Changes In Tensile Properties Research Articles

Evaluation of heat treatment regimes and their influences on the properties of powder‐printed high‐density polyethylene bone implant

AbstractA two‐step heat treatment was utilized as a means to improve the mechanical properties of a high‐density polyethylene structure which was fabricated using the three‐dimensional printing technique. It was found that the relationship between structure and properties was strongly influenced by heat treatment conditions including treatment times (15–60 min) and treatment temperatures (140–180 °C) of both primary and secondary steps. The use of primary heating at 180 °C for 15 min and secondary heating at 160 °C for 60 min resulted in the highest tensile modulus and strength, 0.7 GPa and 14.8 MPa, respectively. The changes in both shrinkage and tensile properties were governed by the level of residual porosity and quality of polyethylene interface in samples which were both influenced by the degree of thermally induced densification and binder degradation. Empirical correlations between porosity and shrinkage or tensile properties were found to be power functions. Copyright © 2010 Society of Chemical Industry

The microstructure and tensile property degradation of a gamma-TiAl alloy during isothermal and cyclic high temperature exposures

The microstructure and tensile property changes of a γTiAl-based alloy, Ti-47Al-2Cr-2Nb-0.15B, during isothermal and cyclic high temperature exposures have been investigated. Microstructure coarsening, including the fracture, dissolution and spheroidization of α 2 lamellae, is considered to be the main cause of the evident tensile property decreases of the alloy after isothermal and cyclic high temperature exposures. Dislocation emission near the broken lamellae is also an important phenomenon in the microstructure degradation during cyclic high temperature exposure, which originated from the thermal mismatch between α 2 and γ phases.

Effect of Welding and Post-weld Heat Treatment on Tensile Properties of Nimonic 263 at Room and Elevated Temperatures

Nimonic 263 has been developed for the improved ductility in welded assemblies and is a candidate material for gas turbine combustor and transition pieces along with its good weldability and mechanical properties at room and elevated temperatures. In this study, the tensile behavior of an as-welded Nimonic 263 specimen at room temperature and 1053 K (780 °C) was examined in conjunction with microstructural evolution during welding and postweld heat treatment (PWHT). With the welding and the PWHT, the yield strength (YS), ultimate tensile strength (UTS), and tensile elongation of Nimonic 263 varied in a complex manner. It was observed that the PWHT of resolutionization at 1423 K (1150 °C) for 2 hours gave the highest YS and UTS values, whereas the tensile elongation was the lowest, at both testing temperatures. With increasing resolutionization time, the YS and UTS tended to decrease along with the increase in tensile ductility. The tensile behaviors of as-welded Nimonic 263 specimens was affected by several factors, including grain size, residual stress, possible microsegregation of γ′ forming elements, a tendency for interdendritic or intergranular fracture and a morphological change in both M23C6 and MC type carbides, depending on the testing temperature and the PWHT. The complex changes in tensile properties of Nimonic 263 with welding and PWHT at room temperature and 1053 K (780 °C) were discussed based on the micrographic and fractographic observations.

Effects of chemical treatments of hybrid fillers on the physical and thermal properties of wood plastic composites

Hybrid filler reinforced composites are considered as a high performance materials, but limited numbers of researches on hybridizations of wood fibers and mineral fillers were reported. Generally, high amount of filler content in composites can lead to the reduction of interfacial adhesion between matrix polymer and fillers, and it limits their applications. In this study, we measured the changes of tensile strength, water absorption, and thermal properties of composites after chemical treatments to wood fibers and mineral fillers. Coupling agent had its own optimum amount for wood fibers and talc to obtain the highest tensile strength. Talc addition showed little effect of the tensile strength with alkali treated wood fibers. Talc addition and silane treatment showed opposite effects on water absorption. Melting enthalpy was decreased by addition of the fillers because of the reduced amount of the crystallizable resin and because of the interference of the fillers for crystallization process.

The influence of an aligned nanofibrous topography on human mesenchymal stem cell fibrochondrogenesis

Fibrocartilaginous tissues serve critical load-bearing functions in numerous joints throughout the body. As these structures are often injured, there exists great demand for engineered tissue for repair or replacement. This study assessed the ability of human marrow-derived mesenchymal stem cells (MSCs) to elaborate a mechanically functional, fibrocartilaginous matrix in a nanofibrous microenvironment. Nanofibrous scaffolds, composed of ultra-fine biodegradable polymer fibers, replicate the structural and mechanical anisotropy of native fibrous tissues and serve as a 3D micro-pattern for directing cell orientation and ordered matrix formation. MSCs were isolated from four osteoarthritic (OA) patients, along with meniscal fibrochondrocytes (FC) which have proven to be a potent cell source for engineering fibrocartilage. Cell-seeded nanofibrous scaffolds were cultured in a chemically-defined medium formulation and mechanical, biochemical, and histological features were evaluated over 9 weeks. Surprisingly, and contrary to previous studies with juvenile bovine cells, matrix assembly by adult human MSCs was dramatically hindered compared to donor-matched FCs cultured similarly. Unlike FCs, MSCs did not proliferate, resulting in sparsely colonized constructs. Increases in matrix content, and therefore changes in tensile properties, were modest in MSC-seeded constructs compared to FC counterparts, even when normalized to the lower cell number in these constructs. To rule out the influence of OA sourcing on MSC functional potential, constructs from healthy young donors were generated; these constructs matured no differently than those formed with OA MSCs. Importantly, there was no difference in matrix production of MSCs and FCs when cultured in pellet form, highlighting the sensitivity of human MSCs to their 3D microenvironment.

Effect of Workwear Fabric Characteristics on the Changes in Tensile Properties of Sewing Threads after Sewing

During sewing at high speed, the needle thread is subjected to repeated tensile stresses, heat, bending, pressure, torsion and wearing. These stresses act on the thread repeatedly and the thread passes 50–80 times through the fabric, the needle eye and the bobbin case mechanism, before getting incorporated into the seam. As a result both the sewing thread and the yarns in the fabric get abraded/ severed during the seaming process. A number of researchers observed that there could be 30% to 40% strength loss in the cotton needle thread after sewing. The extent of damage becomes more critical if the fabric being used is of a dense, thick and heavy construction. A number of studies have been carried out on thread strength loss after sewing, but the impact of fabric characteristics on thread strength loss is still unexplored. In this paper, the effect of weight and fabric composition of workwear fabrics, on the changes in the tenacity, breaking elongation and initial modulus of the needle thread has been studied. The tenacity and breaking elongation loss increase with increase in fabric weight for staple threads and remain unchanged for core spun threads. The loss in initial modulus increases for polyester threads as fabric weight increases, and decreases for cotton thread. When sewn on polyester-cotton fabric of same weight, the cotton thread shows decrease in tenacity and breaking elongation loss, whereas loss in initial modulus increases. The polyester core spun threads show exactly opposite change, i.e. tenacity and elongation loss increase and loss in initial modulus decreases when sewn on polyester-cotton fabric.

Effect of Pro-degradant Additives Concentration on Aging Properties of Polypropylene Films

This paper describes the effect of pro-degradant (PDA) additives on degradation behaviour of polypropylene (PP) films. Thin films (0.12 mm) containing this additives was prepared by sheeting process. The effect of natural exposure (NE) and heating of PP films in the presence or absence of additives were investigated. The apparent density value of PP film contained PDA are proportionate with PDA concentration. Meanwhile melt flow index (MFI) decreased as PDA concentration increased. Changes in tensile properties and carbonyl index (CI) were used to investigate the degradation behavior of the films. The results indicate that the presence of PDA contributes to the degradation and the activity is proportional to the amount of PDA. All samples were found to be more susceptible to thermo-oxidation than to natural exposure.

Investigation of the influence of different commercial softeners on the stability of poly(lactic acid) fabrics during storage

We have studied the potential degradation of poly(lactic acid)-based fabrics treated with commercial softeners and stored under two sets of conditions for one year. Initial wet-processing caused a fall in molecular weight of about 28%, irrespective of after-treatment. Storage at 40 °C and 80% RH produced further degradation which, with few exceptions, was aggravated by the presence of softeners. Ultimately, all samples degraded beyond the point of commercial usefulness. No clear distinction could be made between the effects of softeners having differing compositions. In contrast, fabrics stored under milder conditions of 23 °C and 50% RH showed no significant time-dependent polymer degradation, irrespective of the treatment applied. There were slight changes in tensile properties and some evidence of physical structural effects having occurred, which we attribute to physical aging. However, we do not believe these to be so serious as to call into question the long-term viability of PLA-based textile products.

Influence of the structures of polyamide 6 fibers on their ageing under intensive insolation conditions

The effects of large doses of UV radiation, relating to actual operational use during 1, 2 or 5 summer seasons, on changes of chemical structures, crystalline structures, morphology and tensile properties of four types of polyamide 6 were investigated. The fibers differed in cross-section shape and mat degree caused by TiO2 addition. The fibers were tested using, among others, SEM and IR methods. Critical dissolution time (CDT) was also investigated.

Effect of zinc oxide type on ageing properties of Styrene Butadiene Rubber compounds

The presence of zinc oxide in rubber compounds is tried to be minimized due to environmental concerns. In this study; the effect of different zinc oxide types on ageing properties of SBR compounds was investigated. Active zinc oxide and zinc oxide coat on CaCO 3 core were used in SBR compounds and their ageing characteristics were compared. The changes in tensile properties, hardness and rebound resilience were followed and evaluated.

Effect of Di(2‐ethyl hexyl phthalate)/Epoxidized Soybean Oil and Calcium Stearate/Zinc Stearate Ratios on the Tensile Properties of Plasticized PVC Formulations. A Study for Calcium Stearate Rich Formulations

AbstractTwo series of plasticized PVC formulations were prepared, containing one of the following di (2‐ethyl hexyl phthalate)/epoxidized soybean oil ratios (phr/phr): (a) 35/3, (b) 55/3, (c) 45/0 or, (d) 45/6. For each ratio, the following calcium stearate/zinc stearate ratios (phr/phr) were considered: (a) 0.6/0.4, (b) 0.8/0.2 or, (c) 1.0/0.0; all formulations were prepared with a total content of stearate(s) of 1.0 phr. The difference between the series was the preheating of stearates (150 °C, 90 min), carried out before the dry‐blend preparation. The changes of tensile properties produced by the degradation process were measured in ribbons obtained by extrusion.

Studies on the Changes in Tensile Properties of Sewing Thread at Different Sewing Stages

A lockstitch is formed by the interlacement of needle and bobbin threads. During high-speed sewing, needle thread is subjected to repeated tensile stresses, heat, bending, pressure, torsion, and wearing. Therefore, the mechanical properties of thread, which become altered during sewing, are very important for its performance and durability. In order to design a sewing machine and threads for maximum strength retention, it is important to understand how the mechanical properties of the thread change as it progresses through the machine and become incorporated into the seam. In this paper, the tensile properties of the needle thread are measured at four sewing stages: before sewing, after dynamic loading at the tension regulator, after passage through the needle and fabric, and after bobbin thread interaction. Mercerized cotton, polyester staple spun, polyester—cotton core spun, and polyester—polyester core spun threads are used and the contribution of dynamic loading, passage through the needle and fabric, and bobbin thread interaction to the change in tensile properties is analyzed. The loss in tenacity, elongation, and breaking energy for cotton thread is the highest, followed by polyester staple and core spun threads. However, the cotton thread shows lower loss in initial modulus as compared with the other threads. Bobbin thread interaction is mainly responsible for the loss in thread strength, elongation, initial modulus, and breaking energy for all threads, barring breaking elongation in cotton threads. Dynamic loading leads to an increase in the initial modulus for all threads. Passage through the needle and fabric assembly has a relatively small contribution to the reduction in tensile properties.

Effect of Process and Machine Parameters on Changes in Tensile Properties of Threads during High-speed Industrial Sewing

The dynamic, thermal, bending and abrasive loading of thread during sewing process has a negative influence on the properties of sewing threads. In this study, the individual and interactive effect of the number of fabric layers, stitch density and needle size on the loss in tenacity, breaking elongation and initial modulus of four types of thread has been studied using Box-Behnken design. Response surface regression equations of loss in tensile properties on the above parameters were developed. The predicted equations agreed well with the experimental data. Contrary to the general expectation, the loss in tenacity and breaking elongation was found to decrease initially or remain unchanged as the number of fabric layers increased. Initial modulus loss decreased with the increase in number of fabric layers for all threads. Except for cotton thread, stitch density did not show any significant influence on tenacity and breaking elongation loss. As the needle size increased, the loss in tenacity and breaking elongation increased for all polyester threads, whereas these properties remained unchanged for cotton thread. Analysis of variance was carried out to find out the contribution of parameters in loss in tensile properties. The number of fabric layers was found to have the highest contribution on tenacity and breaking elongation loss of cotton threads, whereas needle size contributed substantially to the loss in these properties of polyester threads.

Comparison of Embiopteran Silks Reveals Tensile and Structural Similarities across Taxa

Embioptera is a little studied order of widely distributed, but rarely seen, insects. Members of this group, also called embiids or webspinners, all heavily rely on silken tunnels in which they live and reproduce. However, embiids vary in their substrate preferences and these differences may result in divergent silk mechanical properties. Here, we present diameter measurements, tensile tests, and protein secondary structural analyses of silks spun by several embiid species. Despite their diverse habitats and phylogenetic relationships, these species have remarkably similar silk diameters and ultimate stress values. Yet, ultimate strain, Young's modulus, and toughness vary considerably. To better understand these tensile properties, Fourier transformed infrared spectroscopy was used to quantify secondary structural components. Compared to other arthropod silks, embiid silks are shown to have consistent secondary structures, suggesting that commonality of amino acid sequence motifs and small differences in structural composition can lead to significant changes in tensile properties.

Nb-Base FS-85 Alloy as a Candidate Structural Material for Space Reactor Applications: Effects of Thermal Aging

The proposed uses of fission reactors for manned or deep space missions have typically relied on the potential use of refractory metal alloys as structural materials. Throughout the history of these programs, a leading candidate has been Nb-1Zr, due to its good fabrication and welding characteristics. However, the less-than-optimal creep resistance of this alloy has encouraged interest in the more complex FS-85 (Nb-28Ta-10W-1Zr) alloy. Despite this interest, only a relatively small database exists for the properties of FS-85. Database gaps include the potential microstructural instabilities that can lead to mechanical property degradation. In this work, changes in the microstructure and mechanical properties of FS-85 were investigated following 1100 hours of thermal aging at 1098, 1248, and 1398 K. The changes in electrical resistivity, hardness, and tensile properties between the as-annealed and aged materials are compared. Evaluation of the microstructural changes was performed through optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The development of intragranular and grain-boundary precipitation of Zr-rich compounds as a function of aging temperature was followed. Brittle tensile behavior was measured in the material aged at 1248 K, while ductile behavior occurred in samples aged above and below this temperature. The effect of temperature on the under- and overaging of the grain-boundary particles is believed to have contributed to the mechanical property behavior of the aged materials.

Factors affecting the properties of PLA/CaSO4 composites: homogeneity and interactions

Composites were prepared from poly(lactic acid) (PLA) and a natural CaSO4 filler to study the developed struc- ture and the interaction of the components. The filler was characterized very thoroughly by several techniques and the results indicated that the filler contains a considerable amount of small particles with size much below the volume average size of 4.4 μm. The presence of these small particles did not result in inhomogeneity, considerable extent of aggregation was not observed in the composites. The filler was coated with stearic acid to modify interactions and optimum coverage corresponded to the amount estimated from the specific surface area of the filler. Mechanical properties changed only slightly with increasing amounts of the uncoated filler, but coating resulted in a drastic change of tensile properties and deformation behavior. Considerable plastic flow was observed around filler particles on the fracture surface of broken spec- imens. The quantitative estimation of interfacial interactions and their comparison to existing data proved that the interac- tion of PLA and CaSO4 corresponds to values observed in other mineral filled polymers. On the other hand, the reinforcing effect of the coated filler is extremely poor indicating almost zero interaction. Additional experiments proved that consid- erable amount of stearic acid dissolves in PLA and plasticizes the polymer. Stearic acid seems to desorb also from the sur- face of the filler, dissolve in the polymer and modify matrix properties.

Influence of heat treatment on microstructure and mechanical properties of Mg-10Gd-3Y-1.2Zn-0.4Zr alloy

Microstructure evolution and mechanical properties of the cast Mg-10Gd-3Y-1.2Zn-0.4Zr (mass fraction, %) alloy during annealing at 798 K for different time were investigated. In the as-cast state, the microstructure consists of α-Mg, Mg 5(Gd, Y, Zn) eutectic compounds and stacking faults(SF) of basal plane distributed from grain boundary to inner grain. During heat treatment at 798 K, the SF and parts of eutectic compounds dissolve into the matrix gradually, simultaneously, a new straight lamellar phase with 14H type of long period stacking ordered(LPSO) structure comes into being. Microstructure observation indicates that the lamellar phase is transformed from the un-dissolved eutectic compounds and shows a coarsening and disappearing process with annealing time prolonging. Three alloy specimens with typical microstructure after being annealed for 6, 36 and 72 h were selected to age at 498 K to peak hardness. Room and elevated temperature tensile tests show that the LPSO structured phase contributes to the change of high temperature tensile properties.

Changes in tensile properties for the PET films by the treatment in supercritical carbon dioxide fluid

Poly (ethylene terephthalate) films were treated in supercritical CO2 (s-CO2) fluid, and the modifications in tensile properties were investigated. The yield load peaks became ambiguous and the breaking strains and loads decreased for the treated films. However, the tensile modulus and the yield strain were almost unchanged after the treatments. The yield strain is related to the interplay between the amorphous entanglement density and the stability of crystal blocks. WAXD patterns for the films were hardly modified through the treatment. Thus the orientation for the crystal blocks seems to be unchanged. Moreover, laser Raman microprobe spectroscopic analyses revealed that the orientation of molecular chains is almost retained after the treatments. Thus it is natural to assume that the interplay between the amorphous entanglement density and the stability of crystal blocks will also be kept constant even though the swelling of amorphous regions with s-CO2 occurs during the treatments. From differential scanning calorimetry measurements, it was found that the heat of fusion for the crystallites was a little increased without shifting the peak position after the treatment. Therefore, the increase in crystallinity is not due to the thickening or crystal perfecting for primary lamellae, but due to the secondary crystallization. The increase in crystallinity caused by the secondary lamellae crystallized and combined onto the primary lamellae seems to have reduced the amorphous chains to be deformed easily at tensile tests. Then the breaking strains and loads decreased for the treated films.

Evaluation of activation energy for dynamic strain aging process in 316L(N)/316(N) SS weld joints

Type 316 L(N) Stainless Steel (SS) is being currently used as a structural material for various components of Prototype Fast Breeder Reactor (PFBR). The possibility of using 316 L(N) electrodes for fabrication of 316 L(N) welding joints is being critically examined. This paper discusses about the evaluation of activation energy for Dynamic Strain Aging (DSA) process in 316L(N)/316(N) SS Weld Joints. The Gas Tungsten Arc Welding (GTAW) process was used for the root pass and Gas Metal Arc Welding (GMAW) process was used for the remaining passes. Tensile tests have been conducted in the wide temperature range from room temperature to 1023 K at a strain rate of 3 × 10−3 s−1. Yield stress showed a continuous decrease with increasing temperature, with a plateau being observed between 823 and 923 K. A minima in elongation was also observed in this temperature range. These two properties being manifestations of dynamic strain aging, further tests at different strain rates (3 × 10−5 s−1 to 3 × 10−2 s−1) were conducted in this temperature range. Detailed analyses of the results were carried out and the solute responsible for dynamic strain aging was identified to be substitutional chromium. Post test analysis of fracture surfaces and deformation substructures were correlated with the changes in tensile properties at different testing temperatures.

A novel synthetic route for the preparation of hydrolytically degradable synthetic hydrogels

A variety of approaches have been described for the modification of synthetic, water soluble polymers with hydrolytically degradable bonds and terminal vinyl groups that can be crosslinked in situ by photo- or redox-initiated free radical polymerization. However, changes in macromer concentration, functionality, and molecular weight commonly used to achieve variable degradation rates simultaneously alter hydrogel mechanical properties. Herein, we describe a novel, two-step synthetic route for the preparation of hydrolytically degradable, crosslinkable PEG-based macromers based on chemical intermediaries that form ester linkages with variable alkyl chain length. Changes in the concentration of a single macromer were shown to provide effective variation of degradation, but with corresponding significant changes in tensile properties. Through variation in the alkyl chain length of the chemical intermediary, variable degradation times ranging from weeks to months are achieved, without significantly affecting initial gelation efficiency, swelling, or tensile properties. When modified with adhesive ligands, hydrogels supported viability of encapsulated and adherent cells. Controlled release of a model protein (Immunoglobulin G) was attained as a function of hydrogel degradation rate. Independent control of hydrogel degradation and mechanical properties will offer improved flexibility for studying the effect of these material characteristics on cellular function and may be useful in the design of matrices for tissue engineering and controlled release of bioactive molecules.