Prestrain Values Research Articles

Molecular Dynamics Simulation of Bauschinger Effect in Cu Nanowire with Different Crystallographic Orientation

In this study, the Bauschringer Effect (BE) resulting from tension-compression deformation applied to nanowires obtained by placing Cu atoms in , and highly symmetric crystallographic directions was investigated using the Molecular Dynamics (MD) simulation method. The forces between atoms were determined from the gradient of the Embedded Atom Method (EAM) potential function, which includes many-body interactions. It was determined that there is an asymmetry between the stress-strain curves obtained as a result of the tension and compression deformation process applied to the model system. From this asymmetry, it was determined that the yield stress obtained in the drawing process for nanowire with crystallographic orientation was greater than the yield strain obtained as a result of the compression process. In contrast, the opposite was found for nanowires with crystallographic orientation and . In addition, after the yield strain value is exceeded as a result of the drawing process applied to the model nanowire system, compression deformation process was applied at different pre-strain values. The existence of the Bauschinger Effect (BE), which is expressed as the yield strength value as a result of forward loading corresponding to the tension operation, is smaller than the yield value obtained as a result of the compression process in which the loading is removed, was determined. To clarify the effect of BE on Cu nanowires with different crystallographic orientations, Bauschinger Stress parameter (BSP) and Bauschinger Parameter (BP) values were calculated.

Crossover from mechanical stabilization of martensite to spanning avalanche-type reverse transformation of deformed Cu-Al-Ni shape memory crystals

A new interpretation of factors controlling the kinetics of reverse transformation of martensites stabilized by prestrain is suggested. We investigate the effect of amount of prestrain in the β1´martensite and in the β-phase on temperature and kinetics of the reverse martensitic transformation in Cu-Al-Ni shape memory alloy single crystals. Calorimetry and video recording of the jumping samples, provoked by the burst strain recovery during temperature-induced reverse transformation, are used in experiments. For crystals deformed both in the β´1 martensite and in the β-phase, we report the existence of a sharp transition (crossover) from the mechanical stabilization of martensite to the burst reverse martensitic transformation which proceeds as a single avalanche. The crossover occurs for prestrain values close to the maximum transformation strain. The specific energy of the jump during burst strain recovery depends on the maximum stress applied during prestraining the sample. The crossover from a broad transformation range to an infinite or spanning avalanche is predicted by 3D random field Ising model for disordered systems undergoing the first order phase transition. Based on this model, we explain the crossover in deformed Cu-Al-Ni crystals by a rapid decrease of structural disorder towards the critical one at the final stage of the formation of detwinned γ´1martensite. A simple solution is obtained for the critical transformation rate which produces jumping of the sample during burst reverse transformation after prestrain.

Forming limit of AZ31B magnesium alloy under in-plane complex biaxial loading paths with cruciform specimens

This paper focused on the forming limit curves (FLC) of the AZ31B magnesium alloy sheet metal under different complex loading paths in-plane. Compared with simple loading paths, the study of forming limit of sheet metal under complex loading paths was more practical. In this study, biaxial tensile test of the cruciform specimen was utilized to acquire the FLC after the cruciform specimen was subjected to uniaxial pre-tensile process along rolling direction, which experimentally characterize the forming limits under different pre-strain values of 1.15%, 2.34%, 4.0%, and 5.4%. Subsequently, based on the constitutive model, Hill48 yield criterion and shear failure criterion, the theoretical FLCs of AZ31B magnesium alloy sheet metal was be calculated. Meanwhile, the normal biaxial tensile tests were also simulated by Abaqus to obtain the limit strains by Finite Element Analysis (FEA). Extracting limit strains from the fracture region in FEA model when the first derivative of the strain difference with respect to time reached the maximum value between the first principal strain of necked element and the first principal strain of the element adjacent to the necked zone. As a result, the experimental FLCs was qualitatively consistent with the result of theoretical model and FEA model. In addition, the FLCs of AZ31B magnesium alloy sheet moved to the upper left of forming limit diagram with the increase of the pre-strain, which indicated that the pre-strain process along the rolling direction could significantly improve the formability of the sheet metal.

Instrumented indentation for determining stress and strain levels of pre-strained DC01 sheets

In classical mechanical testing, determining the stress and strain states of complex shape specimens turns out to be very challenging, especially in the most deformed regions. In the latter case, when not enough material is present, non-destructive testing is needed for determining the corresponding mechanical state. In this study, a novel approach, based on the local quasi-non-destructive instrumented indentation technique (IIT) coupled with the inverse analysis technique (IAT), is used to determine the stress and strain levels of pre-strained DC01 specimens using monotonic and non-monotonic loading paths. Monotonic and cyclic shear tests as well as Marciniak tests, in both plane and equi-biaxial strain states, are used to apply different pre-strain levels. For monotonic loading paths, i.e. monotonic shearing and Marcianiak tests, the applied methodology showed very satisfying results in determining the stress and strain states of the pre-strained specimens, especially for pre-strain values close to the representative indentation strain values. A maximum stress error of less than 15% was obtained in the case of the highest applied pre-strain value (29.04%). The purely isotropic Voce hardening law was adopted for determining the hardening behavior of the studied specimens in both cases: as-received and pre-strained. In the case of cyclic shear, a mixed isotropic-kinematic hardening law is to be used to determine the stress and strain states of the pre-strained specimens. Adopting a mixed isotropic-kinematic Chaboche hardening law led to satisfying results where the estimation errors of the applied pre-strain value and corresponding yield stress didn't exceed 6% and 1.3%, respectively. The obtained results show that the proposed indentation-based method can be very useful in estimating the work-hardening level and corresponding plastic deformation of pre-strained parts under various loading paths

Arbitrary Prestrain Values for Ligaments Cause Numerical Issues in a Multibody Model of an Ankle Joint

Experimental studies report that ligaments of the ankle joint are prestrained. The prestrain is an important aspect of modern biomechanical analysis, which can be included in the models by: applying symmetrical, arbitrary prestrains to the ligaments, assuming a strain-free location for the joint or by using experimental prestrain data. The aim of the study was to comparatively analyze these approaches. In total, 4 prestraining methods were considered. In order to do so, a symmetrical model of the ankle with six nonlinear cables and two sphere–sphere contact pairs was assumed. The model was solved in statics under moment loads up to 5 Nm. The obtained results showed that the arbitrary prestrains caused an unbalanced load for the model at rest, and in turn modified its rest location in an unpredictable way. Due to the imbalance, it was impossible to enforce the assumed prestrains and thus cartilage prestrain was required to stabilize the model. The prestraining had a significant effect on the angular displacements and the load state of the model. The findings suggest that the prestrain values are patient specific and arbitrary prestrains will not be valid for most models.

Prestrain in the rabbit eardrum measured by digital image correlation and micro-incisions

Prestrain in the absence of external loads can have an important effect on the vibrational behavior of mechanical systems such as the middle ear. Studies that measure tympanic membrane (TM) prestrain are scarce, however, and provide no conclusive answer on the existence and nature of the prestrain. In this study, prestrain is measured in the TM of cadaveric rabbit ears by stereo digital image correlation. To release the prestrain, straight incisions of 0.33 mm are made on different locations in the TM with a direction parallel to either the radial or circular fibers in the membrane. The effect of sample dehydration during different stages in the experimental procedure is assessed and eliminated by rehydrating the samples directly before each measurement. The measurements demonstrate average prestrain values around the incisions between 3.52±2.34% and 13.62±7.92% for the different locations, with a noise floor of 0.07%. No clear differences were found between the prestrain values obtained for radial and circular incisions. Observed local variations in TM prestrain could not be clearly related to specific locations on the TM. The results suggest that TM prestrain may need to be considered in future studies of middle-ear function if the findings can be confirmed in human ears.

Reverse Analysis of Surface Strain in Elasto-Plastic Materials by Nanoindentation

In this study, nanoindentation technology is utilized to investigate the in situ mechanical behavior of small-sized packaging materials. Rather than the ideal cases with unprestressed materials which have been intensively studies, this paper focuses on the effect of surface stress by prestressing the materials to be indented by a Berkovich indenter. The loading process until the maximum penetration depth is simulated by finite element (FE) models. With elastoplastic materials as described by a power-law model, extensive FE predictions are performed with the wide ranges of Young’s modulus, yield strength and hardening exponent with and without pre-strain. FE results show that with different prestress values, the applied load-penetration depth responses vary in a highly consistent manner. The residual indentation profiles are found to be closely related with the stress state due to the pre-strain values. On the basis of FE simulations, a dimensionless function is therefore derived and a reverse algorithm is proposed to estimate the constitutive parameters and also the surface stress of elastoplastic materials. With one of the most commercialized lead-free solder materials in electronic packaging structures, the proposed reverse algorithm is utilized to estimate the residual stress based on the nanoindentation response of solder samples with different annealing conditions.

WraptMor: Confirmation of an Approach to Estimate Ligament Fiber Length and Reactions With Knee-Specific Morphology.

Knee ligament length can be used to infer ligament recruitment during functional activities and subject-specific morphology affects the interplay between ligament recruitment and joint motion. This study presents an approach that estimated ligament fiber insertion-to-insertion lengths with wrapping around subject-specific osseous morphology (WraptMor). This represents an advancement over previous work that utilized surrogate geometry to approximate ligament interaction with bone surfaces. Additionally, the reactions each ligament imparted onto bones were calculated by assigning a force-length relationship (kinetic WraptMor model), which assumed that the insertion-to-insertion lengths were independent of the assigned properties. Confirmation of the approach included comparing WraptMor predicted insertion-to-insertion length and reactions with an equivalent displacement-controlled explicit finite element model. Both models evaluated 10 ligament bundles at 16 different joint positions, which were repeated for five different ligament prestrain values for a total of 80 simulations per bundle. The WraptMor and kinetic WraptMor models yielded length and reaction predictions that were similar to the equivalent finite element model. With a few exceptions, predicted ligament lengths and reactions agreed to within 0.1 mm and 2.0 N, respectively, across all tested joint positions and prestrain values. The primary source of discrepancy between the models appeared to be caused by artifacts in the finite element model. The result is a relatively efficient approach to estimate ligament lengths and reactions that include wrapping around knee-specific bone surfaces.

The effect of pre-strain and number of SMA wires on the compression properties of glass-epoxy conical grid composites

In the present work, the effect of pre-strain and number of shape memory alloys on the compressive performance of glass/epoxy composite conical shells were studied. The filament-winding process was applied to manufacture the composite specimens, without and with 1 and 2 SMA wires of 0, 1, 2 and 4% pre-strain. Based on the results of the axial compression tests, the maximum stiffness was obtained in the specimen with no SMA wires. Besides, the specimen with 1 SMA wire and 4% pre-strain exhibited the highest level of the compressive load-bearing capacity, which is attributed to the transformation of austenite to twinned martensite (shape memory effect) due to the higher value of pre-strain. Finally, scanning electron microscopy was conducted, and it was found to be consistent with the results of the compression tests on the specimens.

Self-heating of metastable 304L austenitic stainless steel under cyclic loading: Influence of initial martensite volume fraction, testing temperature and pre-strain

In this study, special attention is paid to the thermal response of the austenitic stainless steel 304L under cyclic loading tests (i.e., self-heating tests) in different conditions. The cyclic behavior of the 304L austenitic stainless steel can be influenced by martensitic transformation. Hence, the role of martensitic transformation in the self-heating behavior of this material is studied. For this purpose, self-heating tests are performed on pre-strained specimens at a wide range of temperatures from 100 °C to −130 °C, which leads to different initial volume fractions of martensite ranging from 0% to 45%, respectively. Furthermore, the influence of the testing temperature and a pre-strain at room temperature on the self-heating curves is investigated. The results demonstrate that the decrease in the test temperature from room temperature to - 30 °C as well as the increase in the pre-strain values from 0% to 30% at room temperature, result in a shift of the self-heating curves to the right. It could mean that the fatigue limit of the material is improved.

Bistable structures with controllable wrinkled surface

The deformation of a tri-layer composite rubber from a mono-stable saddle, a monostable state with wrinkles, a bistable cylinder, to a bistable state with wrinkles was investigated in this work. Among these forms, the wrinkled bi-stability was a unique shape that combined two different deformations into one structure and was primarily studied. The dependence of the rubber shape on the geometric and mechanical parameters was investigated. The phase diagram for the rubber transformation provides accurate pre-strain values and width of structure that correspond to various states. Finite element analysis could reproduce these deformation states well considering the above influencing factors. For the bistable surface, the inner layer was wrinkled, while the outer layer remained flat at the same pre-strain. The morphological differences could be related to the constraints in a manner that is analogous to unidirectional strain. Furthermore, the pre-strain field of the top and bottom layers could be simplified to one layer using Poisson’s ratio. The investigated deformation processes have potential applications for the precise control of flexible machines and robots.

Hydrogen embrittlement sensitivity of X100 pipeline steel under different pre-strain

In the present study, the influences of hydrogen on the mechanical properties as well as the pre-strain on the HE susceptibility of X100 pipeline steel were investigated by combining electrochemical hydrogen charging and tensile experiments. Both the yield and tensile strength decrease with the increasing hydrogen charging time no matter the values of pre-strain. When the charging time is 12 h, the yield strength and tensile strength was reduced by 3% and 9%, respectively. The longer the charging time, the stronger the HE damage of the steel. Besides, when the hydrogen charging time is same, HE sensitivity increases with the pre-strain values. When the charging time is 6 h, the HE sensitivity coefficient is 40.24% without pre-strain, and it increases to 49.26% with the pre-strain value increases to the 2%. The hydrogen effective diffusion coefficient reduces gradually with the increasing pre-strain values. The coefficient is 5.45 × 10−7 cm2/s without pre-strain and it reduces to 1.21 × 10−7 cm2/s with the pre-strain value increases to the 3%. When the hydrogen charging time is same, HE sensitivity increases with the pre-strain values.

Tunable wave propagation by varying prestrain in tensegrity-based periodic media

This paper investigates the dynamic properties of one, two and three-dimensional tensegrity-based periodic structures introduced in Rimoli and Pal (2017), which are here termed as tensegrity beams, plates and solids, respectively. We study their linear wave propagation properties and show that in each case, these properties can be significantly altered by the prestrain in the cables. As the prestrain is varied, we observe jumps in the wave velocities at two critical prestrain values, which define transitions between the three distinct phases of these structural assemblies. At low cable prestrains, the wave speeds are zero as the lattices have zero effective stiffness. At moderate prestrains, the wave speed is nonzero and finally, at prestrain levels where the bars buckle, the wave speeds change to a near constant value. Dispersion analysis on these beams, plates and solids reveal unique properties such as very low wave velocities compared to their constituent material and the existence of flat bands at low frequencies. Furthermore, we find that shear waves travel faster than longitudinal waves in tensegrity solids in a range of cable prestrains. Finally, we verify the key observations through detailed numerical simulations on finite tensegrity solids.

Non-linear load-deflection response of SMA composite plate resting on winkler-pasternak type elastic foundation under various mechanical and thermal loading

This study investigates the non-linear load-deflection behavior of a composite plate reinforced with Shape Memory Alloy (SMA) fibers. The plate is subjected to the uniform lateral pressure and thermo-mechanical loading while resting on a Winkler-Pasternak type elastic foundation. In SMA fibers, simple one-dimensional Brinson’s model is implemented to determine tensile recovery stresses due to the phase transformation. The non-linear semi-analytical solution is formulated for the examination of the large deflections including the preliminary geometrical imperfection. The governing equations of equilibrium are derived in terms of displacement and stress function. The Galerkin technique is chosen to solve the nonlinear partial differential equations of motions. A detailed parametric study including different SMA material properties, SMA fiber pre-strain values, SMA fiber volume fraction, foundation stiffness, and activation temperature are examined.

Numerical simulation of prestrain history effect on ductile crack growth in mismatched welded joints

AbstractPipe reeling may lead to plastic pre‐deformation (prestrain) around existing cracks in components; therefore, investigating whether this process accelerates or counteracts ductile crack growth, especially for strength mismatched welded joints, is warranted. This study focused on the effect of prestrain history on ductile crack growth in mismatched welded joints. A single‐edge‐notched tension specimen was selected for numerical study, and the crack was assumed to have existed before a prestrain history was applied. Crack growth resistance curves for plane strain and mode I crack growth under large‐scale yielding conditions have been computed using the complete Gurson model. Meanwhile, symmetrical and non‐symmetrical prestrain cycle modes with different loading levels were applied to the overmatched specimens. The outcome demonstrated that the mismatch ratio (the ratio between the yield stress of the weld metal and base metal) showed a significant effect on fracture resistance regardless of the stage at which the prestrain cycle loading was located. By contrast, the processing of the crack growth was weakened by the increase of prestrain values, and the symmetrical prestrain cycle resulted in greater plastic damage than the non‐symmetrical prestrain cycle did. However, the initial crack length had a non‐significant effect on the ductile fracture considering the prestrain and mismatch effects.

Tensile and compressive behaviors of prestrained single-layer black phosphorus: a molecular dynamics study.

The effect of prestrain on tensile and compressive behaviors of single-layer black phosphorus (SLBP) in both armchair and zigzag directions is investigated by using molecular dynamics simulations. Prestrain is carried out by stretching or compressing SLBP in an orthogonal in-plane direction. The results show that the overall mechanical properties of SLBP, including Young's modulus, tensile strength, compressive strength, and yield strength are enhanced with an increase in compressive prestrain but are reduced with an increased tensile prestrain. With the same value of prestrain, SLBP exhibits unidirectional-homogeneous characteristics for tensile and compressive deformation. It is demonstrated that the armchair-oriented prestrain leads to a more significant improvement in the overall mechanical properties than the zigzag-oriented prestrain, indicating the anisotropic deformation behavior due to the characteristic puckers in SLBP. This work also reveals the mechanisms of prestrain underlying the mechanical behaviors of SLBP at the nanoscale, suggesting that the application of prestrain is an effective way to modify the mechanical properties of two-dimensional materials.

Effect of ferrite-martensite interface morphology on bake hardening response of DP590 steel

The effect of martensite spatial distribution and its interface morphology on the bake hardening characteristics of a dual phase steel was investigated. In one case, typical industrial continuous annealing line parameters were employed to anneal a 67% cold rolled steel to obtain a dual phase microstructure. In the other case, a modified annealing process with changed initial heating rates and peak annealing temperature was employed. The processed specimens were further tensile pre-strained within 1–5% strain range followed by a bake hardening treatment at 170°C for 20min. It was observed that industrial continuous annealing line processed specimen showed a peak of about 70MPa in bake-hardening index at 2% pre-strain level. At higher pre-strain values a gradual drop in bake-hardening index was observed. On the contrary, modified annealing process showed near uniform bake-hardening response at all pre-strain levels and a decrease could be noted only above 4% pre-strain. The evolving microstructure at each stage of annealing process and after bake-hardening treatment was studied using field emission scanning electron microscope. The microstructure analysis distinctly revealed differences in martensite spatial distribution and interface morphologies between each annealing processes employed. The modified process showed predominant formation of martensite within the ferrite grains with serrated lath martensite interfaces. This nature of the martensite was considered responsible for the observed improvement in the bake-hardening response. Furthermore, along with improved bake-hardening response negligible loss in tensile ductility was also noted. This behaviour was correlated with delayed micro-crack initiation at martensite interface due to serrated nature.

Effect of normal compression on the shear modulus of soft tissue in rheological measurements

While the effect of normal compression on the measured shear material properties of viscoelastic solids has been already acknowledged in rheological studies in the literature, to our knowledge, no systematic study has been conducted to investigate this effect in detail to date. In this study, we perform two sets of experiments to investigate the effect of normal strain and strain rate on the dynamic shear moduli of bovine liver. First, we apply normal compressive strain to the cylindrical bovine samples up to 20% at loading rates of v=0.000625, 0.00625, 0.0625, 0.315, 0.625mm/s. Second, we perform torsional shear loading experiments, in the frequency range of ω=0.1–10Hz, under varying amounts of compressive pre-strain (ε=1%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% and 20%) applied at the quasi-static loading rate of v=0.000625mm/s. The results of the experiments show that the shear moduli of bovine liver increase with compressive pre-strain. A hyper-viscoelastic constitutive model is developed and fit to the experimental data to estimate the true shear moduli of bovine liver for zero pre-compression. With respect to this reference value, the mean relative error in the measurement of shear moduli of bovine liver varies between 0.2% and 243.1% for the compressive pre-strain varying from ε=1% to 20%. The dynamic shear modulus of bovine liver for compressive pre-strain values higher than ε>2.5% are found to be statistically different than the true shear moduli estimated for zero compressive strain (p<0.05).

Influence of static strain aging on the cleavage fracture of a C–Mn steel

Recent advances in the constitutive modeling of strain aging effects in elastoviscoplasticity are used to predict the ductile-to-brittle transition curve for a C–Mn steel depending on pre-straining and heat treatment. The parameters of the Beremin model are identified from a large experimental basis of Charpy tests. 3D finite element simulations of Charpy V-notched specimens based on a constitutive model accounting for static strain aging, are performed for the first time to predict the fracture behavior of the pre-strained and aged material. The constitutive model includes the strain localization phenomena occurring in the notch due to Lüders effects. Good agreement between experiment and modeling is demonstrated. The introduction of kinematic hardening improves the prediction of the lower part of the ductile-to-brittle transition region. The proposed approach aims at optimizing pre-strain values and heat treatments for nuclear steels.

Influence of a Tensile Pre-Strain on Bending of Aluminium Alloy

The mechanical behavior of thin sheets of aluminium alloy 6016, of thickness 1.14 mm, was investigated in unconstrained bending, with or without a tensile pre-strain. In the case of bending without pre-strain, no rupture was observed. Therefore, a tensile pre-strain, ranging from 0.19 up to 0.45 (longitudinal strain), was applied prior to bending. The highest pre-strain values were reached within the necking area. Tensile tests on rectangular samples were performed, then reduced samples were cut out and submitted to bending. A Digital Image Correlation (DIC) system was used to measure the maximum local strains reached during both tests. The evolution of the applied load on the bending tool versus its displacement showed that a rupture in bending was obtained for tensile pre-strains higher than 0.25, as evidenced by a load drop. These results showed that very high strains can be reached in bending, which is consistent with previously obtained numerical results.