describes creep behavior is essential in the design or life assessment of components and systems that operate at high temperatures. Using the RCC-MRx data and the LCSP (logistic creep strain prediction) model, processed design data were generated over the whole creep regime of 316L(N) steel—i.e., primary, secondary, and tertiary creep. The processed design data were used to develop three models with different approaches for the creep rate: a phenomenological approach; an artificial neural network; and an artificial intelligence method based on symbolic regression and genetic programming. It was shown that all three models are capable of describing the true creep rate as a function of true creep strain and true stress over a wide range of engineering stresses and temperatures without the need of additional micro-structural information. Furthermore, the results of finite element simulations reproduce the trends of experimental data from the literature.

This study aims to investigate the impact of control and warm mix binders modified with nano-silica on the asphalt binder functioning to resist rutting endurance and low-temperature cracking. The percentages of nano-silica employed in this research were 2%, 4%, and 6% of asphalt binder weight. The control and modified binders were evaluated by performing conventional and rheological tests. The rheological properties were examined by master curves, isochronal plots, multiple stress creep recovery (MSCR), Superpave rutting parameter, and bending beam rheometer. The outcomes implied that the performance of the asphalt binder (with or without ZycoTherm) improved when nano-silica was added concerning (G*/sin δ) parameter. The MSCR test demonstrated that the recovery (R %) of the control and warm mix binders improved whereas the non-recoverable creep compliance (Jnr) dropped, implying that nano-silica boosted the rutting potential. Moreover, it was observed at different temperatures that ...

The impact of base and zycotherm binders modified with various proportions of nanosilica (i.e., 2 %, 4 %, and 6 %) based on the weight of the binder at high-temperature performance was investigated. Brookfield viscosity, penetration, softening point, and storage stability tests were all conducted on base and modified binders. Moreover, the Superpave rutting parameter (G*/sin δ) and Multiple stress creep recovery (MSCR) were utilized to assess the resistance of binders to rutting. By observing the outcomes of the modified binder tests, the incorporation of nanosilica into the base and zycotherm binders improved temperature susceptibility. Binders modified with nanosilica showed remarkable storage stability at elevated temperatures, as the variation in softening point between the upper and bottom parts was less than 2.5 °C for all binders. Based on the outcomes of the Superpave rutting parameter, the inclusion of nanosilica enhanced the stiffness of the modified binders up to 130 % fo...

The creep behavior and microstructures of extruded Mg 97 Zn 1 Gd 2 alloys with long period stacking ordered (LPSO) phase have been investigated. Creep properties of extruded alloys depend on pre-extrusion aging temperature; the optimum aging temperature to obtain excellent creep resistance is between 623 and 723 K. In this temperature range, a multimodal microstructure develops during subsequent extrusion at 623 K. The ¡-Mg matrix are bimodally grained; that is, it consists of fine DRXed grains and h10 10i//ED fiber-textured coarse grains. The LPSO phase grains also develop the h10 10i//ED fiber texture. Coarse block-shaped LPSO phase promotes dynamic recrystallization in ¡-Mg matrix via particle stimulated nucleation, while both fine plate-shaped LPSO phase and solute-segregated stacking faults (SFs) stimulate h10 10i//ED fiber texture evolution in the ¡-Mg matrix. The creep strength increases with increasing area fraction of the h10 10i//ED fiber textured region (coarse ¡-Mg grains and LPSO phase grains). Formation of plate-shaped LPSO phase and/or solute-segregated SFs before extrusion is most desirable for enhancing the creep properties of extruded Mg 97 Zn 1 Gd 2 alloys, due to LPSO phase-stimulated texture evolution.

Currently, additive manufacturing (AM) experiences significant attention in nearly all industrial sectors. AM is already well established in fields such as medicine or spare part production. Nevertheless, processing of high-performance nickel-based superalloys and especially single crystalline alloys such as CMSX-4 Ò is challenging due to the difficulty of intense crack formation. Selective electron beam melting (SEBM) takes place at high process temperatures (~1000 °C) and under vacuum conditions. Current work has demonstrated processing of CMSX-4 Ò without crack formation. In addition, by using appropriate AM scan strategies, even single crystals (SX SEBM CMSX-4 Ò ) develop directly from the powder bed. In this contribution, we investigate the mechanical properties of SX SEBM CMSX-4 Ò prepared by SEBM in the as-built condition and after heat treatment. The focus is on hardness, strength, low cycle fatigue, and creep properties. These properties are compared with conventional cast and heat-treated material.

A suggested method to describe the creep behaviour of paperboard in edgewise compression works for paperboard in the same way as for other polymers . The relation between stress, strain and time may be determined by a simple equation involving two factors, a power function of time and a factor describing the non-linear behaviour of the stress-strain curve. For engineering purposes, it is an advantage to be able to design a given product in terms of stress and strain in isochronous curves . In some applications the critical design criteria may be governed by a critical strain . For such applications isometric curves, i.e. stress versus time at different strains, are used. The strain at break in compression of the investigated paperboards was found to be independent of time. The strain to break in creep was equal to the strain at break for stress-strain testing under straincontrol. By inserting the strain at break in creep in the creep equation, the isometric curve at break could be derived which by definition gives the relation between stress and lifetime. The data in this investigation indicate that a rather small number of specimens and a reasonably short creep time are sufficient to provide a

Hardness of materials depend on the applied load and on the shape of the indenter. Various models regarding the indentation size effect have been developed to evaluate this load-dependence which necessitates numerous indentation tests to be valid. The aim of this paper is to reduce substantially the number of tests by calculating the universal hardness on the entire loading curve of a load-depth registration. The use of universal hardness instead of Oliver and Pharr method is required by the comparison with the conventional Vickers hardness. The protocol can be well supported if some improvements in depth-sensing indentation are made like the consideration of the frame compliance of the instrument, the creep displacement calculated as a function of the load and the rounded tip into the indentation depth measurement and consequently into the universal hardness calculation. Additionally, we show that the indentation size effect may be well-represented by the strain gradient plasticity theory whereas significant deviation is observed when only partial depthcorrections are made.

L’étude du comportement en fluage et en relaxation de matériaux soumis à des conditions sévères en termes de température, de contrainte et de déformation est nécessaire mais parfois coûteuse avec les essais classiques. En effet, ces essais, particulièrement celui du fluage, sont très consommateurs de temps, ils peuvent durer plus d’une année. Pour ramener cette durée d’essais à quelques minutes, nous proposons d’utiliser l’indentation instrumentée qui, avec l’évolution des conditions d’application de la charge et du déplacement de l’indenteur, permet de solliciter le matériau dans des conditions de chargement proches de celles imposées dans les essais classiques. Dans cette étude, nous proposons d’étudier le comportement de deux aciers au chrome utilisés pour la fabrication d’appareils sous pression. Il s’agit des aciers à 9 % de chrome (T91) et à 2,5 % de chrome (T22), l’objectif étant de classer les matériaux selon leur sensibilité au fluage et à la relaxation. Dans ce travail, no...

Hardness of materials depend on the applied load and on the shape of the indenter. Various models regarding the indentation size effect have been developed to evaluate this load-dependence which necessitates numerous indentation tests to be valid. The aim of this paper is to reduce substantially the number of tests by calculating the universal hardness on the entire loading curve of a load-depth registration. The use of universal hardness instead of Oliver and Pharr method is required by the comparison with the conventional Vickers hardness. The protocol can be well supported if some improvements in depth-sensing indentation are made like the consideration of the frame compliance of the instrument, the creep displacement calculated as a function of the load and the rounded tip into the indentation depth measurement and consequently into the universal hardness calculation. Additionally, we show that the indentation size effect may be well-represented by the strain gradient plasticity theory whereas significant deviation is observed when only partial depthcorrections are made.

This study is conducted to enhance the performance of bitumen at high temperatures. To do so, styrene-butadiene-styrene (SBS) and Nanosilica polymer additives were used. Initially, pure bitumen versus bitumen 60/70 samples with 2.5%, 3.5%, 4.5%, and 5.5% SBS polymer, and modified bitumen samples with 4.5% SBS polymer and 1%, 2%, 3%, and 4% Nano-silica were prepared using a high shear mixer. Polymer separation tests, rolling thin film oven tests, dynamic shear rheometer tests, and rotational viscosity tests were performed on the modified bitumen samples. Preliminary results of the dynamic shear rheometer test showed that SBS polymer improved the high-temperature performance of bitumen and increased its resistance to permanent deformation. However, Nano-silica had a more significant effect than SBS in improving the high-temperature performance of bitumen. The combination of 4.5% SBS and 4% Nano-silica enhanced the hightemperature performance of bitumen. Additionally, the results of the bitumen separation test showed that combining bitumen with SBS polymer caused the polymer to separate from the bitumen. Nevertheless, adding 1% Nano-silica resolved this issue. Asphalt mixture samples for the above compounds were then prepared based on the Superpave mix design method, and a dynamic creep test was performed. The results of this test showed that the combination of SBS and Nano-silica polymers significantly increases the resistance of the mixture at high temperatures. The combination of 4.5% SBS polymer and 4% Nano-silica, compared to the control sample with pure bitumen at 50 °C and 60 °C, reduces the cumulative strain by 51% and 41%, respectively, demonstrating the best

The intercritical annealing and isothermal bainitic processing response was studied for three Nb and V microalloyed Transformation-Induced Plasticity (TRIP)-assisted 980 MPa grade steels. Their mechanical and microstructural properties were compared to industrially produced TRIP 800 steel. Depending on the isothermal holding temperature and microalloying, the experimental steels reached properties comparable to the reference steel. The retained austenite content did not show direct correlation to elongation properties. Niobium was found to be more effective microalloying element than vanadium in increasing the elongation properties, which were investigated by measuring true fracture strain from tensile test specimens.

at Brownsville -Analysis of the GEO600 detector data has not shown any evidence of the existence of creep caused by hydroxide catalysis bonds in the mirror suspensions above the measurement sensitivity. Measuring directly the bond creep noise on samples of advanced detectors such as aLigo is a prudent research step. A system for direct detection of creep at a higher sensitivity is being design and mounted close to a set of aLIGO prototype test masses. Such system is based on capacitive sensors, which are used to measure any displacement either linear or rotational. This capacitive sensors are based on the electrical capacitance dependence of a conductor due to the distance from a dielectric body. A set of thermistors able to measure changes in temperature also form part of this setup. The goal is to be able to prove the presence of creep on the bonding used in the aLigo suspension test masses, and if such creep noise is presented find what produce it.

In this study, one of the most frequently used polymeric materials in fused deposition modeling (FDM) acrylonitrile butadiene styrene (ABS) is reinforced with different amount of carbon nanotubes (CNTs). Thermogravimetric analysis and differential scanning calorimetry analysis are applied to examine thermal degradation behavior of produced nanocomposite filaments. Specimens are manufactured by fused deposition modeling by using produced nanocomposite filaments. Tensile, creep and viscoelastic-viscoplastic behaviors of FDM-printed nanocomposite samples are investigated by conducting tensile, creep and loading-unloading tests under different strain rates and strain levels. Morphology of 3D printed samples is examined through scanning electron microscopy. Void densities which plays important role in mechanical behavior of additively manufactured samples are determined via ImageJ and CNT reinforcement on void densities are investigated. Data obtained from tests are used in system identification process, and multi-input-single-output model structures are proposed for the prediction of tensile, creep and recovery behaviors of 3D printed nanocomposite materials. Fused deposition modeling • Nanocomposite polymers • Creep behavior • Viscoelastic behavior • Identification • Artificial neural network 1 Introduction Fused deposition modeling (FDM), fused filament fabrication (FFF) or 3D printing has gained popularity over other B İlyas İstif

The south slope of the Vernago hydroelectric reservoir in northern Italy is subjected to a slow time-dependent movement that produced some structural damages in a service shaft located within it. With their continuation, these movements could also damage the diversion tunnel of the reservoir, leading to possible operational problems for the power plant. Two nonlinear, plane strain, finite element models of the slope were developed to evaluate the effectiveness of a berm to be constructed at the slope toe to reduce its present rate of deformation. They are based on different constitutive laws (namely: Viscoplastic and elastoplastic softening) the parameters of which were calibrated on the basis of the available geotechnical information and through the back analysis of inclinometer measurements. The critical evaluation of the results of the two numerical models singled out the inherent limits of one of them, in spite of the satisfactory outcome of the mentioned back analysis. The conclusion that can be reached from this example is that a successful back analysis does not necessarily guarantee a successful forward analysis.

The concrete liners of existing tunnels could present relevant damages due to their ageing or weathering, or to im- proper construction techniques. In some cases, depending on the geological conditions, these faults are due to the overstress caused e.g. by the occurrence of landslides, by swelling or creep of the rock mass, etc. Whilst two-dimensional numerical models are in most cases sufficient to assess the stress-strain state within the liner, a proper analysis of its replacement should be based on three- dimensional calculations. They, in fact, permit evaluating the need of soil/rock treatments around the tunnel and the length of the tunnel portions in which the liner demolition and re-construction can be safely carried out. In addition, they are necessary for a proper design of the new reinforced concrete support. Three level of tunnel rehabilitation are discussed, ranging from light repairs of the inner surface of the liner to heavy structural changes involving its demolition...

The south slope of the Vernago hydroelectric reservoir in northern Italy is subjected to a slow time-dependent movement that produced some structural damages in a service shaft located within it. With their continuation, these movements could also damage the diversion tunnel of the reservoir, leading to possible operational problems for the power plant. Two nonlinear, plane strain, finite element models of the slope were developed to evaluate the effectiveness of a berm to be constructed at the slope toe to reduce its present rate of deformation. They are based on different constitutive laws (namely: Viscoplastic and elastoplastic softening) the parameters of which were calibrated on the basis of the available geotechnical information and through the back analysis of inclinometer measurements. The critical evaluation of the results of the two numerical models singled out the inherent limits of one of them, in spite of the satisfactory outcome of the mentioned back analysis. The conclusion that can be reached from this example is that a successful back analysis does not necessarily guarantee a successful forward analysis.

The dissimilar GTAW weld joints between P22 (2.25Cr-1Mo) steel and P91 (9Cr-1Mo)
steel have become a common practice in power plants. However, an issue arises after
welding, as the heat affected zone (HAZ) of these dissimilar weld joints often exhibits
high hardness values. This elevated hardness in the HAZ is attributed to the
transformation of austenite to martensite due to the rapid cooling rate during the welding
process. Unfortunately, improper post weld heat treatment (PWHT) can exacerbate the
situation, leading to a significant disparity in hardness between the P91 steel and the weld
metal. Such a discrepancy in hardness can potentially give rise to cracks and failures
during high-temperature operations. Therefore, it is imperative to establish appropriate
post weld heat treatment protocols and cooling conditions in order to minimize the
disparity in hardness.
The research outlined in this book delves into the microstructure and mechanical
properties of weldments comprising 2.25Cr-1Mo steel (P22) and 9Cr-1Mo steel (P91),
both before and after the application of preheating and/or post weld heat treatment. The
weld zone and heat affected zone in P22 and P91 were subjected to mechanical testing
and metallurgical examination prior to and following welding and PWHT. Specifically,
the PWHT investigation was carried out on the weldments. After the welding process, the
samples were heated to a simulated service temperature of 750 °C, with varying holding
times of 8, 15, 30, 45, 60, 90, 105, 120, 135, and 150 minutes, respectively. These
samples were subsequently compared in terms of their microstructure and hardness.
This book sheds light on the profound impact of TIG welding on the formation of
the weld pool and the HAZ of P91 and P22 steels, supported by statistical analysis
utilizing the one-way ANOVA technique with a 95% confidence level. Furthermore,
metallurgical images of the weld pool and HAZ are presented to validate the findings. It
is important to emphasize that this study is experimental in nature, aiming to bridge the
knowledge gap in the field of dissimilar weld joints, GTAW weld joints, heat affected
zones, weld pools, hardness and the application of one-way ANOVA as a statistical tool.
The insights gained from this research will contribute to the development of improved
welding practices and post weld heat treatment methodologies.

The workshop, sponsored by the U.S. Department of Energy (DOE) and Office of Energy Research (ER), met its primary objective -to promote discussion among evaluation experts and DOE research managers on developing approaches for assessing the impact of DOE basic research upon the DOE energy mission, applied research, technology transfer, the economy and society.

In this study, depth-sensing indentation creep response of cast and additively manufactured (laser powder bed fusion) NiTi alloys in heat-treated conditions have been investigated at ambient temperature. Indentation creep tests were evaluated with the help of a dual-stage approach comprising a loading segment with a subsequent constant load-holding stage and an unloading phase afterward. The investigation was carried out at a maximum load of 50 mN along with a holding time of 600 s. Different creep parameters comprising indentation creep displacement, creep strain rate, creep stress exponent as well as the indentation size effect have been analyzed quantitatively for the employed materials. In addition, microstructural analysis has been performed to ascertain the processing–microstructure–creep property correlations. A substantial indentation size effect was seen for both cast and printed NiTi samples in heat-treated conditions. According to the creep stress exponent measurements, t...