Crosshead Velocity Research Articles

An Interactive Fluid–Solid Approach for Numerical Modeling of Composite Metal Foam Behavior under Compression

Composite metal foams (CMF) are renowned for their high strength‐to‐density ratio, high stiffness, and energy absorption capabilities. Homogenized finite element models of CMF have been numerically solved to understand the mechanical behavior of the material under a variety of external loading conditions. This work aims to pioneer a comprehensive finite element model for steel–steel composite metal foam by incorporating the interactions between embedded stainless‐steel hollow spheres with entrapped air inside stainless‐steel matrix. The material behavior of hollow spheres, surrounding matrix, and air are modeled using Johnson–Cook (JC) plasticity, Deshpande–Fleck (D–F) foam, and linear polynomial equation of state in LS DYNA. Further, the finite element model utilizes a combination of Lagrangian solid elements and meshfree smooth particles hydrodynamics with appropriate contacts to effectively model the interaction of entrapped air within stainless‐steel hollow spheres with surrounding metallic spheres and matrix. The strain rate and the crosshead velocity of 65 s−1 and 2.4765 m s−1 are used for quasistatic compression analysis. Finally, the results obtained from the computational model are compared and validated using previously reported experimental quasistatic compression data. The numerical model corroborates stress–strain response of CMF with 5.6% error for plateau stresses average within 25% and 30% strain.

Impact of strain rate on mechanical properties of polylatic acid fabricated by fusion deposition modeling

AbstractThe primary objective of this research is to investigate the impact of strain rate on the mechanical properties of polylactic acid (PLA) fabricated through fused deposition modeling. PLA material was fabricated in a grid pattern with 75% infill density, a 0.16 mm layer height, and a ± 45° printing direction. This study specifically investigated tensile strength, flexural strength, and interlaminar strength with respect to varying crosshead speeds (1, 2, 3, 4, and 5 mm/min). The highest tensile strength noted was 40.13 MPa at a cross—head speed of 5 mm/min. Maximum elongation of 7.1% was noted on cross head velocity of 1 mm/min, and the maximum interlaminar strength reached 76.04 MPa at 4 mm/min. At a crosshead speed of 4 mm/min, the tensile strength measured was 38.36 MPa, which is a value close to the maximum result achieved in the tensile test. Interlaminar strength was notably higher at a crosshead speed of 4 mm/min, indicating a strong integrity of the printed layers. The values for elongation percentage and flexural strength were also moderate at a crosshead speed of 4 mm/min, which was 4.9% and 55 MPa, respectively. Therefore, crosshead speed of 4 mm/min appears to be an optimum factor for testing 3D printed PLA parts. This research sheds light on understanding the critical influence of strain rate in the mechanical performance of 3D printed PLA.

INVESTIGATING ENERGY ABSORPTION CAPABILITY OF ADDITIVELY MANUFACTURED CUBOCTAHEDRAL LATTICE STRUCTURES VIA TAGUCHI’S METHOD: EFFECTS OF PROCESS PARAMETERS

This research aims to investigate the influence of process parameters of fused filament deposition additive manufacturing technique on the energy absorption capacity of cuboctahedral lattice structures using Taguchi’s method. Four process parameters (i.e., print temperature, print speed, layer thickness, and line width) were considered with three levels of parameter values for each, which resulted in nine combinations in Taguchi’s L9 orthogonal array. The lattice structure was fabricated with each of nine combinations of process parameters and tested under a compression load to obtain the energy absorption experimentally. Signal-to-noise ratio analysis was conducted for the results obtained from the experiments of the nine Taguchi sets. Two more lattice specimens were fabricated with the parameter values which resulted in the best and worst energy absorption results and tested. The optimum values of the print temperature, print speed, layer thickness, and line width were determined to be 225 ºC, 30 mm/s, 0.12 mm, and 0.35 mm, respectively. The specific energy absorption (SEA) of the lattice specimen fabricated by using the optimum process parameter values presented 9.4% improvement compared to the highest SEA obtained from the lattices in the Taguchi’s L9 array.

Enhancing elongation and trading off strength versus ductility of commercially pure titanium sheets using cyclic bending under tension and annealing

This paper describes results acquired in an investigation into determining the influence of cyclic-bending-under-tension (CBT) and annealing on improving elongation-to-fracture (ETF) and optimizing strength and ductility of commercially pure titanium (cp-Ti) sheets. The space of process parameter involving crosshead velocity and bending depth along with sheet thickness was explored to establish a set of optimal parameters providing the greatest ETF for cp-Ti. Enhancements in ETF of about 3× were achieved using CBT relative to simple tension. Given the uniform elongation facilitated by CBT to very large strains, tradeoffs in strength and ductility of the material were examined by subjecting a set of sheets to a certain number of CBT cycles under the optimized parameters and annealing. In doing so, strength of the material increased by a factor of 1.6 along the sheet softest direction, while by a factor of 1.3 along the sheet strongest direction reducing the anisotropy. Microstructural evolution was characterized using electron-backscattered diffraction, while texture evolution was measured using neutron diffraction. These results revealed slip dominated deformation with minor activity of twinning. The role of CBT in preserving integrity of the sheets to large plastic strains is discussed by comparing measured and simulated geometries and mechanical fields.

Acoustic properties and low strain rate behavior of different types of chocolate

ABSTRACT Five different chocolate types (i.e. extra dark, dark, milk, white, and ruby) were characterized and compared for the acoustical and textural characteristics. Acoustic properties were described in terms of longitudinal and transversal wave velocities. These velocities were used for the evaluation of elastic constants namely Young modulus and Poisson ratio. The values of the Young moduli are significantly higher than those obtained using uniaxial compression and tensile tests. At the same time, the values of Poisson ratio are in reasonable agreement with results of these methods. Texture characteristics were evaluated using of the compression test at loading rates (crosshead velocity) 1, 10 and 100 mm/min. Results are presented in form of stress vs strain. The stress-strain dependences obtained from the compression test exhibited two different regions of the sensitivity of stress to the applied strain. The linear dependence stress- strain is taken as the evidence of the elastic behavior of the tested material. The extent of this region was given by the strain, which was the same for all tested chocolates. Its value increased with the loading rate. The stress-strain behavior in this region was only slightly dependent on the loading rate with exception of the ruby and dark chocolates. The stress-strain dependence in the following region was significantly dependent on the strain rate. Values of the strain rate sensitivity were evaluated. The order of the tested chocolates according to the values of stress at the given strain was identical with that obtained using of the elastic wave velocities.

Effect of strain rate on the compressive strength and texture of maraging steel grade 250

The present study demonstrates the effect of strain rates (in terms of cross head velocities of 0.1, 0.5 and 1 mm/min) during uniaxial compression test of cold rolled and annealed maraging steel (grade 250) on microstructure, texture and mechanical properties. The texture developed at lowest (0.1 mm/min) and highest (1 mm/min) strain rate facilitates the grains of the microstructure to take the equiaxed shape and bring some degree of uniformity as compared to the grains of starting (cold rolled and annealed) material. At intermediate (0.5 mm/min) strain rate the grains reorient towards the starting texture which provides a similarity in the microstructure of this and starting materials. The hardness and compressive strength at 15% total true strain of the alloy increases with increase in strain rates during the compression test. The role of texture in strengthening of compressed samples deformed with different strain rates as compared to the starting sample has been explained by the near Goss recrystallization component ((111) [1-1 0 ]) which is present in the starting material and remains absent in all the compressed samples. The (111)-fibre formation is observed to be an important phenomenon in this alloy. The (111)-fibre is strengthened in the starting material and the material compressed with 0.5 mm/min. The intensity of (111)-fibre becomes weaker for the samples compressed with lowest (0.1 mm/min) and highest (1 mm/min) strain rates and results in improved microstructure of the alloy.

Influence of Loading Speed on Tensile Strengths of Glass Fiber Reinforced Polymer Composite Experimental and Numerical Studies

The thermomechanical behavior of glass fiberreinforced polymer (GFRP) composite was studied. The thermal characteristics and the mechanical properties are determined over a temperature range from ambient to 60°C. The calcium carbonate filler of the amount 15% of the weight of the resin have been used in order to improve the mechanical proprieties and attempt to observe the possibility of replacement a part of expensive resin by cheap filler. The loading speed refers to the crosshead velocity, which has direct Proportionality with strain rate. After the specimens are exposed to temperatures ranging from 20 , 40 to 60 , the results show a greater elongation indicate a greater ductility that explain we improved the tenacity of specimens, Especially for temperature 60, this propriety is more suitable for vehicle industry. Results in terms of simulation using a code program (Abaqus) are presented, The Johnson–Cook (JC) model was chosen as the constitutive model and then the finite element solutions were compared to the experimental results. A good agreement of the numerical curves with the target loading curves was found.

Cyclic bending under tension of alloy AZ31 sheets: Influence on elongation-to-fracture and strength

This paper describes the main results from an experimental investigation into the consequence of cyclic bending under tension on elongation-to-fracture (ETF) and strength of AZ31 sheets. The deformation is imparted on test specimens of the alloy using a recently built continuous-bending-under-tension (CBT) apparatus conceived to increase ETF relative to simple tension (ST). The apparatus pulls the specimen in tension with a certain velocity while the specimen reciprocates through a set of three rollers, which impart a given amount of bending. The parameter space consisting of bending depth, crosshead velocity, and sheet thickness is explored to achieve the greatest ETF for the alloy. However, only moderate improvements in ETF are obtained. The small improvements are attributed to the relatively uniform elongation of the alloy during both CBT and ST with a small amount of the remaining ductility to deplete throughout the sheet by CBT after exhausting the uniform elongation. Measurements of the grain structure and texture evolution using electron-backscattered diffraction and neutron diffraction reveal slip dominated deformation with some twinning followed by de-twinning. The behavior of the alloy upon CBT processing to a certain number of CBT cycles followed by heat treatments (HT) is also investigated to achieve tradeoffs in strength and ductility. Results and insights from these investigations are presented and discussed. Significantly, it is shown that the strength of the alloy can be increased for over 30% while preserving at least 5% of its ductility.

Micro-mechanical and X-Ray micro-computed tomographical analysis of quasi-static three-point loading behaviour of closed-cell aluminium foam with and without epoxy-bonded aluminium face-sheet

Abstract A quasi-static three-point loading experiment of closed-cell aluminium foam without face sheet (CCA) and closed-cell aluminium foam with face sheet (CCAF) was performed. During the experiment, load-deformation curves of CCA and CCAF foams were monitored for varying span length and crosshead velocity. CCA and CCAF foam maximum loading capacity were around 283.41 N and 1633.76 N, respectively. The effect of facesheet on the morphological and elemental inhomogeneity was analysed and related to understand the foam failure behaviour. It was observed that the presence of high strength epoxy-bonded face sheet prevented the tensile zone fracture in CCAF foams as compared to CCA foams. Micro Computed Tomographical analysis showed adjacent undeformed cells of the fractured region of CCA foams. CCA foams showed ductile-brittle mode with brittle dominating failure mode. In contrast, CCAF foams showed the gradual pore deformation and mixed deformation mode with initial indentation followed by the core shear process. Microstructural, elemental, and phase analysis of the failed zone showed micro-cracks, micro dimples, and ridges present in the foam core's cell wall. Ca–Ti–Al precipitates and intermetallics were present in plateau and cell wall regions. These precipitates act as reinforcement to the cell wall's strength during compression (as in CCAF foams). However, in tensile loading zone, they acted as a centre of crack initiation (as in CCA foams).

On the activation energy for plastic flow during tension test at room temperature and the anisotropy behaviour of Ti-6Al-4V alloy

The movement of dislocations inside of crystals during the tension test at constant crosshead velocity is related to activation energy for plastic flow in spatially extended polycrystalline systems. In this work, the main objectives are to establish the influence of the slip systems for α hexagonal compact packaging (hcp) titanium phase on the activation energy for plastic flow and the anisotropy influence on the plastic flow behaviour of Ti-6Al-4V alloy in sheet form under tension test at constant crosshead velocity of 1 mm/min in three in-plane orientations, namely in the rolling 0° (RD), 45° (DD) and transverse (TD) directions, respectively. By applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade, it is shown that for a <c+a> pyramidal type slip with a Burgers vector b=0.553 nm, the activation energy barrier for plastic flow at maximum stress in uniaxial tension in the sheet rolling direction, Q=115.115 kJ/mol is lower in comparison with Q=116,629 kJ/mol obtained by the <a> basal type slip with a Burgers vector b=0.295nm. These results are in accordance with the reduced cross-slip activation energy barrier for cross-slip onto pyramidal planes in an a hexagonal crystalline structure with compact packaging (hcp) titanium phase. Additionally, it was shown that transverse direction (TD) of Ti-6Al-4V alloy in sheet form has developed the maximum stress in uniaxial tension test and ductility.

Investigation and optimization of Superplastic forming parameter in Aluminium alloy

Super plasticity is the capability of materials to parade very high tensile elongation which can be more than 2500%, appearing in eminent temperature under low stress dependent on strain rate. In this paper intentions to optimize superplastic parameters such as yield stress, ultimate stress, temperature, strain rate and strain rate sensitivity index by using hot tensile test method in AA 7075 alloy in experimental and numerical simulation method. In experimental method, the cross head velocity concept has been adopted to attain the permeability by achieving the material properties with the functions’ of temperatures conditions. Finite element method using ABAQUS software was modeled to compare the experimental results.

Experimental and numerical analysis of the heat generated by plastic deformation in quasi-static uniaxial tensile tests

This study evaluates the temperature variation observed in quasi-static uniaxial tensile tests, due to the heat generated by plastic deformation. The AA6016-T4 aluminium alloy was the material selected, considering different values of crosshead velocity (from 0.01 mm/s up to 1 mm/s). The temperature variation was also evaluated during the stress relaxation test. A finite element model of the uniaxial tensile test is presented, which takes into account the heat generated by plastic deformation, as well as the effect of the heat losses to the environment (convective heat transfer coefficient) and to the grips (interfacial heat transfer coefficient). The numerical results show that the predicted temperature variation is almost independent of the selected heat transfer coefficients. On the other hand, the temperature rise is influenced by the Taylor–Quinney coefficient. The comparison between experimental and numerical temperatures shows that the Zehnder model (increasing Taylor–Quinney coefficient) provides more accurate results than the Aravas model (decreasing Taylor–Quinney coefficient). Nevertheless, the evolution of the Taylor–Quinney coefficient defined by the Zehnder model assumes a constant value for the hardening coefficient, which does not fit the hardening behaviour observed for this aluminium alloy.

Evaluation and characterisation of ASS316L at sub-zero temperature

ABSTRACT Austenitic Stainless-Steel grade 316L is one among the significant ASS grades which is most used in various industry sectors. It has excellent corrosion resistance in ordinary atmospheric and in more arduous environments such as saltwater. Whilst performing well when exposed to relatively high temperatures, this grade of ASS also maintains its strength and toughness at sub-zero temperatures, making this an excellent choice for various applications in industrial sectors such as Marine, general construction and water treatment. Therefore, present study focused on evaluating the mechanical properties, ultimate tensile strength (UTS), yield strength (YS) and strain hardening exponent (n) are evaluated based on the experimental data obtained from the uniaxial isothermal tensile tests performed at an interval of −25°C from 0°C to −50°C and at three orientations 0, 45, 90 degrees to the rolling direction and cross-head velocity 3, 5, 7 mm/min were chosen. Total of 27 experiments have been planned based on design-of-experiments. A mathematical model for the prediction of UTS, YS and n was developed using process parameters such as temperature, orientation and cross-head velocities. Results have shown that mechanical properties can be predicted with a reasonable accuracy within the range of process parameters considered in this study.

Experimental studies into the role of cyclic bending during stretching of dual-phase steel sheets

Continuous-bending-under-tension (CBT) has been conceived as a mechanical test or a forming process imparting cyclic bending during stretching of a metallic sheet or strip in order to increase its elongation to fracture (ETF) relative to simple tension (ST). In a recent work, over five times improved ETF by CBT over ST has been reported for a dual-phase (DP) steel DP 1180. This paper evaluates the behavior in CBT of three additional automotive advanced high strength steels (AHSS), DP 590, DP 780, and DP 980. In doing so, the process parameter space defined in terms of crosshead velocity applying the tensile force, and roller depth imposing the amount of bending to the specimen has been explored to maximize the ETF of these materials. The studied steel sheets had different thicknesses, in addition to intrinsically containing different fractions of ferrite and martensite phases. After establishing the optimal process parameters, significant improvements in ETF are achieved for all studied steels. Based on comprehensive data, it is found that lower martensitic content moderately improves ETF, while increasing of the sheet thickness rapidly deteriorates ETF, under CBT. The behavior in tension of sheets that were subjected to CBT processing under the established optimal process condition is investigated to determine enhancement in strength and any residual ductility of the materials. In addition to testing, a combination of electron microscopy along with electron-backscattered diffraction and neutron diffraction is employed in order to assess the initial microstructure, evolution of crystallographic texture, and fracture mechanisms for the studied steels. Texture evolution in CBT forms a more pronounced {011} fiber along the stretching direction than in ST, revealing that the deformation in CBT could extend to greater strain levels than those reached at the fracture location in ST. Fractured surfaces after CBT are found to consist of fine ductile dimples, while those after ST consist of coarser dimples and some content of brittle flat martensitic regions.

Testing of Formed Gear Wheels at Quasi-Static and Elevated Strain Rates

Geared components can be manufactured from sheet metals by sheet-bulk metal forming. One relevant load case in service are overload events, which might induce elevated strain rates. To determine the characteristic hardening and fracture behavior, specimens manufactured from the deep-drawing steel DC04 were tested with strain rates ranging from 0.0001 to 5 s−1. The gear wheels manufactured by sheet-bulk metal forming are tested at crosshead velocities of 0.08 mm/s and 175 mm/s. The tests are analyzed by measuring deformed geometry and hardness. While the tensile tests results show obvious strain-rate dependency, the hardness measurements show no strain-rate depended effect. The analyses are complemented by finite-element-simulations, which assess the homogeneity of deformation and point out the mechanisms of failure. Both coupled and uncoupled ductile damage models are able to predict the critical areas for crack initiation. The coupled damage model has slight advantages regarding deformed shape prediction.

Picture-frame testing of woven prepreg fabric: An investigation of sample geometry and shear angle acquisition

This paper examines different concepts in relation to the picture-frame test for shear characterization of a woven prepreg fabric. The influence of the sample arms is investigated by means of cut slits as well as removed transverse tows. Shear angles are obtained using Digital Image Correlation (DIC) and also from images taken during the test which are processed for fiber angles directly from the weave texture. The image processing relies on the Hough transform in MATLAB. The concept of constant shear strain rate is discussed and implemented in the test software by a multi-linear crosshead velocity profile. Finally, bias-extension data are obtained and used for comparison. It is found that the sample arm modifications have a pronounced effect on the measured shear load whereas the uniformness of the shear strain field in the samples is not improved considerably.

Energy dissipation accompanying Mullins effect of nitrile butadiene rubber/carbon black nanocomposites

Mullins effect of carbon black filled nitrile butadiene rubber compounds and vulcanizates during cyclic tensile deformation is investigated and the influences of thermal annealing of the stretched samples, the deformation velocity and history and the solvent swelling are discussed. The energy losses associated with recovery hysteresis and softening accompanying the Mullins effect at a given crosshead velocity are quantitatively analyzed. The results show that the recovery hysteresis involves in microscopic deformation of the rubber phase in the nanocomposites but it disappears in the swollen samples. On the other hand, the softening is associated with both the rubber and filler phases; its energy loss increases with increasing filler content and decreases significantly by swelling. Furthermore, the softening of samples stretched at room temperatures is recoverable after conditioning at 80 °C but the recovery is retarded significantly by filler. The investigation allows gaining recognition of the important role played by the viscoelastic rubber matrix and the influence of the filler.

Evaluation and Optimization of Material Properties of Brass at Subzero Temperature Using Taguchi Robust Design

Abstract Copper and its alloys are the most versatile engineering materials, offering a wide range of mechanical properties such as strength, machinability and ductility that make them uniquely suited to a vast number of applications. In the present study, an extensive work has been carried out to quantify the tensile properties of brass at subzero temperatures with different crosshead velocities in three orientations. The process parameters plays a major role in this investigation, the three low temperatures were 0°C, -25°C, -50°C, the three cross head velocities were 3, 5, 7mm/min and the three orientations such as 0, 45, 90 degrees. The main objective of this work is to optimize these process parameters by using Taguchi method and to anticipate the optimum tensile properties such as ultimate tensile strength, yield strength and % of elongation. L9 orthogonal array was selected to conduct the experiments based on Taguchi robust design and to study the influence of various combinations of process parameters on tensile properties of brass. Data collected from Taguchi experiments were analyzed and optimum condition was reported. In addition to that Analysis of Variance (ANOVA) was carried out to determine the significance of each process parameter for finding tensile and percentage elongation behaviour of brass material.

Experimental study of continuous-bending-under-tension of AA6022-T4

This paper presents an experimental setup for continuous-bending-under-tension (CBT) of thin strips and sheets, aimed at the investigation of the observed elongation-to-fracture (ETF) enhancements under such conditions. In particular, the kinematics of the process are described and correlated with the evolution of axial force measured during testing. The main results of the effect of process parameters, such as crosshead velocity and bending depth, on the ETF and the reduction of axial force are presented for the aluminum alloy AA6022-T4. The force vs. displacement response is not found to be a strong function of the crosshead velocity, which is explained by the near rate-independence of the material in the strain-rate range that occurs in CBT. Similarly, ETF does not show a clear dependence on the bending depth or the crosshead velocity. On the other hand, the axial force decreases linearly with the bending depth and slightly increases with the velocity. From the detailed analysis, the optimal parameters for enhancing ductility of AA6022-T4 under CBT are 1.2 mm/s for crosshead velocity and 2.0 for normalized bending depth. Under these conditions, a significant finding is that the strain level achieved throughout the CBT specimen is comparable to that in the necked region of a specimen tested to rupture in uniaxial tension.

Over five-times improved elongation-to-fracture of dual-phase 1180 steel by continuous-bending-under-tension

This paper reports the main results from an experimental investigation into the improved elongation-to-fracture (ETF) of the advanced high strength steel (AHSS) dual-phase (DP) 1180 by subjecting the material to the continuous-bending-under-tension (CBT) process. The investigation is carried out using a recently developed testing apparatus, where the specimen flows in a reciprocating fashion through a set of three rollers while it is continuously pulled in tension. The process parameters such as the roller depth defining the amount of bending and wrapping around the rollers and crosshead velocity applying the tensile force to the specimen are varied to maximize the ETF of the material. From the recorded force vs. displacement curves along the rolling direction (RD), 45°, and transverse direction (TD), ETF of DP 1180 is found to improve with the crosshead velocity and with the bending depth up to a certain level, after which it decreases. The optimal parameters of 1.35 mm/s for the crosshead velocity and 3.5 for the normalized bending depth improve ETF of the material over five times in every testing direction relative to simple tension tests. The role of CBT in preserving high integrity of the material to large plastic strains is discussed.