Papers by Patricia Frontini
Mechanics of Materials, 2022
Polymer Engineering and Science, 2018
Weld lines occur when two melt streams are combined. They may result in purely cosmetic imperfect... more Weld lines occur when two melt streams are combined. They may result in purely cosmetic imperfections, but also may represent part failure if placed in an area on the plastic highly subjected to stress during service. Qualitative assessment of these structural and cosmetics defects is usually accomplished by conventional mechanical characterization, destructive by nature, such as tensile testing or dynamic mechanical analysis (DMA). Nanoindentation offers the possibility for quick quasi-nondestructive in situ testing, allowing for monitoring the changes that occur in the surface layer of a plastic micropart. In this study, a methodology for the assessment of the superficial properties: hardness (H) and reduced Young's modulus (E r) of micromolded parts was developed. The microparts, molded from Polyoxymethylene with two different sets of processing conditions were tested throughout the entire length and in the vicinity of the welding line. The observed hardness (H) and reduced Young's modulus (E r) suggest that there is a steady increase in both values along the weld line from the adjoining flow front point at the inner side of the micropart towards the outer edge. In addition, H and E r were found out to vary consistently with the alterations induced by the processing conditions. POLYM.
Journal of Reinforced Plastics and Composites, 2019
In this work, the residual strength of a fiber-reinforced injection molded part containing a hot ... more In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Injected plates were generated using a double-gated mold under four different process conditions. Quantification of the weld line detrimental effect was made in base on a fracture mechanics experiment. Specimens with and without the weld line—obtained from the same plates—were tested under a clamped single edge notched tension (SENT) configuration. For each set of process conditions, a relative weld line strength factor was defined in terms of the maximum applied stress intensity factor (KImax) as: KImax of specimens with weld line/KImax of specimens without weld line. In parallel, the fiber distribution pattern was obtained by process simulation software Moldex3D. An orientation factor was determined from simulation in order to quantify the effect of the local fiber orientation around the weld line. Optimal process condition and the most significant...
Waste and Biomass Valorization, 2017
Acta Scientiae et Technicae, 2015
No presente trabalho, a morfologia e as propriedades mecânicas de misturas PP/amido termoplástico... more No presente trabalho, a morfologia e as propriedades mecânicas de misturas PP/amido termoplástico (TPS) foram avaliadas. As misturas foram processadas em extrusora dupla rosca co-rotacional. O teor de amido presente nas misturas foi de 10, 20 e 30% (m/m). A resistência à tração do PP mostrou uma queda muito pequena com a adição do TPS, enquanto o módulo elástico não sofreu variação. O alongamento na ruptura decaiu com o aumento do teor de amido, devido à pobre interação interfacial entre a matriz hidrofóbica e a fase dispersa hidrofílica. A incorporação de amido na matriz de PP conduziu a um aumento significativo na resistência ao impacto do material final. A microscopia eletrônica de varredura confirmou a falta de interação interfacial entre as fases presentes na mistura.
Revista De Plasticos Modernos Ciencia Y Tecnologia De Polimeros, 2000
Journal of the Mechanical Behavior of Biomedical Materials, 2016
To these days, the production of a small diameter vascular graft (o6 mm) with an appropriate and ... more To these days, the production of a small diameter vascular graft (o6 mm) with an appropriate and permanent response is still challenging. The mismatch in the grafts mechanical properties is one of the principal causes of failure, therefore their complete mechanical characterization is fundamental. In this work the mechanical response of electrospun bilayered small-diameter vascular grafts made of two different bioresorbable synthetic polymers, segmented poly(ester urethane) and poly(L-lactic acid), that mimic the biomechanical characteristics of elastin and collagen is investigated. A J-shaped response when subjected to internal pressure was observed as a cause of the nanofibrous layered structure, and the materials used. Compliance values were in the order of natural coronary arteries and very close to the bypass gold standard-saphenous vein. The suture retention strength and burst pressure values were also in the range of natural vessels. Therefore, the bilayered vascular grafts presented here are very promising for future application as smalldiameter vessel replacements.
BioResources, 2015
Reducing the consumption of phenol during synthesis of phenolic resins is of great technological ... more Reducing the consumption of phenol during synthesis of phenolic resins is of great technological and scientific interest because of its economic and environmental implications. In this work, the use of hydroxymethylated lignins as a partial replacement for phenol in resol phenol-formaldehyde resins used for the production of decorative laminates was experimentally studied. The work involved: i) the industrial synthesis of traditional and modified resols with 10%w/w of sodium lignosulfonate and kraft-type lignin; ii) the industrial impregnation of krafttype paper with the produced resins; iii) the production of laminates on both laboratory and industrial scales; and iv) the measurement of their final properties. The mechanical performance of the laminates was evaluated via the determination of the Young modulus, bending strength, biaxial impact strength, and Mode-I interlaminar fracture toughness. The (modified and traditional) laminates exhibited statistically significant differences in mechanical properties. However, the partial lignin replacement did not produce effects that were detrimental to the overall performance of the decorative laminates.
Polymer Testing, 2015
Round robin tests carried out under the direction of the Technical Committee 4 of the European St... more Round robin tests carried out under the direction of the Technical Committee 4 of the European Structural Integrity Society (ESIS TC4) have shown that, for determining the fracture resistance of ductile polymers at low loading rates, the multi-specimen methodology based on the construction of the material crack growth resistance curve often does not provide reliable data due to the uncertainties associated with the measurement of crack advancement (Da). With the aim of strengthening this multi-specimen methodology, the ESIS TC4 attention has been recently focused on the analysis of a testing scheme based on the load separation criterion, which does not require the measurement of Da. The present work gives the results of a multi-laboratory round-robin testing exercise carried out by ESIS TC4 in order to assess the degree of reproducibility of the fracture parameters obtainable with the application of this load separation criterion based testing scheme. Encouraging results have been obtained.
Procedia Materials Science, 2015
Mechanical characterization of hydrogels is a challenging task because they are much softer than ... more Mechanical characterization of hydrogels is a challenging task because they are much softer than metals, ceramics or polymers. The elastic modulus of hydrogels is within 10 0-10 2 kPa range. Because they easily break and slump under their own weight, tensile and bending tests are not suitable configurations to assess elastic modulus. This work reports on the determination of elastic modulus of a gelatin gel by indentation experiments. Indentation is very simple configuration, it is of technological importance and it can be applied at different length scales with high accuracy. The gelatin hydrogel behavior is first calibrated by uniaxial compression and low strain rheological measurements. It behaves as a hyperelastic solid with strain hardening capability at large strains and shows no dependence with frequency in the linear viscoelastic range. It can be properly characterized by the First order Ogden material model. Indentation experiments are carried out at macro and nanoscales using spherical and flat-ended cylindrical punches. Elastic contact solutions and inverse analysis accounting for hyperelasticity are used to extract the elastic modulus from experimental force-depth curves. Adhesion between punch and hydrogel influences the indentation response and affects the accuracy of elastic modulus determination in a larger extent than the assumption of linear elasticity. Adhesion leads to overestimation of elastic modulus values. The influence of adhesive forces increases with decreasing the length scale. A markedly decay of elastic modulus with increasing maximum load is observed at nanoscale. A hybrid model based on Hertz elastic contact solution and Johnson-Kendal-Roberts model for adhesion is used to determine elastic modulus. This model yields an elastic modulus in good agreement with that obtained from uniaxial compression test.
Industrial & Engineering Chemistry Process Design and Development, 1983
To = feed temperature, O C TR = reactor bed temperature, O C T, = wall temperature, O C To, = ave... more To = feed temperature, O C TR = reactor bed temperature, O C T, = wall temperature, O C To, = average temperature of oil in cooling coils, O C ub = bubble rise velocity, cm/s ud = superficial velocity at minimum fluidization, cm/s uH2 = feed rate of hydrogen at STP, cm3/min UC, = feed rate of butane at STP, cm3/min u, = superficial gas velocity, cm/s V = total volume of the bed, cm3 V , = average bubble volume, cm3 V , = volume of emulsion phase, cm3 uo = total volumetric flow rate of inlet gas, cm3/s W = weight of catalyst, g z = 2-transform variable 2 = time history vector for the three temperatures, TR, T,, 2 = the estimate of 2 from the model Greek Letters z = bed void fraction, dimensionless tS3, = propane selectivity error at time t zTRI-= temperature error at time t pgaverage molal density of gas, g-mol/cm3 pp = average particle density, g/cm3 T = process time constant 0 = process dead time X = desired closed loop time constant (a tuning parameter in Dahlin's algorithm) 6 = desired closed loop dead time 9 = proportionality constant in eq 8 Toil
International Journal of Impact Engineering, 2016
It is introduced in this paper a Lattice Discrete Element Method (LDEM) for modelling the falling... more It is introduced in this paper a Lattice Discrete Element Method (LDEM) for modelling the fallingweight test of polymethyl-methacrylate (PMMA) specimens. The method exploits the inherent characteristics of discrete methods to model crack initiation and propagation by simply breaking the links between their discrete components. It results in a flexible modelling tool that is implemented using Abaqus/Explicit. Numerical results are validated by comparison with experimental tests. The results are compared in terms of the time evolution of the striker force and velocity and the specimen crack patterns. The LDEM simulations are, in every case, of predictive nature. Material properties are neither left open for calibration nor used to adjust the numerical results. There is a good agreement between experimental and numerical results. It is shown that the proposed LDEM has the capability to capture all the main features of the sequence of events that occur during the experiment: the elastic specimen loading prior to the crack initiation, the nucleation and propagation of radial cracks as the test progresses, and the final failure after the rapid propagation of a circular crack that joins the radial cracks together. The effects of the variability of the material fracture toughness on the test results are studied using a series of models with random distribution of the fracture energy.
Experimental Mechanics, 2015
This paper explores the feasibility of characterizing the mechanical response of the commercial a... more This paper explores the feasibility of characterizing the mechanical response of the commercial aerospace grade epoxy resin RTM6 by nanoindentation tests at varying temperatures and strain rates. Since glassy polymers exhibit timedependent mechanical properties, a dynamic nanoindentation technique was used. This method consists on superimposing a small sinusoidal force oscillation on the applied force. Viscoelastic properties are then characterized by their storage and loss moduli, whereas the visco-plastic response of the material can be associated to its hardness. In such experiments, thermal stability of the measuring technique is critical to achieve a low thermal drift and it becomes increasingly important as the measuring temperature increases. Our results show that conventional methods applied for drift correction in nanoindentation of inorganic materials are not applicable to glassy polymers leading to physically inconsistent results. We propose a method for drift correction based on the hypothesis that viscoelastic modulus should be a function of the applied load and frequency but independent of the global strain rate. Using this method, it was possible to determine the viscoplastic properties of RTM6 between RT and 200°C.
Carbon-based coatings are known for their good mechanical and tribological properties. By tuning ... more Carbon-based coatings are known for their good mechanical and tribological properties. By tuning the C sp3-to-sp2 bonding ratio and by alloying the carbon with other elements, it is possible to tailor hardness, elasticity, friction and wear resistance. Also, polyether-ether-ketone (PEEK) polymers are increasingly used by the industry because of their corrosion resistance, mechanical stability, and self-lubricating ability. Huge amount of data regarding their individual interaction with steel counterfaces is available; however, very little information is found regarding the interaction of both materials. In this work, we studied mechanical and tribological properties of carbon nitride (CNx) and carbon fluoride (CFx) coatings sliding against PEEK. The coatings were deposited on SKF3-steel balls by high power impulse magnetron sputtering (HiPIMS) using an industrial deposition system CemeCon CC800/9ML. CNx was prepared at room temperature (RT) and 180 oC (HT) by reactive sputtering fro...
Polymer Gels and Networks, 1993
Elastic modulus (E) and yield stress in uniaxial compression (~v) were determined for a series of... more Elastic modulus (E) and yield stress in uniaxial compression (~v) were determined for a series of epoxy-amine networks prepared with different stoichiometric ratios. Tests were performed at room temperature, i.e. in the glassy state of the polymeric networks. Observed trends were analysed and compared with literature results. The following conclusions were obtained. (i) E depends both on packing density (p*) and sub-vitreous relaxations (To) that are active at the testing conditions, but (p*) is the predominant factor when it varies significantly in the particular series, i.e. Ap* ~ 10 2. (ii) The stress at the post-yield plateau (in uniaxial compression) may be correlated with the crosslink density of the epoxy network. (iii) There is no general relationship between E and ~rv as is frequently stated (Brown's rule).
Fracture and mechanical characterization of bone composite composed of polymethylmethacrylate and... more Fracture and mechanical characterization of bone composite composed of polymethylmethacrylate and hydroxyapatite (HA) at different contents was carried out. Hydroxyapatite is added in order to improve cement biocompatibility, but it is expected that it also affects mechanical properties. Specimens were either stored in air at 37 C for 120 h or in physiological solution (PhS-37), in order to establish the in¯uence of storage conditions upon mechanical behavior. One set of specimens was also postcured at 120 C for 4 h to take into account the in¯uence of free monomer. Fracture experiments revealed some nonlinearity in load±displacement records and differences in trends between initiation and propagation values of the fracture surface energies. The trends in the data shows that HA acts as a rigid ®ller enhancing fracture resistance,¯exural modules and yield stress, up to a certain content. Beyond the latter limit, properties suffer a deterioration because the addition of HA also affects the cement porosity. Absorbed water acts as plasticizer leading to a decrease in mechanical properties. The highest propagation strain energies were exhibited by materials aged in PhS-37.
eXPRESS Polymer Letters, 2009
eXPRESS Polymer Letters, 2007
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Papers by Patricia Frontini