Effect Of Strain Level Research Articles

Effect of strain level on the cyclic response and microstructure characteristics of selective laser melted 304L

Considering the relationship between austenite stability and strain level, the cyclic response curves are obtained for SLM 304L under different strain amplitude at R = 0.3. The results indicate that since the microstructure characteristics shift from stacking faults (SFs) at low strain amplitude to martensite and twins at high strain amplitude, the cyclic softening behavior transitions to cyclic hardening behavior. Besides, it also indicates that high strain levels can overcome the influence of initial microstructure on fatigue performance, presenting a new sight to understand the relationship between cyclic hardening and martensite transformation.

Assessment of the influence of stitching on the tensile stress relaxation of laminated fabrics

Different parts of the garment may be laminated with an interlining in order to obtain specific appearance and form. Mechanical properties of the laminated fabric is affected by the properties of interlining and differs from the face fabric. Moreover, the existence of seam for joining the laminated fabrics in various parts of the garment is another issue, which has to be considered during the evaluation of the mechanical behavior of garment. Garments’ time dependent mechanical behavior such as the tensile stress relaxation is of great importance while wearing them. In this study, the tensile properties and the stress relaxation of a group of woven fabric, which was laminated by a nylon interlining, were investigated at two strain levels, before and after stitching. In this regard, the effects of strain level, lamination process, seam type and the stitch length were evaluated. According to the results, it can be declared that increasing the strain level reduces the stress relaxation percentage. The laminated fabric presented higher values of tensile stress and strain, while lower stress relaxation was occurred in this structure compared to the un-laminated fabric. Analysis of results showed that higher stress relaxation was obtained for the “stitched laminated fabric” compared to the “laminated fabric without seam.” Overall, in the presence of seam, the stress relaxation is affected by the seam type and the stitch length. Finally, the best correlation between the experimental stress relaxation results and the viscoelastic models were obtained for the two-component Maxwell model. The result of this study should be considered in designing and manufacturing of protective textiles and clothing that include both lamination and stitching processes and during use may be encountered with constant strains for a period of time.

On the evolution of microstructure, texture and corrosion behavior of a hot-rolled and annealed AZ31 alloy

The microstructure and texture evolution of an AZ31 alloy were investigated after hot rolling and subsequent annealing using electron backscatter diffraction (EBSD). First, the alloy was hot-rolled at 350 °C up to low, medium and high strain (20, 50 and 85% of thickness reduction, respectively). The alloy samples where then annealed at 350 °C for 2, 10 and 60 min. The effect of strain level and annealing on corrosion behavior in seawater was also evaluated using electrochemical tests. At low strain, the microstructure was characterised by the absence of twinning, mainly due to the prior thermo-mechanical history of the as-received alloy. However, various modes of twinning were observed at medium strain. At high strain, the dynamic recrystallization process resulted in a microstructure with a typical basal texture. The results demonstrate that twins are responsible for the deviation of {0002} basal poles from normal towards the transversal direction. Annealing at 350 °C for up to 60 min led to normal grain growth in all the samples. In medium and highly strained samples, the deformation texture was retained, while the low strain sample underwent noticeable changes due to the absence of dynamic recrystallization. A synergetic effect of grain refinement and texture weakening was responsible for the alloy's enhanced corrosion resistance.

Effect of strain level on strength evaluation of date palm fiber-reinforced sand

Conventional researches on the behavior of fiber-reinforced and unreinforced soils often investigated the failure point. In this study, a concept is proposed in the comparison of the fiber-reinforced with unreinforced sand, by estimating the strength and strength ratio at different levels of strain. A comprehensive program of laboratory drained triaxial compression test was performed on compacted sand specimens, with and without date palm fiber. The fiber inclusion used in triaxial test specimens was form 0.25%-1.0% of the sand dry weight. The effect of the fiber inclusion and confining pressure at 0.5%, 1.0%, 1.5%, 3.0%, 6.0%, 9.0%, 12%, and 15% of the imposed strain levels on the specimen were considered and described. The results showed that, the trend and magnitude of the strength ratio is different for various strain levels. It also implies that, using failure strength from peak point or the strength corresponding to the axial strain of approximately 15% for evaluating the enhancement of strength or strength ratio, due to the reinforcement, may cause hazard and uncertainty in practical design. Therefore, it is necessary to consider the strength of fiber-reinforced specimen at the imposed strain level, compared to the unreinforced specimen.

Effect of strain level on the evolution of microstructure in a recently developed AD730 nickel based superalloy during hot forging

Design and control of microstructure of engineering parts made from nickel based superalloys with superior mechanical properties for high temperature applications, require the parts to be subjected to certain thermo-mechanical processing during forging. This often includes sequential straining and annealing at elevated temperatures followed by subsequent aging heat treatments at lower temperatures. In this study, the effect of strain magnitude on the evolution of microstructure during hot forging of a recently developed AD730 nickel based superalloy has been investigated. Microstructural heterogeneity was observed in a forged material manifested in a form of large non-recrystallized grains within the recrystallized matrix that is observed to be dependent on the level of deformation (i.e. strain magnitude). Analyses of microstructure indicated significant reduction in the fraction of low-angle grain boundaries and sub-structures with an increase in the applied strain, suggesting higher fraction of recrystallization with higher levels of strains. It was concluded that the lower strain levels were insufficient to provide enough driving force for complete recrystallization throughout the entire microstructure of the forged material.

Effect of strain level on corrosion of stainless steel bar

This paper presents an experimental investigation into the corrosion of stainless steel bar in the stressed state. By performing an electrochemical accelerated corrosion test on S11203 stainless steel bar under different strain levels and a tensile test on corroded stainless steel bar, effect of strain level on corrosion of stainless steel bar was investigated. The experimental results indicated that strain level affected the degree of corrosion of stainless steel bar. The higher the strain, the higher the degree of corrosion. The degree of corrosion of stainless steel bar under a strain of 1.0 × 10−3 was 9 percent higher than that of under zero strain. With increase of the degree of corrosion, the yield strength, ultimate strength and elongation of stainless steel bar gradually degenerated, and especially significant for the degradation of elongation. It was also found that the influence of strain level (≤1.0 × 10−3) on corrosion morphology and mechanical properties of stainless steel bar within 15% corrosion degree was not significant.

Effect of strain level on stress relaxation and recovery behaviors of isotactic biaxially oriented polypropylene films

ABSTRACTThe long‐term recovery process and the changes in the uniaxial tensile properties and in the structure of isotactic biaxially oriented polypropylene (i‐boPP) films after pre‐extended at strain levels ranging from 1% up to 130% at room conditions were examined by using tensile testing, Fourier transform infrared spectroscopy/attenuated total reflectance, atomic force microscopy, and X‐ray diffraction methods. It is significantly observed that the pre‐extended i‐boPP films at strain levels from 1% to 6% recovered completely back to their initial lengths and tensile properties. However, the i‐boPP films showed a very slow recovery process and obtained very high remaining deformations changing with time which indicates irreversible structural processes after they were extended at higher strain levels. In order to predict the remaining deformation or length and the characteristics of the recovery process at any time, the linear equation of strain with respect to log time was proposed. The reasons for the changes in the tensile properties, the morphology, and the structure of the pre‐extended i‐boPP films were examined in detail. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42948.

Effect of Strain Level on the Behavior of Intermetallics and Texture of Al-Si-Cu-Mg Alloy Modified with Transition Metals

T uniaxial compression test was used to assess an influence of strain amount on the behavior of precipitates and texture of the Al-7%Si-1%Cu-0.5%Mg alloy, modified with micro-additions of V, Zr and Ti in as-cast and T6 heat treated conditions. As revealed through metallographic examinations, fracturing and re-orientation of the second phase particles increased with increasing compression strain. For both conditions of the alloy, the intermetallic particles experienced substantially more frequent cracking than the eutectic silicon. At the same time, the precipitates in the T6 heat treated alloy were also more resistant to rotate within the alloy matrix as a result of nano-size Al3X (X=Zr, Ti, & V) secondary precipitates. The crystallographic texture was measured and correlated with deformation behavior of the alloy. The weak texture of {011} and {111} , {112} and {111} components. The intensity of the components differed depending on the strain amount and the state of precipitation where the T6 heat treated alloy always exhibited lower intensity all over the strain. It is concluded that the texture formation in studied alloy is controlled by precipitates formed during T6 heat treatment.

Dynamic Behavior of Fibre Reinforced Sand

Fibre reinforcement has more or less established itself as a composite civil engineering material having significant effect in improving the static strength characteristics of granular soil like sand. However the dynamic behavior of fibre reinforced sand as far as large scale model tests are concerned is rarely discussed in the literature. The present study illustrates the effect of randomly distributed polypropylene fibrillated fibre reinforcement in modifying the dynamic characteristics of locally available sand (Solani River, Roorkee, India). Block resonance tests (BRT) for low-medium strain levels and Cyclic plate load tests (CPLT) for high strain level have been conducted both on un-reinforced and fiber reinforced sand in the laboratory to study its dynamic characteristics. In BRT, the magnitude of resonant frequency and maximum amplitude of vibration of the test block have been recorded at different excitation levels in vertical mode of vibration at a particular percentage of fiber content, thus establishing the effect of dynamic loading or in turn the effect of strain level. The dynamic response was evaluated in terms of coefficient of elastic uniform compression and damping ratio. Where as, in CPLT, settlement and pressure values have been recorded to calculate coefficient of elastic uniform compression at two different strain levels. It was observed that there was no significant effect of fibre reinforcement on the dynamic behavior of sand contrary to the static loading condition.

웨이블릿 해석을 이용한 콘크리트의 동탄성계수 추정 및 응용

The dynamic modulus of elasticity of concrete can be determined nondestructively using impact echo test as prescribed in KS F 2437. The fundamental longitudinal frequency of the concrete cylinders with free-free boundary condition was estimated by the wavelet transform theory. The advantage of the wavelet transform over either a pure spectral or temporal decomposition of the signal is that the features of the pertinent signals can be characterized in the time-frequency plane. For the concrete mix design utilized in this study, no significant difference between the dynamic and the static moduli of elasticity was observed. This was contrary to the perceived general notion of having the dynamic modulus considerably higher than the static modulus. It has been shown that the modulus from static and dynamic by impact echo test are comparable to each other fairly well, when the effect of strain level was properly taken into account. In this experimental test, it was shown that the dynamic modulus is approximately equal to the tangent modulus at strain level.

Viscoelasticity and Preconditioning of Rat Skin Under Uniaxial Stretch: Microstructural Constitutive Characterization

In spite of impressive progress in developing general constitutive laws for soft tissues, there exists still no comprehensive model valid for any general deformation scheme. The present study focuses on the uniaxial response of the skin as a model for other multifibrous soft tissues. While the skin's nonlinear viscoelastic constitutive response has been extensively studied and modeled, the phenomena associated with mechanical preconditioning have so far not been dealt with. Yet preconditioning is an inherent response feature in the skin, both in vitro and in vivo. It is hypothesized that by considering the structure of the elastic and collagen fibers and their individual rheological properties, it is possible to develop a reliable general constitutive law for the skin's uniaxial response. A stochastic hybrid constitutive model was developed based on the collagen and elastic fiber morphologies and their rheological properties. The multiple protocol uniaxial data of Eshel and Lanir ("Effects of Strain Level and Proteoglycan Depletion on Preconditioning and Viscoelastic Responses of Rat Dorsal Skin," 2001, Ann. Biomed. Eng., 29, pp. 164-172) served to estimate the model's parameters and to validate its reliability. Parametric investigation was then used to test model parsimony (minimal form) and to elucidate the roles of response mechanism and the relative contribution of each constituent. The model predictions show a very close fit to the data and good predictive capability. The results are consistent with the quasilinear viscoelastic response of both elastic and collagen fibers and are likewise consistent with the notion (supported by published experimental observations) that preconditioning in collagen is probably due to an increase in the fiber reference length and is due to strain softening (Mullins effect) in elastic fibers. The predictions also agree with the observed predominance of elastic fibers at low strains and suggest that as strain increases, collagen becomes predominant, but the effect of elastic fibers is still significant. The parsimony analysis of the 22 model parameters (18 are nonlinear in the model) points to the predominant role of viscoelasticity and preconditioning in both fibers, followed in order of importance by collagen waviness and elastic fiber nonlinearity. A reliable and comprehensive uniaxial constitutive law for the rat skin was developed based on the tissue microstructure and on its constituents' rheological properties.

Stress‐relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural rubber‐graft‐polystyrene blends

AbstractWe studied the stress‐relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress‐relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two‐stage mechanism. On the other hand, the cocontinuos morphology showed a single‐stage mechanism. The addition of a compatibilizer (NR‐g‐PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two‐step relaxation mechanism was found in the compatibilized blends. A three‐stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two‐stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The stored energy of cold work: Predictions from discrete dislocation plasticity

The stored energy of cold work is calculated for planar single crystals under tensile loading with plastic deformation occurring through dislocation glide. Superposition is used to represent the solution of boundary value problems in terms of the singular fields for discrete dislocations and image fields that enforce boundary conditions. Constitutive rules are used which account for the effects of line tension and three-dimensional dislocation interactions including dynamic junction formation. The stored energy is calculated both under load and after load removal and methods are devised to estimate the local plastic dissipation and to separate out the contribution of long-range stresses to the energy stored. Calculations are carried out up to imposed strains of 0.05–0.1 and the effects of strain level, dislocation structure and crystal orientation on the evolution of the stored energy are investigated. Although the flow stress and work hardening rate depend mainly on the dislocation density, the stored energy of cold work depends on details of the dislocation structure that forms, with any long-range dislocation stress field playing a significant role. The calculations exhibit a connection between the stored energy of cold work and the Bauschinger effect. It is also found that local energy storage values can differ substantially from the average value.

Post-yield compressed semicrystalline poly(butylene terephthalate): energy storage and release

Post yield deformation of semicrystalline poly(butylene terephthalate) (PBT) is studied by differential scanning calorimetry (DSC) measurements on compressed specimens after unloading. In particular, the effects of strain level, loading-unloading rate, and deformation temperature are analyzed. DSC traces indicate that a remarkable fraction of the mechanical work of deformation (in the range from 25 up to 62%) is stored in the material after unloading. Final strain dependence of stored energy values for specimens deformed up to 40% follows the general S-shaped trend observed for many amorphous and semicrystalline polymers. The ratio of the stored energy to the mechanical work of deformation (Δ U ST/ W) is decreasing as the final deformation level increases. For a given final strain level, the amount of energy stored in specimens deformed under T g increases as either loading or unloading rates increase: in particular, both Δ U ST and Δ U ST/ W values are linearly increasing with the logarithm of loading rate. On the other hand, energy storage for specimens deformed at T g results to be practically independent from the loading rate. Moreover, as the deformation temperature increases from 25 to 100 °C, Δ U ST values markedly decrease, while the ratio Δ U ST/ W is almost constant around an average value of about 51%.

Effects of strain level and proteoglycan depletion on preconditioning and viscoelastic responses of rat dorsal skin.

The mechanical response of rat dorsal skin was experimentally studied under cyclic uniaxial ramp stretches to various strain levels. Special emphasis was paid to the effects of the preconditioning protocol on the stress-strain relationship, and to the effects of ramp strain level and proteoglycan (PG) depletion, on viscoelasticity and preconditioning responses. The results show that preconditioning significantly reduced both the slope of the low strain stress-strain relationship, and the stress levels at consecutive stretch cycles. Following a short rest there was a significant partial recovery. Stress decay due to preconditioning was significant at all strain levels, and increased with strain. Stress relaxation was significant at all strain levels, but varied little with strain. Recovery following a 10 min rest was minor at all strain levels and varied little with strain. PG-depleted samples manifested similar response patterns. These results are consistent with the following notion: (1) skin consists of three mechanical components: elastin and proteoglycan which dominate the low strain response and are effected by preconditioning and (PG) depletion, and collagen which dominates the high strain response and is unaffected by preconditioning and PG depletion; (2) that the viscoelasticity of elastin and PG vs that of collagen are similar, so that rat dorsal skin can be regarded quasilinear viscoelastic.

Stress Relaxation Behavior of Short Pineapple Fiber Reinforced Polyethylene Composites

Stress relaxation behavior of short pineapple fiber reinforced polyethylene composites in tension has been studied with special reference to the effect of fiber loading, fiber length, chemical treatment and fiber orientation. Chemical treatments of fiber with reagents such as isocyanate, silane, alkali and peroxide were carried out to improve the interface adhesion between fiber and matrix. The effects of strain level, chemical treatments, pre-straining, and aging on the rate of relaxation have been investigated. It was found that the stress relaxation rate decreases with strain level. It was found that incorporation of fiber results in two relaxation processes. The rate of relaxation is decreased with fiber content. It is observed that chemical treatment has significant influence on the relaxation behavior. Composites containing fibers oriented longitudinally have higher relaxation rate than transversely oriented composites. Aging of samples improved the relaxation modulus due to improved interfacial adhesion at higher temperature. It has been demonstrated that the stress relaxation modulus values measured at different strains can be superimposed by a shift along the logarithmic time axis to yield master curves of modulus over an extended time period.

A viscoelastic constitutive model for particulate composites with growing damage

A mechanical model which describes time-and temperature-dependent deformation behavior of particulate composites with changing microstructure, including growing damage, is described and then verified by experimental study of a viscoelastic filled elastomer. An existing constitutive model, which is based upon thermodynamics of irreversible processes with internal state variables, is first reviewed and then used to describe the mechanical behavior of elastic and viscoelastic media with changing microstructure. A rate-type equation is successfully employed in describing the evolution of microstructural changes, which are believed here to be primarily microcracking. An elastic-viscoelastic correspondence principle and the time-temperature superposition principle are used in modeling effects of the material's intrinsic viscoelasticity and the effects of temperature changes. Laboratory tests of the stress and dilatation responses of uniaxial test specimens under controlled monotonically increasing axial extension and constant confining pressure at different temperatures were performed. The effects of strain level, strain rate, confining pressure, and temperature on the stress and dilatation are described and compared to the theoretical model.

Stress relaxation in short jute fiber-reinforced nitrile rubber composites

Stress relaxation measurements in tension have been made on nitrile rubber vulcanizates containing short jute fibers. The effects of strain level, bonding system (silica-resorcinol-hexa), fiber orientation, fiber content, temperature, and prestraining on the rate of stress relaxation have been investigated. Existence of a relaxation mechanism within the first 200 s is reported.

Dynamic Property and Fatigue Crack Propagation Research on Tire Sidewall and Model Compounds

Abstract Research was conducted to define appropriate compound loading conditions and energy parameters required to properly control and analyze fatigue crack propagation experiments for tire sidewall applications. The effects of strain level, pulse frequency, overall cycle frequency, sample thickness, and oven temperature were screened, and strain level was shown to be the dominant variable in the region of interest. Designed experiments further confirmed that frequency (i.e., strain rate) effects upon strain energy are small at normal rates of tire deformation (equivalent to 40 Hz). However, at typical laboratory test frequencies (≤5 Hz), strain rate effects on strain energy are large, and the differences vs. results under tire conditions depend heavily on polymer type as well as test temperature. Thus, the use of strain level, strain rate, and temperature conditions which simulate the tire service environment are critical to give representative results in laboratory testing. A constitutive equation was defined which provides an excellent model for strain energy in pure (or simple) shear as a function of the principal extension ratio (i.e., strain level) at constant frequency. Therefore, computer modeling of such experiments appears straightforward using an on-line minicomputer. Fatigue crack propagation studies showed major effects of pure-shear sample thickness, processing prior to molding, different types of reference compounds, and different polymer types. Halobutyl compounds and halobutyl/EPDM/NR blends were shown to provide superior FCP resistance at a given strain or strain energy level. These results were consistent with earlier tire and laboratory data.

Rheo-Optical Studies of Drawn Polyethylene Films

Previous studies of the rheo-optical properties of polyolefins have shown that the rheo-optical properties of undrawn polyolefins can be well explained by considering three deformation mechanisms. When spherulites in polyolefins are broken either partially or completely, drastic changes in the crystalline structure, and hence in the rheo-optical properties, should occur. In order to make this point clear experimentally, birefringence relaxation and stress relaxation were measured simultaneously for low density polyethylene films drawn to various extents.For undrawn and weakly drawn films, the strain—optical coefficient increased with increasing time, while for a highly drawn film, it decreased with increasing time. This indicates that the highly drawn films do not exhibit the mechanism of crystalline orientation, which causes the birefringence to increase with time.The time curves for the strain-optical coefficient and the relaxation modulus obtained at various temperatures could be superposed by vertical and horizontal shifts. Then, from the horizontal shift factors, activation energies for the rheo-optical and viscoelastic relaxation processes were determined. The activation energies for the highly drawn films are much higher than those for the undrawn and weakly drawn films, suggesting the existence of a fourth deformation mechanism.Relaxation experiments were also carried out for undrawn low density polyethylene at different strain levels ranging from 3% to 12% The effect of strain level appears to be equivalent to the effect of drawing in the sense that the peak of the relaxation spectrum at the shorter relaxation times decreases with increasing strain.