Ultimate Mechanical Properties Research Articles

Study of phase transition and ultimate mechanical properties of orthorhombic polyoxymethylene based on the refined crystal structure

The crystal structure of the orthorhombic polyoxymethylene (POM) has been refined by analyzing the synchrotron X-ray diffraction data measured for a micrometer-size single crystal of moth-type morphology. The 3-dimensional elastic and compliance constants tensors were calculated for both the trigonal and orthorhombic phases on the basis of the thus-obtained accurate structure information. The crystal structure information allowed us also to discuss the solid-state phase transition behavior from the orthorhombic to the trigonal phase occurring at around 78 °C. For this purpose, we have performed the temperature-dependent synchrotron X-ray scattering measurement for a tiny moth-type single crystal and revealed the geometrical relation between these two crystals. The free energy was calculated as a function of temperature for these two accurately-analyzed crystal forms using a density functional theory (DFT). The result showed that the orthorhombic phase is thermodynamically more stable than the trigonal phase in a low temperature region, and the stability was reversed at about 225 K. This temperature corresponds to the phase transition point from the orthorhombic to trigonal phase, which is however considerably lower compared with the actually-observed transition point. The large discrepancy might be ascribed to the additional contribution of the entropy term due to the structural disorder and/or the thermal motion of chains with a large amplitude, which was not taken into account in the DFT calculation.

Influence of T5 Aging Heat Treatment on Microstructure and Mechanical Properties of as-extrued ZK80 Mg alloy

The micrstructure and mechanical properties of as-extruded ZK80 Mg alloy after artificial aging heat treatment was investigated. The results show that the hardness of the alloy first increases with the increase of time under different aging temperature, and then begins to decrease after reaching the peak value. Under the condition of the same aging temperature and different holding time, the hardness increases gradually with the increase of aging temperature, and then decreases with the increase of aging temperature. The best aging temperature of ZK80 Mg alloy is 180°C, the ultimate comprehensive mechanical properties of ZK80 alloy aging at 180°C for 7h reaches the maximum, which σb, σ0.2, δ, HBR, respectively is 326.7 MPa, 236.7 MPa, 10% and 77.8 HB, and the mechanical properties of untreated extruded state increased by 39.4%, 28.8% and 19%, respectively, The reason is that during the aging treatment, finely dispersed MgZn and MgZn2 phases are precipitated in the alloy structure, so that the mechanical properties of the extruded ZK80 magnesium alloy are optimized.

Relaxation properties of organo-mineral composites

The relaxation properties of hybrid organic-mineral composite materials based on liquid sodium glass, 2.4-toluendiisocyanate and the polyisocyanate, modified epoxy resin have been investigated. The aim of this work is to produce building materials, combining the properties of organic polymers and inorganic materials. Obtaining such materials in one stage creates the preconditions for energy savings and obtaining high quality materials. Curing in the mild conditions at temperatures of 60-70°C leads to the formation of network structures of the polymers. Methods: To characterize the mechanical properties used method stress relaxation. For polymers, the relaxation properties are not less important than the ultimate mechanical properties (strength and deformability). At constant strain, the stress relaxes intensively, resulting in loss of mechanical efficiency of the material. Measurement of stress relaxation at various temperatures gave the opportunity of creating master curves of relaxation and prediction of mechanical behavior for a long time. To study the chemical structure of the produced materials we used the method of IR spectroscopy. The outcome of the following: Spectral studies and related calculations using the computer program "Cascade" (INEOS RAS) indicate the complex nature of the chemical transformations during thermal exposure in preparing monolithic samples. Modification of the initial mixtures with epoxy resin results in a more homogeneous fine-grained structure of the composites and improving their mechanical properties. The study of the process of stress relaxation at various temperatures in the range 20-100°C were provided and the physical parameters of the memory functions were found. The initial relaxation modulus reached values of 1000 MPA at 20°C, and 540 MPa at 100°C. For free of non-modified epoxide starting materials of the relaxation module was 730 MPa at 20°C and at 100°C to 520. The master curves were drawn to predict relaxation behavior for large durations of the course of process. The greatest relaxation module has material containing an increased amount of a polyisocyanate. Conclusions: the resulting structures can serve as the basis of decorating and construction building materials. They are easily painted in different color, have moderate stress relaxation and high relaxation modules.

Polyvinyl alcohol reinforced with carbon nanotubes for fused deposition modeling

For the first time, nanocomposite filaments consisting of polyvinyl alcohol and carbon nanotubes were successfully used for additive manufacturing by fused deposition modeling. Polyvinyl alcohol and carbon nanotubes were mixed in a water solution using hexadecyl trimethyl ammonium bromide as a surfactant. Filaments with various concentrations of carbon nanotubes (up to a maximum content of 3 wt.%) were obtained with a single screw extruder and used to feed a commercial desktop 3D printer. Carbon nanotubes increase the glass transition temperature of the printed samples; however, the presence of CTAB reduces this effect. The viscosity of the material increases with the addition of carbon nanotubes and the 3D-printed samples become tougher as the carbon nanotubes amount increases. Elastic modulus and creep compliance are remarkably improved by the presence of carbon nanotubes, while ultimate mechanical properties are not affected. The high reduction of electrical resistivity found on the filaments was not found on the 3D-printed samples. This was attributed to the prevalent location of carbon nanotubes in the core region of the 3D-printed samples as documented by scanning electron microscopy.

Polyvinyl alcohol reinforced with crystalline nanocellulose for 3D printing application

The aim of this work is to produce fully biodegradable nanocomposite filaments with improved thermo-mechanical properties, to be used in fused deposition modeling (FDM) 3D printing process. At this aim, nanocomposites consisting of poly(vinyl alcohol) (PVOH) containing various amounts (from 2 to 20 wt%) of cellulose nanocrystals (CNC) were produced by solution mixing, grinded and extruded into filaments by a single screw extruder. The obtained nanocomposite filaments were then used to feed a desktop 3D printer.In both filaments and 3D printed specimens, CNC promoted a progressive enhancement of thermal stability manifested in an increase of the glass transition temperature measured by differential scanning calorimetry. Moreover, both dynamic storage and loss moduli were also increased proportionally to the filler content, and a positive reduction of the creep compliance was observed. For a CNC content of 10 wt% the creep compliance at a given loading time (one hour) decreased in both filament (by 47%) and in 3D printed samples (by 35%) in comparison to neat PVOH. Ultimate mechanical properties of filaments also increased with the introduction of CNC till 10 wt%, with a maximum reinforcement effect observed at 2 wt% of CNC for which an increase of 81% in the values of tensile energy to break and 45% in the stress at break were observed. An enhancement in tensile properties was observed also for 3D printed samples at 5 wt% of CNC for which the stress at break manifested an improvement of 73%. Adhesion between layers in 3D printed parts resulted to play a major role in the fracture behavior.

Variation of mechanical properties and oxidation with radiation dose and source in highly crosslinked remelted UHMWPE.

Ultra-high molecular weight polyethylene (UHMWPE) is the current gold standard for bearing materials used in total joint arthroplasty. High-dose radiation is commonly used to crosslink UHMWPE, thereby improving its wear resistance. A subsequent remelting step eliminates trapped residual free radicals to promote oxidative stability on the shelf, and to prevent material degradation over the long term. Assessment of clinically retrieved, highly crosslinked UHMWPE devices shows signs of unanticipated oxidation occurring in vivo, despite the absence of free radicals prior to implantation. These findings warrant further investigation into possible factors impacting this phenomenon along with its clinical implications. The overall objective of this work is to quantify the influence of irradiation dose and source on UHMWPE's oxidative stability, along with the effects of oxidation on the ultimate mechanical properties, including strength, ductility, and toughness. The results showed a strong positive correlation between maximum oxidation and initial transvinylene content. Critical oxidation levels in the context of mechanical property loss were determined for e-beam and gamma treatments at various radiation doses. Further, it was shown that critical oxidation was more dependent on radiation dose and less dependent on source. If in vivo oxidation persists in these devices, this can potentially lead to mechanical failure (e.g. fatigue damage) as observed in terminally gamma-sterilized devices.

Predicting Microstructure Evolution During Directed Energy Deposition Additive Manufacturing of Ti-6Al-4V

Laser engineering net shaping (LENS) is one of the representative processes of directed energy deposition (DED) in which a moving heat source having high-intensity melts and fuses metal powders together to print parts. The complex and nonuniform thermal gradients during the laser heating and cooling cycles in the LENS process directly affect the microstructural characteristics, and thereby the ultimate mechanical properties of fabricated parts. Therefore, prediction of microstructure evolution during the LENS process is of paramount importance. The objective of this study is to present a thermo-microstructural model for predicting microstructure evolution during the LENS process of Ti-6Al-4V. First, a detailed transient thermal finite element (FE) model is developed and validated for a sample LENS process. Then, a density type microstructural model which enables calculation of the α-phase fractions (i.e., Widmanstätten colony and basketweave α-phase fractions), β-phase fraction, and alpha lath widths during LENS process is developed and coupled to the thermal model. The microstructural algorithm is first verified by comparing the phase fraction results with the results presented in the literature for a given thermal history data. Second, the average lath width values calculated using the model are compared with the experimentally measured counterparts, where a reasonable agreement is achieved in both cases.

A Regression Method Based on Noninvasive Clinical Data to Predict the Mechanical Behavior of Ascending Aorta Aneurysmal Tissue.

Goal: Ascending aorta aneurysms represent a severe life-threatening condition associated with asymptomatic risk of rupture. Prediction of aneurysm evolution and rupture is one of the hottest investigation topics in cardiovascular science, and the decision on when and whether to surgically operate is still an open question. We propose an approach for estimating the patient-specific ultimate mechanical properties and stress-stretch characteristics based on noninvasive data. Methods: As for the characteristics, we consider a nonlinear constitutive model of the aortic wall and assume patient-specific model coefficients. Through a regression model, we build the response surfaces of ultimate stress, ultimate stretch, and model coefficients in function of patient data that are commonly available in the clinical practice. We apply the approach to a dataset of 59 patients. Results: The approach is fair and accurate response surfaces can be obtained for both ultimate properties and model coefficients. Conclusion: Prediction errors are acceptable, even though a larger patient dataset will be required to stabilize the surfaces, making it possible to apply the approach in the clinical practice. Significance: A fair prediction of the patient aortic mechanical behavior, based on clinical information noninvasively acquired, would improve the decision process and lead to more effective treatments.Goal: Ascending aorta aneurysms represent a severe life-threatening condition associated with asymptomatic risk of rupture. Prediction of aneurysm evolution and rupture is one of the hottest investigation topics in cardiovascular science, and the decision on when and whether to surgically operate is still an open question. We propose an approach for estimating the patient-specific ultimate mechanical properties and stress-stretch characteristics based on noninvasive data. Methods: As for the characteristics, we consider a nonlinear constitutive model of the aortic wall and assume patient-specific model coefficients. Through a regression model, we build the response surfaces of ultimate stress, ultimate stretch, and model coefficients in function of patient data that are commonly available in the clinical practice. We apply the approach to a dataset of 59 patients. Results: The approach is fair and accurate response surfaces can be obtained for both ultimate properties and model coefficients. Conclusion: Prediction errors are acceptable, even though a larger patient dataset will be required to stabilize the surfaces, making it possible to apply the approach in the clinical practice. Significance: A fair prediction of the patient aortic mechanical behavior, based on clinical information noninvasively acquired, would improve the decision process and lead to more effective treatments.

An experimental study of the effect of CNTs on the mechanical properties of CNTs/NR/EPDM nanocomposite

Carbon nanotube (CNT)/Natural rubber (NR)/ ethylene–propylene diene monomer (EPDM) nanocomposites were prepared via a traditional mixing method using a two‐roll mixer and cured by a conventional vulcanization system. The nanocomposites were characterized with respect to their curing characteristics and mechanical properties. The cure characteristic investigations showed that the introduction of CNTs into the rubber blend leads to a decrease in scorch and cure times. The minimum and maximum torque values of the cured nanocomposites rise with respect to CNTs loading. Tensile strength of NR/EPDM (75/25 wt/wt) blends containing 0.5 wt% of CNTs showed an increase compared to the NR/EPDM blends. The moduli of the nanocomposites at 100% and 300% elongations revealed that the CNTs can increase these parameters with no significant effect on the elongation at break. The stress–strain behavior of the nanocomposites was analyzed by some proper phenomenological hyperelastic models and the effect of CNTs loading on their material parameters was investigated. The introduction of CNTs into the NR/EPDM matrix leads to a significant change in material parameters of hyperelastic models. The results suggested that various CNTs loadings have a significant effect on the dispersion state of nanotubes and ultimate mechanical properties of CNT/NR/EPDM nanocomposites. POLYM. COMPOS., 39:4071–4079, 2018. © 2017 Society of Plastics Engineers

On the representative elementary size concept to evaluate the compatibilisation of a plasticised biopolymer blend

This study combines experimental and numerical approaches to investigate the microstructure and mechanical behaviour of non-miscible plasticised starch/zein blends. The concept of Representative Elementary Size (RES) is used to rank the effect of five different plasticisers (cholinium acetate, glycerol, butyl methyl imidazolium chloride, glycerol-choline chloride, urea-choline chloride) inducing microstructural and mechanical changes in the blends. Microstructural and mechanical RESs are derived from microscopy image analysis and Finite Element Modelling of elasticity behaviour of studied blends. Compared to the usual consideration of ultimate mechanical properties (elongation and stress at break), the RES-based approach allows detecting the presence of perfect or imperfect interface between starch and zein particles depending on the nature of plasticiser.

Study on the mechanical properties of the mortars exposed to the sulfate attack of different concentrations under the triaxial compression with constant confining pressure

The ingress of sulfate ion and mechanical load are two main reasons to induce the degradation of the properties in the marine structures. In this study, the mechanical properties of the samples exposed to sodium sulfate (Na2SO4) solution under the triaxial compression with three confining pressures were tested. Mohr-Coulomb, Willam-Warnke criteria were used to calibrate the mechanical properties of the sample. The concentration of Na2SO4 solution had no significant effect on the failure mode and the angle of the crack. The sample immersed in Na2SO4 solution of high concentration had a larger stress, a low strain, a fast increase rate in the mechanical properties and a short time to reach the ultimate mechanical properties at initial stage. Beyond an immersion time, sulfate attack of high concentration caused a rapid reduction in the stress, a low mechanical properties and strain. The increase of the confining pressure changed the failure mode, increased the angle of the crack. The sample in the high confining pressure had larger stress and mechanical properties, low strain. The cohesion in Mohr-Coulomb criterion had the relationships with the day of exposure and the concentration of Na2SO4 solution. The parameters in Willam-Warnke criterion were dependent on the immersion period.

Friction stir welding of aluminium alloys: An overview of experimental findings – Process, variables, development and applications

The never ending appetite of the mankind to produce more and more competitive products results in continuous development of newer and newer manufacturing processes. One of such a kind, a solid state welding process highly appreciated for joining of a variety of aluminium and copper alloys, is friction stir welding. The process is also an accomplished method for joining dissimilar materials efficiently. The process finds its major application for joining hard-to-weld metals, especially the precipitation hardenable aluminium alloys and is widely adopted by industries for the welding of such aluminium alloys. However, the process has still not found an economical way for welding of steels and hence found limited applications in industries for welding steels. This paper aims at providing a comprehensive review of the work undertaken in the field of friction stir welding and provides an insight into the friction stir welding of aluminium alloys. The article pays critical attention and analytical evaluation of classification of aluminium alloys, friction stir welding process parameters, the mechanical testing and properties of the friction stir welding joints, macrostructure and microstructure evolution during friction stir welding, friction stir welding defects and industrial applications of the process. The friction stir welding process variants are discussed as well. Special accentuation has been given to (i) effect of friction stir welding parameters on the microstructure evolved and thus the ultimate mechanical properties (viz. tensile strength, hardness, fatigue strength, fracture toughness and residual stresses), (ii) the texture formation, microstructure refinement and the role of intermetallics. However, studies related to welding of dissimilar aluminium alloys, temperature, and heat transfer modeling and material flow are out of the scope of this paper. Finally, the directions of future research are examined.

Structure and properties of gel-spun ultra-high molecular weight polyethylene fibers with high gel solution concentration

The gel-spun ultra-high molecular weight polyethylene (UHMWPE) fibers were prepared at the industrial production line with different gel solution concentrations of 15 wt%, 18 wt% and 24 wt%. The difference in ultimate structure and mechanical properties of UHMWPE fibers for different gel solution concentrations were analyzed by tensile testing, differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). With the increase of gel solution concentration, the ultimate mechanical properties of UHMWPE fibers were decreased and the crystallization and orientation of UHMWPE fibers became inferior. Besides, both the average shish length (<L shish>) and shish misorientation (B ϕ ) of UHMWPE fibers were decreased with the increase of gel solution concentration. In addition, the appropriate increase of spinning temperature led to the further optimization of the ultimate structure and mechanical properties of UHMWPE fibers.

The Abnormal Architecture of Healed Diabetic Ulcers Is the Result of FAK Degradation by Calpain 1

Delayed wound healing is a major complication of diabetes occurring in approximately 15% of chronic diabetic patients. It not only significantly affects patients' quality of life but also poses a major economic burden to the health care system. Most efforts have been focused on accelerating wound reepithelialization and closure. However, even after healing the quality of healed tissue in diabetics is abnormal and recurrence is common (50-75%). Thus, understanding how diabetes alters the ultimate mechanical properties of healed wounds will be important to develop more effective approaches for this condition. Focal adhesion kinase is an intracellular protein kinase that plays critical roles in cell migration, focal adhesion formation, and is an important component of cellular mechanotransduction. We have found that focal adhesion kinase expression is downregulated under a high glucose condition both invitro and invivo. This is secondary to increased activity of calpain 1, the primary enzyme responsible for focal adhesion kinase degradation, which becomes induced in hyperglycemia. We demonstrate that selective inhibition of calpain 1 activation improves wound healing and normalizes the mechanical properties of diabetic skin, suggesting a new therapeutic approach to prevent diabetic wound recurrence.

Significant influence of carbon and niobium on the precipitation behavior and microstructural evolution and their consequent impact on mechanical properties in microalloyed steels

Carbon and niobium (Nb) play an important role in influencing the ultimate microstructure and mechanical properties. In this regard, we elucidate here the impact of carbon and Nb on the microstructural evolution and precipitation behavior during continuous cooling of industrially processed microalloyed steels with varying carbon and Nb-content. The microstructure and precipitation evolution was studied via electron microscopy and related to the outcome of thermodynamic simulation. The increase of carbon content in steel increased the precipitation temperature of (Nb, Ti)(C, N), which led to relatively larger size (Nb, Ti)(C, N) precipitates. Furthermore, high carbon content contributed to stabilization of austenite and delayed the transformation of ferrite and bainite, such that martensite/austenite content (M/A) was obtained. The M/A islands in high carbon-containing steel contributed to highest strength and intermediate elongation. The high degree of (Nb, Ti)(C, N) precipitation in steel contributed to refinement of prior austenite grain size and strain accumulation, which increased ferrite and bainite start transformation temperature, resulting in higher volume fraction of polygonal ferrite. Polygonal ferrite in steel with high Nb-content was responsible for relatively low strength in comparison with steels with higher carbon or intermediate carbon-Nb contents. Granular bainite and lath bainite in steel with intermediate C and Nb-contents was characterized by best combination of strength and elongation. The outcomes of the thermodynamic simulations were consistent with the experimentally observed microstructure.

Practical Use of Computer Model STAN 2000 for Improvement and Creation of Regimes for Hot Rolling of Steels on SEVERSTAL Mill 2000

An integral computer model STAN 2000 designed for of-line simulation and control of hot rolling on mill 2000 of SEVERSTAL was developed. The capabilities of the model include the following features: ‒ calculations of power parameters for all stands of mill 2000 for a given rolling schedule; ‒ strip temperature calculations depending on selected rolling and accelerated cooling regimes; ‒ follow-up of steel microstructure evolution at all stages of strip production and prediction of ultimate mechanical properties (yield stress, ultimate tensile stress, relative elongation and toughness); ‒ optimization of rolling regimes for existing steel grades and developing them for a new one. The STAN 2000 program is written in С++ programming language and can work on all modern Microsoft Windows family operating systems. The program has a well-designed and user-friendly interface facilitating its practical use. The integral model was calibrated using an extensive data base on rolling regimes and forces, measured temperatures and final mechanical properties for a number of steel grades rolled on mill 2000 of SEVERSTAL with chemical compositions covering the following range of alloying elements content (mass.%): С(≤0.65); Mn(≤2.0); Si(≤1.0); Cr(≤0.9); Ni(≤0.6); Cu(≤0.5); Mo(≤0.4); Nb(≤0.05); V(≤0.065); Ti(≤0.06); B(≤0.003). The examples of STAN 2000 program use in practice of industrial hot strip production on mill 2000 of SEVERSTAL are presented and discussed.

Characterization of polyoxymethylene for backsheets of photovoltaic modules

This article describes and evaluates the basic properties and the damp heat (85%RH, 85℃) aging behaviour of a 400 µm thick titanium dioxide filled polyoxymethylene film for potential use as backsheet in photovoltaic (PV) modules. The polyoxymethylene monolayer was characterized using analytical methods and technological tests. The stabilizer package contained Tinuvin 234, Tinuvin 770 and Irganox 245. The less than 1 wt% pigmentation resulted in 0.680 solar optical reflectance. The slightly anisotropic mechanical properties elastic modulus and strength were within the requirements for backsheets. Damp heat exposure triggered degradation, stabilizer loss and lead to optical properties degrading (yellowing). However, neither premature embrittlement nor a critical loss of ultimate mechanical properties was found after 5005 h of aging. Hence, polyoxymethylene was classified as a potential candidate for backsheet core layers.

Effect of Gel Solution Concentration on the Structure and Properties of Gel-Spun Ultrahigh Molecular Weight Polyethylene Fibers

The gel-spun ultrahigh molecular weight polyethylene (UHMWPE) fibers were prepared at the industrial production line with different gel solution concentration of 10–18 wt %. The effect of gel solution concentration on the structure and performance of UHMWPE fibers was studied by tensile testing, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). With the increase of gel solution concentration, the ultimate mechanical properties of UHMWPE fibers decreased while the melting temperature increased. And the increase of gel solution concentration made the crystallization and orientation of UHMWPE fibers become worse. Furthermore, the average length (⟨Lshish⟩) and misorientation (Bϕ) of shish structure in UHMWPE fibers decreased with the increase of gel solution concentration.

Impact of Innovative Cooling System on Mechanical Properties of Moulded Parts

This article deals with the impact evaluation of utilization of innovative cooling system exploiting liquid carbon dioxide injected into injection mould. Process of heat transfer from the polymeric melt and final part solidification has a direct impact on creation of morphology structure of semi-crystalline thermoplastic materials and their ultimate mechanical properties. Usually the heat processes in the production tools are controlled by tempering channels where heat transfer medium circulates (oil, water tec.). This conventional way of cooling has some limitations that cause an uneven distribution of temperature fields on the part surface. Spot cooling system is one of unconventional cooling ways that increase the uniformity of temperature fields distribution on the part surface. This system utilizes the cooling potential of liquid CO2. For the purpose of this study the special shaped insert was designed that was modified both for conventional cooling and for spot cooling system. Flexural modulus very responsively reflects the changes of morphology structure formed by different cooling progressions of the plastic melt and was chosen as an evaluating criterion.

Processing-structure-mechanical property relationship in Ti-Nb microalloyed steel: Continuous cooling versus interrupted cooling

The process parameters associated with thermo-mechanical controlled processing (TMCP) of steels play an important role in influencing the ultimate mechanical properties. The study of TMCP parameters have not received the required attention. In this regard, we elucidate here the impact of finish cooling temperature on interrupted cooling and compare with continuous cooling on microstructural evolution and precipitation behavior and associated mechanical properties in Ti-Nb microalloyed steels. The microstructural evolution was studied via transmission electron microscopy and electron back scattered diffraction (EBSD). The microstructure of continuously cooled and interrupted cooled steels with different finish exit temperatures consisted of polygonal ferrite, bainite and martensite/austenite constituent. However, the fraction of different microstructural constituents was different in each of the experimental steels. Similarly, there were differences in the distribution and average size of (Nb, Ti)C precipitates. The aforementioned differences in the microstructure and precipitation introduced differences in tensile properties. Furthermore, electron back scattered diffraction studies indicated distinct variation in average grain area and high angle boundaries between continuously cooled and interrupted cooled steels.