Stress-strain Plots Research Articles

Mechanical behavior of dissimilar AL6XN-IN718 welded joint obtained by cold metal transfer

Cold metal transfer (CMT) welding process was used to join the AL6XN super-austenitic stainless steel to a nickel-based super alloy IN718. Microhardness, tensile and low cycle fatigue tests were carried out to determine the mechanical properties of the welded joint. The heat used to perform the weld decreases the microhardness in the heat affected zone (HAZ) of the IN718 material. A decrement of about 50% with respect to the base material (∼410 HV0.2) was observed, which is attributed to the microstructural transformation produced by the weld thermal cycles, inducing the partial dissolution of the γ'′ phase in the nickel matrix. In contrast, the HAZ on the AL6XN side, the microhardness tends to be similar with respect to the base material (∼203 HV0.2). In terms of the fracture energy, determined from the stress-strain plot, the welded joint decreases about 60–65% with respect to the base materials. This tendency was also observed in the case of the Charpy impact test behavior. From the low cycle fatigue test, it was observed that AL6XN material and AL6XN-IN718, performed better than the IN718 alloy, i.e. more tolerance to the strain cyclic, increasing the number of cycles to failure. A 3-D transient thermal conduction finite element model was developed to correlate the thermal history with the microstructural transformation on the HAZ and mechanical properties. The weld thermal cycles are in good agreement with the experimental measurements obtained by K-type thermocouples.

Influence of Complex Geometries on Damage Tolerance of Porous Carbon Fiber Network

Porous materials exhibit a variety of attractive functional properties for aerospace applications, such as low density and low thermal conductivity. However, they must also be mechanically robust and damage tolerant to fully realize their potential. Currently, it is costly and time-consuming for testing under service conditions, therefore, computational models are a good path forward. Due to the inherent microstructural stochasticity of these structures, however, their behavior is difficult to effectively model without detailed experimental studies for validation and benchmarking. To that end this study investigates the mechanical properties of a porous carbon fiber network and ties together the global macroscopic observations to the local mesoscale behaviors dictated by individual fibers and fiber junctions. Strain localization was observed using digital image correlation (DIC) and tied to features within the macroscopic stress–strain plots. Work to quantify the impact of the addition of complex geometries (e.g., cracks and through-holes) on mechanical reliability was conducted. The defects resulted in distinct macroscale mechanical characteristics and mesoscale deformation behaviors, depending on defect type and loading orientation. These results provide broad experimental data to inform and validate modeling approaches to accurately predict and tailor the reliability of porous parts under service conditions.

Development and biomechanical testing of full-scale human brain simulant

In 21st century, traumatic Brain Injuries (TBI) due to blast exposure or head impacts in contact sports, accidents are one of most critical research area. But the area of TBI is poorly investigated due to the limitation of brain tissue availability and related ethical/biosafety issues. In general, the brain tissue is difficult to acquire after the autopsy and test in laboratorial settings. In this work, a full-size human brain simulant was developed using a biofidelic multi-part polymeric material poured into a negative mould which was designed and 3D printed. Based on the number of mild to moderate traumatic brain injury cases reported in the literature, three TBI prominent locations were chosen. The prefrontal cortex of frontal lobe, top portion of parietal lobe and temporal lobe of right hemisphere of the brain were the locations where the experiments were conducted under compressive loading conditions. The load versus displacement data was recorded and converted to the stress-strain plots to analyse the result responses and its implications. Two constitutive hyperelastic models (Yeoh model and Neo-Hookean) were selected for curve fitting and characterizing the non-linear mechanical behavior of the full-scale brain model. Such precisely developed and characterized full-scale brain simulant has not been reported in the literature to date and would be beneficial for simulating a wide range of traumatic brain injuries and surgical training.

Investigation of failure behavior of glass fiber reinforced epoxy laminate under fatigue loading

Purpose This study aims to evaluate the failure behavior of glass fiber-reinforced epoxy (GFRE) laminate subjected to cyclic loading conditions. It involves experimental investigation and statistical analysis using Weibull distribution to characterize the failure behavior of the GFRE composite laminate. Design/methodology/approach Fatigue tests were conducted using a tension–tension loading scheme at a frequency of 2 Hz and a loading ratio (R) of 0.1. The tests were performed at five different stress levels, corresponding to 50%–90% of the ultimate tensile strength (UTS). Failure behavior was assessed through cyclic stress-strain hysteresis plots, dynamic modulus behavior and scanning electron microscopy (SEM) analysis of fracture surfaces. Findings The study identified common modes of failure, including fiber pullouts, fiber breakage and matrix cracking. At low stress levels, fiber breakage, matrix cracking and fiber pullouts occurred due to high shear stresses at the fiber–matrix interface. Conversely, at high stress levels, fiber breakage and matrix cracking predominated. Higher stress levels led to larger stress-strain hysteresis loops, indicating increased energy dissipation during cyclic loading. High stress levels were associated with a more significant decrease in stiffness over time, implying a shorter fatigue life, while lower stress levels resulted in a gradual decline in stiffness, leading to extended fatigue life. Originality/value This study makes a valuable contribution to understanding fatigue behavior under tension–tension loading conditions, coupled with an in-depth analysis of the failure mechanism in GFRE composite laminate at different stress levels. The fatigue behavior is scrutinized through stress-strain hysteresis plots and dynamic modulus versus normalized cycles plots. Furthermore, the characterization of the failure mechanism is enhanced by using SEM imaging of fractured specimens. The Weibull distribution approach is used to obtain a reliable estimate of fatigue life.

Bending and twisting behavior of multilayer graphene

In this work, multilayer graphene was chosen and modeled in ANSYS software. In the software, it was subjected to bending forces through various bend angles. In order to test for bending, the model is subjected to rigid support on the base side. Then a force is applied on the side on which the angle is provided to simulate Bending. Stress–strain plots were analyzed for various bending angles. The graphene sheet was also subjected to twist forces within the software. In order to test for torsion, the model is subjected to rigid support on both sides. Then a couple is applied on the opposite sides to simulate torsion. Torsional stress and strain measurements were analyzed. The trends were studied and correlations with the material properties of graphene were established. The quest is to identify a magic angle for bend and twist.

Effect of graphene nano-platelets coating on carbon fibers on the hygrothermal ageing driven degradation of carbon-fiber epoxy laminates

While spray coating of graphene nano-platelets (GNPs) on-to long carbon fibers (CF) is a viable strategy to enhance the strength of carbon fiber reinforced plastics (CFRP), the degradation of these laminates under hot and humid conditions remains unexamined. Here, Pristine and 0.4 % GNP coated CF (0.4GNP) laminates are manufactured using vacuum assisted resin transfer molding (VARTM) technique and subjected to hygrothermal ageing in de-ionized water at 75 °C for 30 days. Mechanical and structural characterization are performed after 15 and 30 days of hygrothermal ageing once the specimens were dried long enough to attain a saturation in mass. 0.4GNP laminate offered higher water resistance than Pristine laminate as 0.4 wt% non-functionalized GNP coated CFs were more hydrophobic than Pristine CF as quantified through contact angle-based measurements. Additionally, a thick carbonaceous hydrophobic interphase is formed between the CF and epoxy for 0.4GNP laminate which hinders water transport in composite. The thicker interphase also enhances the tensile strength and interlaminar shear-strength (ILSS) of 0.4GNP laminate in the unaged condition through enhanced CF—epoxy mechanical locking and epoxy strengthening in the vicinity of CF. However, both tensile strength and ILSS decreased with hygrothermal ageing time and the enhancement in strength achieved through GNP addition is completely lost after 15 days of hygrothermal ageing. Under tensile loading, the stress-strain plots showed a step-wise decrement in stress due to a ply-by-ply failure triggered by failure of the weakened inter-ply epoxy regions. In case of ILSS specimens the number of delaminations triggered increased considerably with hygrothermal ageing.

Establishment of a facile technique to fabricate bulk AA6061/CNT composite with improved mechanical properties using combined stir-casting and squeeze-casting

Three dispersion techniques were investigated for fabricating AA6061–0.5 wt% CNT composites by combined stir-casting and squeeze-casting - direct drop of CNT (DD), mixed Al and CNT pellet drop (PD), and direct drop of ultrasonicated CNT (USDD). Al-20Mg alloy was added to enhance CNT wettability. The PD samples resulted in the highest retention of CNTs in the matrix along with a uniform distribution, confirmed by detailed transmission electron microscope analysis. The selected area electron diffraction pattern and X-ray diffraction confirmed the formation of Mg2Si. The hardness of all composite samples increased significantly over AA6061, predominantly due to a reduction in crystallite size and an increase in dislocation density. The best combination of tensile properties was achieved in the PD composite, yielding an improvement of ultimate tensile strength and yield strength by 40% and 33%, respectively, compared to as-cast AA6061 without sacrificing the ductility. Well-developed serrations were observed in the stress-strain plots of the samples, which have been attributed to the pinning-unpinning action of mobile dislocations by the Mg solute atoms. The fracture surface of the PD composite displays features of ductile fracture along with CNT bridging and rupture, confirming the presence of a strong interface and effective load transfer strengthening.

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

A methodology for post-processing the four-point beam bending data and computing stiffness modulus using harmonic analysis

The computation of modulus of bituminous mixes from a beam bending test conforming to an undamaged yet steady state is not straightforward. The most widely used practice of choosing the 50th or 100th cycle, for modulus computation, does not ensure that the material response has reached a steady state, crossing the initial transient stage of drastic modulus reduction. In the current study, it is analytically shown that the material retardation time governs the attainment of a steady state response. The study proposes a methodology for post-processing the four-point beam bending test data so as to identify the cycles that could result in a sensible computation of material modulus. The experimental investigations involve four-point beam bending (4-PB) tests carried out on four bituminous mixes, prepared using an unmodified and three modified binders. The 4-PB tests are carried out at 20 oC, 10 Hz frequency at strain levels of 200, 400, 600 and 800 micro-strains. The harmonics of the input/output waveform has been used to identify the cycles that can be used for the computation of a material modulus, and the modulus is computed from the Lissajous plots (stress–strain plots) of the cycles prior to damage initiation. Based on harmonic analysis, the current study specifies a range of modulus for each mix at various strain levels, and the values are further compared with the modulus computed using the conventional post-processing procedure. It is observed that the conventional procedure of using the stiffness modulus at 100th cycle results in higher values of modulus than the ones computed using the proposed post-processing method, as a consequence of the transient response of the material before attaining a steady state.

Predicting the double-yield phenomenon in low-density polyethylene film using three-network viscoplastic model

Several Semi-Crystalline Polymers (SCPs) exhibit a Double-Yield (DY) phenomenon in the stress vs. strain response when subjected to uniaxial tensile load. There are only few constitutive models that can predict the DY phenomena at different temperatures and strain rates. These models were developed considering no deformation of crystalline phase, when the amorphous phase gets deformed, whereas in reality all the phases deform concurrently. In this investigation, a Three-Network (TN) viscoplastic model was employed to capture the DY phenomenon in the Low-Density Polyethylene (LDPE) films by considering simultaneous deformations in the amorphous and crystalline (lamellar) phases. The TN model comprised of three parallel networks, A, B, and C, with A and B consisting of non-linear springs and dashpots in series with each other and C containing a non-linear spring solely. While network A of the TN model influences the inter-lamellar shear resistance and the first yield point in the engineering stress vs. strain curve, networks B and C operate together to predict the second yield point. Furthermore, network B regulates the resistance to intra-lamellar shear fragmentation and orientation of lamellar phases. Network C accounts for both the rubbery effect of the amorphous phase and the resistance to fibril deformation along the loading direction at higher strains. To retrieve the TN model parameters, uniaxial tensile tests were conducted on the LDPE films at two different strain rates and temperatures ranging from ambient temperature (25 °C) to 110 °C. The engineering stress vs. strain graphs exhibited the DY phenomenon for all temperatures considered. Stress vs. strain curves were calibrated using the TN model in MCalibration software at certain temperatures (25 °C, 50 °C, 70 °C, and 90 °C) and loading rates (∼10−3/s and 10−2/s). The calibration results corroborated the experimental findings, particularly in terms of capturing the DY phenomenon. Also, simulations using calibrated TN model parameters satisfactorily predicted experimental stress-strain plots at remaining temperatures (40 °C, 60 °C, 80 °C, and 110 °C), demonstrating its versatility in predicting stress and strain characteristics. For the wide range of temperature (25 °C–110 °C) and strain rates considered, an overall difference of ∼5% is observed between the experimental and predicted stress vs. strain data.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

The Ogden model for hydrogels in tissue engineering: Modulus determination with compression to failure

Hydrogel mechanical properties for tissue engineering are often reported in terms of a compressive elastic modulus derived from a linear regression of a typically non-linear stress-strain plot. There is a need for an alternative model to fit the full strain range of tissue engineering hydrogels. Fortunately, the Ogden model provides a shear modulus, μ0, and a nonlinear parameter, α, for routine analysis of compression to failure. Three example hydrogels were tested: (1) pentenoate-modified hyaluronic acid (PHA), (2) dual-crosslinked PHA and polyethylene glycol diacrylate (PHA-PEGDA), and (3) composite PHA-PEGDA hydrogel with cryoground devitalized cartilage (DVC) at 5, 10, and 15%w/v concentration (DVC5, DVC10, and DVC15, respectively). Gene expression analyses suggested that the DVC hydrogels supported chondrogenesis of human bone marrow mesenchymal stem cells to some degree. Both linear regression (5 to 15% strain) and Ogden fits (to failure) were performed. The compressive elastic modulus, E, was over 4-fold higher in the DVC15 group relative to the PHA group (129 kPa). Similarly, the shear modulus, μ0, was over 3-fold higher in the DVC15 group relative to the PHA group (37 kPa). The PHA group exhibited a much higher degree of nonlinearity (α = 10) compared to the DVC15 group (α = 1.4). DVC hydrogels may provide baseline targets of μ0 and α for future cartilage tissue engineering studies. The Ogden model was demonstrated to fit the full strain range with high accuracy (R2 = 0.998 ± 0.001) and to quantify nonlinearity. The current study provides an Ogden model as an attractive alternative to the elastic modulus for tissue engineering constructs.

Experimental and finite element investigations on formability of friction stir welded tailor welded blanks of AA6061 and AA2017

Basically, the use of forming limit diagrams has been increased and dertermined as a recognizing technique for obtaining tailor welded blank's formability. In this present investigation, an effort was made to calculate the formability of friction stir welded (FSW) dissimilar alloys by varying the three main process parameters such as tool rotational speed (TRS), weld speed (WS), and tool tilt angle (TTA). All possible combinations of dissimilar sheets were used for experimental and simulation studies to test the limiting dome height. Material characteristics such as densities, young's modulus, as well as all behaviors of blanks were manually allocated for simulation, using true stress vs true strain plots. The simulation process is performed by considering the whole blanck as three zones with heights of limiting dome seem to be nearer with simulation studies and experimental results. With consideration of Forming limit diagram along with assistance of profiles of strain distribution the formability of all dissimilar blanks was evaluated. Blanks that were tailor welded at a TRS of 13,00 rpm, WS of 20 mm/minute, and tool tilt angle considering 10 exhibited higher formability compared to the blanks friction stir welded at various conditions.

Fourier-transform rheology and printability maps of complex fluids for three-dimensional printing

Direct ink writing (DIW) is a three-dimensional (3D) printing technique exploited by researchers working in fields from scaffolds for energy applications to bioprinting. DIW's main strength is that it enables shaping advanced materials, if these materials can be formulated into complex fluids that meet the demands of the printing process. They must be extremely shear thinning soft solids, able to flow through narrow nozzles, recovering their structure upon deposition and retaining the predesigned 3D shape. Formulation design and rheology are critical, but these aspects can be overlooked due to the high specialization required. This work provides insight on the rheology and printability of complex yield-stress fluids through the study of linear and nonlinear behaviors using large-amplitude oscillatory shear rheology. We refine previous protocols and develop tools to understand the behaviors of formulations for DIW. We apply an existing mathematical framework to a library of carbon-based formulations for energy applications. Fourier transform analysis enables quantifying the onset and rising of higher harmonic contributions. Quantitative comparisons between different formulations are established using 3D harmonics maps, stress–strain plots, and material measures of nonlinearities [Fourier and Chebyshev coefficients, elastic moduli (GM′, GL′), and dimensionless index of nonlinearity (S)]. 3D Lissajous plots provide a qualitative alternative to interpretate the yielding transition. We create Ashby-type printability maps to guide formulation design and elucidate that non-printable formulations show distinctive features. This insight on yield-stress fluids for DIW is relevant to other applications and technologies: drilling fluids, gels, colloids, and foods.

Influence of pin profile on formability of friction stir-welded aluminum tailor-welded blanks: an experimental and finite element simulation analysis

In sheet metal forming processes, the forming limit diagram is frequently employed as a criterion for predicting necking initiation. This is one of the most useful and effective methods for the evaluation of the formability of tailor-welded blanks. The goal of this study was to determine the formability of friction stir-welded (FSW) aluminium alloy 6061-temper 6 (AA6061-T6) and aluminium alloy 2017-temper 6 (AA2017-T6) by employing five dissimilar tool pin profiles. To evaluate the limiting dome height, five different combinations of dissimilar blanks were used in experimental and simulation experiments. Material characteristics such as density, elastic modulus, and all multilinear behaviors of blanks were manually assigned for simulation from the test results of true stress versus true strain plots. The punch with die supports was considered as a rigid body, whereas the metallic blanks were considered as plastic material. To carry out the simulation, the entire blank was divided into three zones. The results obtained from the experimental and simulation results showed that the straight square tool pin profile is the optimal tool pin profile for the formability of FSW AA6061-T6 and AA2017-T6. The tested height values obtained from the limiting dome height were 20.5 and 20.9 mm in experimentation and simulation, respectively. The straight cylindrical tool pin profile exhibited the worst formability properties in both experimentation and simulation.

Oligodendrocyte tethering effect on hyperelastic 3D response of axons in white matter

A novel finite element model is proposed to study the mechanical response of axons embedded in extracellular matrix when subjected to tensile loads under purely non-affine kinematic boundary conditions. Ogden hyperelastic material model describes the axons and the extracellular matrix material characterizations. Two axon-glia tethering scenarios in white matter are studied a single oligodendrocyte (single-OL) with multiple connections a multi-oligodendrocyte (multi-OL) one. In the multi-OL tethering configuration, resultant forces are randomly oriented as distributed glial cells arbitrarily wrap around axons in their immediate vicinity. In the single-OL setup, a centrally located oligodendrocyte myelinates multiple axons nearby. Tethering forces are directed towards this oligodendrocyte, resulting in greater directionality and farther-reaching stress distribution. The oligodendrocyte connections to axons are represented by a spring-dashpot model. The material properties of myelin served as the upper limit for the parameterization of the oligodendrocyte stiffness (“K"). The proposed FE models enable realization of connection mechanisms and their influence on axonal stiffness to determine resultant stress states accurately. Root mean square deviation analysis of stress-strain plots of different connection scenarios reveal an increasing axonal stiffness with increasing tethering, indicating the role of oligodendrocytes in stress redistribution. In single-OL submodel, for the same number of connections per axons, RMSD values increased as “K" (the oligodendrocyte spring stiffness) values were set higher. RMSD calculations reveal that for a “K" value, single-OL model yielded slightly stiffer models compared to multi-OL. The current study also addresses the potential geometrical limitations of multi-OL model by randomizing and adding connections to ensure greater responsiveness. Cyclic bending stresses noticed in both submodels suggest the risk of axonal damage accumulation and repeated load failure.

Synthesis and Characterization of Biocomposite Films of Methylcellulose-Based with Nanocellulose

This study explores the development of nontoxic biocomposite films from methylcellulose (MC) and crystalline nanocellulose (CNC). First, a methylcellulose sample (Tylose MH 50) of concentration 1.5% (w/w) and crystalline nanocellulose type-1 samples of different concentrations were prepared to obtain these biocomposite films. Films were then produced by adjusting methylcellulose solution with nanocellulose solution following the casting-evaporation methodology. The molecular interactions of crystalline nanocellulose with methylcellulose were investigated using ATR Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis of films revealed a shift of absorption peak in the region of 3200-3600 cm-1 to a lower value and found an intense peak at 1031 cm-1 with the incorporation of CNC into Tylose MH 50 film. The thermal stability of these films was examined using thermogravimetric analysis (TGA), indicating the films' higher stability than MC. Mechanical properties were measured by controlled RH by dynamic mechanical analysis (DMA), showing changes in Young's modulus from the initial slope of stress-strain plots and storage modulus (E′) as the concentration of CNC increased in films. The data were obtained from bionanocomposite films, which were not even with variations in thickness as measured by a digital micrometer. The mechanical properties of bionanocomposite films showed variation due to the varying local orientation of CNCs in MC, as it contradicts work that was previously done in this area which suggests a uniform orientation of CNCs in MC biopolymer. Further research on these biocomposite films is expected to find more significant uses.

Unraveling the effects of interface orientation and crystallography on the deformation mechanisms of accumulative roll-bonded Cu-Nb-multilayered nanocomposites using molecular dynamics.

This work elucidates the effect of interface orientation, loading mode, and crystallography on the deformation mechanisms of Cu-Nb-multilayered nanocomposites. Molecular dynamics simulations of deformation behavior of accumulative roll-bonded Cu-Nb-multilayered nanocomposites (MNCs) were performed at room temperature conditions and at a constant strain rate under iso-stress and iso-strain conditions. Interface deformation mechanisms involving nucleation of partial dislocation at the interface and gliding in the Cu layer were observed under iso-stress and iso-strain conditions. Uniaxial stress-strain curves were analyzed for tension and compression under iso-stress and iso-strain loading conditions. The stress-strain plots were explored to understand the elastic, yield, and post-yielding behavior of Cu-Nb MNCs. Under compression with interface orientation normal to the loading direction, twin nucleated via gliding of partial dislocations. Under tension in the iso-stress case, only slip-assisted deformation was observed. Conversely, the deformation behavior under compression and tension was via slip and twinning, respectively, for iso-strain conditions.

Finite element analysis of biodegradable Ti/polyglycolic acid composite bone plates based on 3D printing concept

Dense metallic bone plates often cause stress shielding, delayed healing, or bone non-unions. Therefore, three-dimensional models of partially biodegradable titanium/polyglycolic acid (Ti/PGA) composite cubes with strut thicknesses of 0.33–1.25 mm were designed to achieve different mechanical properties, and compressive simulations of these models were performed to construct stress–strain plots. Finite element models of these plates were assembled with tibial bone fractures using six bicortical screws. Callus volumes were predicted using a rejection coefficient algorithm, and a mechanoregulation algorithm based on deviatoric strain and fluid flow was employed to simulate the healing process. The effective Young’s moduli were 12.13–84.6 GPa during the first week and 4.4–80 GPa during the sixth week, while the callus volume increased after reducing the Young’s modulus of the bone plate. Thus, the additively manufactured design of biodegradable bone plates can be controlled to achieve the appropriate initial Young’s modulus and degradation rate.

In Situ Micro-Observation of Surface Roughness and Fracture Mechanism in Metal Microforming of Thin Copper Sheets with Newly Developed Compact Testing Apparatus.

A better understanding of material deformation behaviours with changes in size is crucial to the design and operation of metal microforming processes. In order to facilitate the investigation of size effects, material deformation behaviours needed to be determined directly from material characterizations. This study was aimed at the design and manufacture of a compact universal testing machine (UTM) compatible with a 3D laser-confocal microscope to observe the deformation behaviour of materials in real-time. In this study, uniaxial micro tensile testing was conducted on three different thin (0.05 mm, 0.1 mm, and 0.3 mm) copper specimens with characteristic dimensions at micro scales. Micro tensile experimental runs were carried out on copper specimens with varying grain sizes on the newly developed apparatus under a 3D laser-confocal microscope. Microscale experiments under 3D laser-confocal microscope provided not only a method to observe the microstructure of materials, but also a novel way to observe the early stages of fracture mechanisms. From real-time examination using the newly developed compact testing apparatus, we discovered that fracture behaviour was mostly brought about by the concave surface formed by free surface roughening. Findings with high stability were discovered while moving with the sample grasped along the drive screw in the graphical plot of a crosshead’s displacement against time. Our results also showed very low mechanical noise (detected during the displacement of the crosshead), which indicated that there were no additional effects on the machine, such as vibrations or shifts in speed that could influence performance. The engineering stress-strain plots of the pure copper-tests with various thicknesses or samples depicted a level of stress necessary to initiate plastic flowing inside the material. From these results, we observed that strength and ductility declined with decreasing thickness. The influence of thickness on fracture-strain, observed during tensile testing, made it clear that the elongation-at-break of the pure-copper foils intensely decreased with decreases in thickness. The relative average surface-roughness Ra was evaluated, which showed us that the surface-roughness escalated with the increasing trend of plasticity deformation (plastic strain) ε. For better understanding of the effects of plastic strain on surface roughness prior to material fractures, micro tensile tests were performed on the newly developed machine under a 3D laser-confocal-microscope. We observed that homogeneous surface roughness was caused by plastic strain, which further formed the concave surface that led to the fracture points. Finally, we concluded that surface roughness was one of the crucial factors influencing the fracture behaviour of metallic sheet-strips in metal microforming. We found that this type of testing apparatus could be designed and manufactured within a manageable budget.