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Outdoor building materials made of wood require preservatives containing chromated copper arsenate and other carcinogenic substances but still are subject to decay, hence they need to be replaced every few years. Wood-plastic composite (WPC) is an environmental-friendly composite of wood flour/fiber reinforced thermoplastic polymers (i.e., plastic). As WPC is made of plastic to evenly cover the wood flour, it has a lower moisture content than wood. In this study, maleic anhydride grafted polyolefin elastomers (POE-g-ma) and methyl methacrylate-butadiene-styrene copolymer (MBS) were used as impact modifiers to prepare WPCs from recycled polyethylene terephthalate (rPET) and recycled polyamide 6 (rPA6) blends (PET/PA6). The thermal properties of the WPCs with different mixing ratio polymer blends of rPET to rPA6 (E60/A40, E50/A50, and E40/A60) were investigated, as well as their mechanical properties after accelerated weathering. In addition, the creep behavior of the E40/A60 WPC under different environmental conditions was investigated. During the 10-h creep test, the POE-g-ma/WPC strain varied significantly more than MBS/WPC under environmental aging and higher loadings. The test results of impact and creep also show that the toughening effect of POE-g-ma/WPC was slightly better than that of MBS/WPC. In summary, the higher PET content resulted in lower flowability and a higher initial decomposition temperature, with the E60/A40 WPC having better anti-aged mechanical properties and more suitable for outdoor building applications.

In this study, a meshless numerical method for 2D problems with 2 variables coupled together in 2 partial differential equations (PDEs) is proposed. This method employs the local polynomial approximation with the weighted-least-squares (WLS) approach. A very distinguishing feature of this method from other collocation methods is the governing equations are satisfied at boundary nodes as well as the boundary conditions. By doing so the strong-form collocation method would be more stable. The 2D elasto-statics analysis is chosen for demonstrating the performance. Three test cases are implemented and the results are compared with exact or analytic solutions. Very good agreements are found.

In this study, the effect of wall thickness (15&ndash, 25 mm) on the stress&ndash, strain response of hollow-cylinder rubber fenders were investigated by conducting monotonic compression tests. It was found that a progressive increase in lateral bending deformation was observed during monotonic compression. Simultaneously, the extent of the lateral deflection decreased notably with an increasing wall thickness. From the experimental results, the fact is accepted that buckling occurred in the tested fender due to the fact that the ratio of the height to the wall thickness was higher than four in all of the considered cases. Moreover, an s-shape profile appeared in the stress&ndash, strain curves, which became clearer as the wall thickness was reduced from 25 to 15 mm. To assess the performance of fenders objectively, an energy-effectiveness index, C E R , was introduced to quantify the energy absorption capacity of the fender. From the experimental observations, it was inferred that the contact area of the folded inner surface of the fender produced under compression generated an additional reaction force and affected the shape of the stress&ndash, strain curve since the measured load consisted of two reaction forces: one caused by the self-contact area, and the other resulted from the compression-bending deformation that occurred in the side wall of the fender. To examine this assertion, a finite element analysis (FEA) was conducted and confirmed the effect of the reaction force on the sensitivity of the s-shape characteristic of the stress&ndash, strain curve. Finally, a polynomial regression was conducted and the calculated results based on the fourth-degree stress polynomial function correlated very well with the measured stress&ndash, strain curves.

Anisotropic conductive film (ACF), is a lead-free material that is commonly used in fine-pitch interconnect manufacturing to make and maintain the electrical and mechanical connections between the micro-electrodes. A key issue about the circuit conductivity is the deformation, breakage, and number of conductive particles in the ACF packaging. For the field of vision, the Film-On-Glass (FOG) assembly on the glass-side is used to obtain excellent images in experimental observation. This paper utilizes the microscope technology to investigate the bonding properties of the conductive particles, and consider the electrical resistance effects after packaging. The results show the deformation shape, breakage type, and number of conductive particles will be quantitatively affect the electrical performances, and one can measure the area, diameter, and roundness of the deformed particles’ projection in the glass-side view to evaluate the ACF packaging quality.

A series of fatigue tests with type I and type II cycle damage histories were carried out to observe the effects of pre-cycle damage on the subsequent cyclic material response and fatigue resistance. It was found that the applied cycle history of damage leads to an increase in the extent of variation in cyclic hardening/softening. Furthermore, the shape of stable hysteresis loop changes with the type of cycle damage history under the same strain amplitude conditions. This is due to the occurrence of additional cyclic hardening/softening. By comparing the strain–life curves with and without a cycle damage history, it is found that the cycle damage history leads to a decrease in the number of cycles to failure. The loss in fatigue resistance is dependent on the type of pre-cycle damage history. For the fatigue test with a pre-cycle history, an equivalent cycle ration C 1 ⁎ is proposed to predict the residue cycles at the second level in this study. The validity of the modified expression is confirmed by comparing the predicted life results with the corresponding experimental data. It is apparent that the proposed method gives a better prediction than the Miner׳s rule for the two-step histories.

In this study, graphene nanoplatelet (GNP)/nano-carbon aerogel (NCA) hybrids were used to reinforce epoxy resin and epoxy/carbon fiber composite (CFRP) laminates in order to investigate the synergistic effects on their mechanical properties. The GNP/NCA hybrids (1 wt%) with different mixing ratios (i.e., 10:0, 9:1, 7:3, 5:5, and 3:7) were dispersed in epoxy resin to prepare GNP/NCA/epoxy nanocomposites. The mechanical properties such as ultimate tensile strength, flexural strength, flexural modulus, and impact strength of these nanocomposites were investigated. Additionally, the fracture surfaces of the specimens examined using field-emission scanning electron microscopy and transmission electron microscopy to determine the dispersal mechanisms of the GNP/NCA hybrids in the epoxy resin.A 3k carbon fiber fabric impregnated with different amounts (i.e., 0, 0.25, 0.5, 0.75 and 1.0 wt%) of GNP/NCA epoxy resin, and epoxy/CFRP laminates was prepared using a fixed mixing ratio of 5:5. The synergistic effect of the GNP/NCA hybrid on the mechanical properties of the carbon-fiber-reinforced epoxy resin composite laminates was also investigated.The experimental results demonstrate that the mechanical properties of GNP/NCA/epoxy nanocomposites and GNP/NCA/CFRP laminates are optimized via reinforcement upon the addition of GNP/NCA hybrids. Keywords: Graphene nanoplatelets (GNPs), Nano-carbon aerogels (NCAs), Hybrids, Synergistic effect, GNP/NCA/epoxy nanocomposite, Epoxy/carbon fiber composite (CFRP) laminates, Mechanical properties

The study was devoted to the observation and modeling the mechanical behaviors of a hybrid SBR/NR (Styrene-Butadiene/Natural Rubber) hybrid vulcanized rubber fender under monotonic/cyclic compression. In experimental observations of the monotonic compression tests, it was found that lateral deformation occurred on the tested fender and was more significant with increasing the extent of the compressive strain. The relationship between the transmission stress S c and the compressive strain e c was nonlinear and the absorbed strain-energy-density was increased monotonically with the increment of the compressive strain. Among all cyclic compression tests with strain controlled, the reductions in both the stress range and the absorbed strain-energy-density up to the ten-thousandth cycle were found and then both of the cyclic properties remain approximately constant in the following compression cycles. Two new properties, the softening factor and the energy reduction factor, were introduced to quantify the effect of the strain range on the extent of the reduction in stress range and that on the absorbed strain-energy-density, respectively. It was found that both of the calculated values of the new properties increase with the increment of strain range. In mathematical modeling of the relationship between the transmission stress and the compressive strain, a new approach based on energy-polynomial-function E s ( e c ) was presented and was successfully used to simulate the monotonic curve and the stable hysteresis loop curves of the tested rubber fender in compression. Essentially, the energy-polynomial-function E s ( e c ) was obtained by performing a polynomial regression on a large amount of ( e c , E s ) data. Moreover, the least-square approach was applied to determine the corresponding regression coefficients in E s ( e c ) . Clearly, the stress-polynomial-function in modeling the S c &minus, e c curve could be obtained from the differentiation of the energy-polynomial-function with respect to the compressive strain. In addition, to provide an adequate estimation of the mechanical properties of the cylindrical rubber fender under compression, the named cyclic stress-strain curve and cyclic energy-strain curve were developed and also modeled in this study.

In this paper, the effects of tensile pre-deformation on material properties and fatigue life are investigated. For this purpose, a series of tensile fracture tests and fully reversed cyclic mode load-controlled tests have been performed on the tested 430 Stainless Steel in as-received condition and for the same tested material pre-strained at room temperature. Tensile pre-strain, , conditions were induced at three levels: 5%, 8%, and 12%. Experimental observations on tensile properties, fatigue strength coefficient, and exponent were done and are represented in this study. Empirical formulas were developed in polynomial form to estimate the tensile properties in pre-strained condition. Meanwhile, in this study, two empirical relationships for estimating fatigue strength coefficient and exponent using ultimate strength have been proposed and the corresponding approximation of S–N curves based on the Basquin equation form have been developed. The approximation of the S–N curve has provided good predictions...

The purpose of this study is to investigate the fatigue behavior of the SUS 430 Stainless Steel after the tensile pre-deformation is subjected to a symmetric loading. The investigations have been performed in three levels of pre-deformation. Cyclic deformation following pre-deformation was carried out in tension-compression fatigue test experiment at room temperature. The pre-deformation was induced on the specimen by a tensile test under strain control at 5%, 8%, and 12% strain level at a strain rate of 10−4s−1, respectively. In this paper, the effects of the cyclic deformation behaviors with different pre-strain levels were compared with the fatigue responses without pre-strain. Based on the comparison, it is found that the pre-strain caused evident changes in fatigue behaviors such as cyclic softening response, cyclic creep response, and cycles to failure. Generally, as compared to the as-received material, the softening response increased with increasing pre-strain level. A pronounced cyclic compressive creep occurred in the specimen with and without pre-strain level effect in all applied loading cases. This could be attributed to an-isotropy between tension and compression, resulting in the occurrence of compressive cyclic creep on the tested material during cyclic loading. Moreover, the stable total compressive creep strain scaled with increasing tensile pre-strain level for same cyclic loading. For the effect of pre-strain on fatigue resistance, a decrease in the number of cycles to failure was observed and the extent of the decrease also increased with increasing tensile pre-strain level under the same loading amplitude condition. In this paper, three damage parameters, ΔWp, Wf, and σaεa, are respectively used to predict the number of cycles to failure of the tested material with tensile pre-strain effect. In the plot of observed versus predicted cycles, it is observed that most of the data points are located within the bound of factor two for the three damage parameters. Consequently, it is confirmed that the three damage parameters could provide satisfactory predictions for the tested material with a tensile pre-strain effect.

Failure modes of swept spot friction welds in lap-shear specimens of alclad 2024-T3 aluminum sheets are first investigated based on experimental observations. Optical and scanning electron micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. Experimental results show that the failure modes of the welds under quasi-static and cyclic loading conditions are quite different. Failure modes of swept spot friction welds depend considerably on the weld geometry, microstructure, and load amplitude. A fatigue crack growth model based on the paths of the dominant kinked fatigue cracks is developed to estimate the fatigue lives of the spot friction welds. The global and local stress intensity factors for finite kinked cracks, the stress intensity factors for finite transverse cracks, and the Paris law for fatigue crack propagation are used. The fatigue life estimations agree well with the experimental results.

In the analytic solution of residual stresses and bending in multi-layer/substrate systems, Young's modulus of contact-etch-stop layer (CESL) stressor is a potential factor affecting the channel stress of complementary metal–oxide–semiconductor (CMOS) devices. To increase the level of Young's modulus of CESL stressor, the stress level of silicon channels could be boosted at a constant stress level and thickness of CESL as the result of stress simulation. Young's moduli of two widely adopted CESL stressors measured by a nanoindenter instrument, low-pressure chemical vapor deposition silicon nitride (LP-SiN) and plasma-enhanced chemical vapor deposition silicon nitride (PE-SiN), were 375.7 and 224.7 GPa, respectively. As a result of stress stimulation, the channel stress induced by LPSiN CESL could increase 30% higher than that of PE-SiN CESL. Through the use of a tensile 1 GPa CESL stressor for the 90 nm n-FETs, an extra 4% enhancement in drive current ID,sat was obtained in the device with an LP-SiN CESL as compared to that with PE-SiN. The electrical data is in good agreement with the prediction of the stress simulation.

This paper develops an analysis procedure to study the effects of intermetallic compound (IMC) growth on the fatigue life of 63Sn–37Pb (lead-rich)/96.5Sn–3.5Ag (lead-free) solder balls for flip-chip plastic ball grid array packages under thermal cycling test conditions. In this analysis procedure, the thickness of the IMC increased with the number of thermal cycles, and was determined using the growth rate equation. A series of non-linear finite element analyses was conducted to simulate the stress/strain history at the critical locations of the solder balls with various IMC thicknesses in thermal cycling tests. The simulated stress/strain results were then employed in a fatigue life prediction model to determine the relationship between the predicted fatigue life of the solder ball and the IMC thickness. Based on the concept of continuous damage accumulation and incorporated with the linear damage rule, this study defines the damage of each thermal cycle as the reciprocal of the predicted fatigue life of the solder joints with the corresponding IMC thickness. The final fatigue failure of the solder ball was determined as the number of cycles corresponding to the cumulative damage equal to unity. Results show that the solder joint fatigue life decreased as the IMC thickness increased. Moreover, the predicted thermal fatigue life of lead-rich solders based on the effects of IMC growth is apparently smaller than that without considering the IMC growth in the reliability analysis. Results also show that the influence of the IMC thickness on the fatigue life prediction of the lead-free solder joint can be ignored.

The crack behavior of the intermetallic compounds (IMCs) for the solder joints of electronic packages under the thermal cycling test conditions was analyzed using the finite element method in this research. A flip-chip plastic ball grid array package was selected as the analysis target. The two-dimensional in-elastic finite element method was employed to calculate the fracture mechanics parameters at the crack tip; such as the modes I and II stress intensity factors. Two locations were considered herein to initiate the crack: the first one was on the interface between the IMC and the copper pad (interfacial cracks); and the other one was at the inner part of IMC (IMC cracks). Furthermore, the effects of crack length and thickness of IMC on the crack tip parameters were also studied in this investigation. In the numerical simulation, the properties of the solder joint and the underfill were assumed to be elastic–plastic–creep and viscoelastic, respectively. The sub-modeling technique was used in the finite element analysis to reduce the computational time and the crack tip parameters were obtained using the simulated results of the displacement field near the crack tips. The results show that for both interfacial cracks and the IMC cracks, the modes I and II SIFs decrease as the length of crack increases, and the decreasing trend becomes more stable when the cracks propagate longer except for the variation of the mode II SIF for IMC cracks. Furthermore, the thickness of the IMC has slight effect on the magnitudes of SIFs under the conditions of constant crack lengths.

In this paper, the effect of the tensile pre-strain on ratcheting process in 430 Stainless Steel was examined by performing a series of fully tensile–compression cyclic loading tests on the tested material with three tensile pre-strain levels or no prior deformation. The experimental results indicate that a compressive cyclic creep occurs in all applied cases for the tested material without pre-strain. Clearly, the observation reflects that the tested material exists the an-isotropic in tension and compression. Furthermore, for the tested material with various value of pre-strain, cyclic creep can also be found and the direction of creep deformation is always opposite to that of the given pre-strain. From an experimental observation on the residue deformation produced by cyclic creep, it is found that the stable total compressive creep strain scaled with increasing tensile pre-strains at the same stress amplitude condition. The material with greater compressive creep strain responded to the same applied tensile pre-strain level with higher controlled stress amplitude. Exploring the effects of the tensile pre-strain on the stable stress–strain response, this paper has been focused on those items. They are the strain range, Δ e , plastic strain range, Δ e p , and plastic strain energy density, Δ W P at half-life. Experimental results show that the material with different tensile pre-strains or without pre-strain had a higher response when the applied stress amplitude range was increased. Those indicated material responses have increased at increasing tensile pre-strain. In observation the effects of tensile pre-strain on the fatigue, it is found that the effect of the tensile pre-strain is to reduce the cycles to failure. A decreasing fatigue life is observed with increasing the tensile pre-strain level. In the domain of high-cycle fatigue life (in the range of 10 5 –10 7 cycles), the effect of tensile pre-strain on degrading fatigue life is obvious and the degree of reducing fatigue life is governed by the magnitude of the stress amplitude. Moreover, the damage parameter based on the total plastic strain energy, W f = ∑ Δ W p , can produce satisfactory life prediction results for 430 Stainless Steel with a tensile pre-strain effect under fully reversed tension–compression loading condition.

In this paper, experiments of asymmetrical axial cyclic straining were conducted to explore the mean strain effects on the stable hysteresis loop and the fatigue life of AISI 304 stainless steel. The experimental results show that the imposed mean strain level has almost no influence on the shape of a stable hysteresis loop under the same strain amplitude condition. In terms of the mean strain effect on the fatigue life, at a strain amplitude greater than 0.6%, the imposed mean strain level was found to have no significant effect on the fatigue life, whereas a prominent effect on the fatigue life was found at low strain amplitude. Moreover, the endochronic theory of plasticity has been utilized to develop the stress–strain relationships to simulate the stable hysteresis curve in tension. A good agreement exists between the simulation curve and the experimental data. In this study, the fatigue damage parameter ( Δ W P ) T is applied to the predictions of fatigue life. The prediction life is obtained by the ( Δ W P ) T damage parameter calculated on the basis of the simulated hysteresis loop which has a good correlation with the experimental life.

This paper employs static atomistic simulations to investigate the effect of a void on the nanoindentation of Cu(111). The simulations minimize the potential energy of the complete system via finite element formulation to identify the equilibrium configuration of any deformed state. The size and depth of the void are treated as two variable parameters. The numerical results reveal that the void disappears when the indentation depth is sufficiently large. A stress concentration is observed at the internal surface of the void in all simulations cases. The results indicate that the presence of a void has a significant influence on the nanohardness extracted from the nanoindentation tests.

The stress induced in a workpiece under nanocutting are analyzed by an atomic-scale model approach that is based on the energy minimization. Certain aspects of the deformation evolution during the process of nanocutting are addressed. This method needs less computational efforts than traditional molecular dynamics (MD) calculations. The simulation results demonstrate that the microscopic cutting deformation mechanism in the nanocutting process can be regarded as the instability of the crystalline structure in our atomistic simulations and the surface quality of the finished workpiece varies with the cutting depth.

This study extends the plastic strain energy approach to predict the fatigue life of AISI 304 stainless steel. A modified energy parameter based on the stable plastic strain energy density under tension conditions is proposed to account for the mean strain and stress effects in a low cycle fatigue regime. The fatigue life curve based on the proposed energy parameter can be obtained directly by modifying the parameters in the fatigue life curve based on the stable plastic strain energy pertaining to fully reversed cyclic loading. Hence, the proposed damage parameter provides a convenient means of evaluating fatigue life on the mean strain or stress effect. The modified energy parameter can also be used to explain the combined effect of alternating and mean strain/stress on the fatigue life. In this study, the mean strain effects on the fatigue life of AISI 304 stainless steel are examined by performing fatigue tests at different mean strain levels. The experimental results indicate that the combin...

This study develops an analytical expression to describe the cyclic stress‐strain curve obtained from a series of fully‐reversed fatigue tests. A set of stress‐strain relationships is proposed to simulate the tensile branch of the stable hysteresis loop. The complete shape of the stable hysteresis loop is then constructed and the associated theoretical plastic work calculated by integrating the area within the enclosed curve. The theoretical plastic work is employed to predict the fatigue lives of the investigated materials on the basis of their respective stable plastic work per cyclelife curves. In this paper, the current mathematical derivations are based upon the endochronic theory of plasticity. The accuracy of the proposed set of stress‐strain relationships is verified by conducting fully‐reversed constant strain amplitude fatigue tests on AISI 316 and AISI 304 stainless steels. The experimental and simulation results are found to be in good agreement, hence confirming the accuracy of the p...