Strain Rate Sensitive Material Research Articles

Effects of mandrel velocity on residual stresses created in cold expansion process of adjacent holes for AA6016-T6 and AA1100 aluminum alloys

Cold expansion is a mechanical method for creating residual stresses. This method is a proven technique to increase the fatigue life, and checking the residual stress on it, is of particular importance. A cold expansion process is widely used to generate beneficial residual stresses into an annular region around the hole. In the present research work, AA 6016-T6 and AA 1100 aluminum alloys which are two strain rate sensitive materials, were subjected to cold expansion process with different mandrel velocities. In fact, the effect of mandrel velocity on the created residual stresses has been investigated. The constants of the Johnson-Cook material model have been determined for them and the process has been investigated, experimentally and numerically. The obtained results revealed that the values of the residual stresses created in the sheets depend on the velocity of the process especially at the edge of the sheets holes. By increasing the mandrel velocity from 5 to 500 mm/min, depending on the distance from the hole to the edge of the sheet, it is possible to enhance the hoop residual stress by 37.3–41.2% in AA 1100 aluminum alloy and by 37.6–38.1% in AA 6016-T6 aluminum alloy. This research showed that in all cases, the radial residual stresses created around the holes are negative. Also, it was cleared that due to the existence of material constraints and the movement of the sheet material, the amount of hoop residual stress created in the mid-thickness is more than the exit face and in the exit face is also more than the entrance face, exactly unlike the size of their zones.

Validation of Experimental Data for the Application of the Magnesium Alloy “Elektron 43”

The behaviour of a structural component, such as the spreader installed on an aeroplane passenger seat made of the magnesium alloy Elektron® 43, is evaluated under a variety of load conditions. The purpose of this research project is to considerably reduce weight by employing the new alloy while keeping the strength and ductility necessary to meet the dynamic standards for both the 16 g forward and 14 g downward tests. A comprehensive campaign of static and dynamic testing on coupons was conducted to characterise the mechanical behaviour of the E43 magnesium alloy, from quasi-static to dynamic loading, and across a wide range of deformation rates. The elastic–plastic and strain rate sensitive material model of E43 is then calibrated using an FEA approach and LS-DYNA software, utilising stress–strain curves and properties determined from standardised experimental tensile and compression trials at varied strain rates. Finally, this material model was used to perform a finite element structural study of a major component of an aeroplane seat built using Elektron® 43 under typical in-flight stresses.

Strain rate effect of concrete based on split Hopkinson pressure bar (SHPB) test

Concrete is a strain rate sensitive material, which is widely used in protective structures, and its strain rate effect needs to be considered. This study aims to obtain the real strain rate effect of concrete material. Firstly, the dynamic compression test of concrete was carried out by using split Hopkinson pressure bar (SHPB). The classical Holmquist-Johnson-Cook (HJC) model of concrete is modified based on the test results and the test data of the static performance of concrete. Then the finite element model is established. The numerical simulation results and theoretical analysis show that the inertia effect leads to the error between the test value and the simulation value. To eliminate the influence of inertia effect, this study embeds the inertia effect term into the constitutive model for secondary modification. According to the results of numerical analysis, the specific form of this term and its related parameters are determined. The modified constitutive model can better predict the test results and reproduce the damage morphology of concrete under impact load.

Highly strain-rate sensitive and ductile composite materials combining soft with stiff TPMS polymer-based interpenetrating phases

The current work investigates the engineering of strain-rate sensitive and ductile composites through the combination of stiff, triply-periodic-minimal-surface (TPMS) with soft, rubber-type material phases. Different interpenetrating phase composite (IPC) designs are considered, with Diamond, Fisher-Koch, and IWP TPMS architectures as reinforcement phase topologies. The loading rate sensitivity of the arising IPCs is evaluated at different strain-rates, revealing an effective composite performance that well separates from the either brittle or substantially low-strength behavior of its constituent materials. Significant strain-rate effects are recorded, which relate to increased stiffness and energy absorption attributes upon substantial ductility, with the actual performance to depend on the underlying reinforcement phase topology. The effective strain-rate IPC constitutive response is well-captured by dedicated, low numerical cost and high accuracy machine learning models, whereas Digital Image Correlation (DIC) and finite element analysis are employed to provide insights in the inner strain and stress fields developed and failure modes observed. Overall, energy absorptions higher than 10 and up to 14 MJ m−3 are reported for strain-rates in the order of 100, furnishing specific energy absorptions (SEA) in the uppermost range of the effective composite material behaviors up to now reported, upon exceptionally high crushing force efficiencies (CFE) at moderate densities.

Dynamic tensile mechanical properties of 18Ni350 maraging steel fabricated by wire arc additive manufacturing

The dynamic tensile mechanical properties of 18Ni350 maraging steel (M350) fabricated by wire arc additive manufacturing (WAAM) was investigated by the split Hopkinson tensile bar (SHTB) and microstructural analysis. The results show that the yield stress (YS) of M350 samples, both in as-built and heat-treated state, increases firstly and then decreases with increasing strain rate. The YS of the as-built sample reaches the maximum value of 2195 MPa at 1230s−1, and that increases to 3395 MPa after heat treatment, due to the precipitation of intermetallic. Compared with the sample in the horizonal direction, the sample in the vertical direction exhibits a higher dynamic strength, due to the preferred growth of columnar crystal along the vertical direction during WAAM process. Under dynamic load, the retained austenite transformed into martensite and the oxide inclusions are cracked, resulting in a heterogeneous fracture morphology. Based on those results the hardening model and the anisotropic model of the strain rate sensitive material fabricated by WAAM were established. The results can provide a guidance for the reliability evaluation of maraging steel fabricated by WAAM under dynamic load conditions.

Effects of Strain Rate and Fiber Content on the Dynamic Mechanical Properties of Sisal Fiber Cement-Based Composites

In this paper, a split Hopkinson pressure bar (SHPB) was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites (SFRCCs), and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS). The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials. Compared with ordinary cement-based composites (OCCs), the SFRCCs demonstrate higher post-peak strength, ductility, and energy absorption capacity with higher fiber content. Moreover, the SFRCCs are strain rate sensitive materials, and their peak stress, ultimate strain, and energy integrals all increase with increasing strain rate. From the perspective of fracture failure characteristics, the failure of OCCs is dominated by the brittle failure of crystal cleavage. In contrast, the failure mode of the SFRCCs changes to microscale matrix cracks, multi-scale pull-out interface debonding of fibers (fine filaments and bundles), and mechanical interlock. This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.

Investigation of impact performance of perforated plates and effects of the perforation arrangement and shape on failure mode

Searching for lighter protective structure and better energy absorption material is the key goal to improve the protection performance of moving platforms. The impact performance of perforated structures subjected to projectile impact and effects of the perforation arrangement and shape on failure mode are investigated experimentally and numerically. Three different impact velocities, three kinds of hole patterns (circle, triangle and square) and two types of hole arrangements (matrix type and dislocation type) of the perforated plate specimens are discussed in this research. The Mie-Grüneisen equation of states and Johnson-Cook strain-rate sensitive material models are selected in the numerical model. The numerical results agree well with the experimental results. The results show that when the impact velocity, hole shape and hole arrangement are different, the failure modes of perforated plate and witness plate can be divided into eight and four modes, respectively. The projectile deflection effects are observed when the projectile passes through the perforated plate. The deviation angle of projectile decreases with the increase of impact velocity. The deviation angle of perforated plate with circle hole and triangle hole by dislocation type is greater than that by matrix type at the same impact velocity, but the conclusion of perforated plate with square hole is just the opposite. The ballistic deflection effect of the perforated structure with triangular hole is greater than that with the circular hole and square hole. The results obtained from the study will provide a reference to the research of new spatial or layered armor systems containing the perforated plates.

Shock Response of Porcine Meniscus along with Axial and Radial Directions

The meniscus is a multifunctional fibrocartilage tissue in the knee joint which stables joint movement, bears load and absorbs impact. Improper collisions will cause damage to meniscus tissue and lose its original functionality. However, it is difficult to fully evaluate the mechanical properties of the meniscus based on static test results alone. In this study, Split Hopkinson Pressure Bar (SHPB) and hydraulic material testing system (MTS) were utilized to examine the quasi-static and dynamic properties of the porcine meniscus along with two different orientations. The results showed that the meniscus is a strain rate sensitive material and its mechanical properties mainly depend on the orientation of collagen fiber bundles in the peripheral direction. The meniscus tissue did not show obvious yield characteristics under quasi-static test conditions. However, the meniscus showed clear yield behavior under dynamic loading. When the strain rate increased, the elastic modulus of the radial meniscus remained around 35 MPa while the elastic modulus of the axial meniscus increased from 30 MPa to 80 MPa. This study demonstrates that the meniscus is sensitive to strain rate at both dynamic and quasi-static conditions, and the meniscus is an anisotropic biological tissue.

A Fundamental Study on Compression Properties and Strain Rate Sensitivity of Spray-Dried Amorphous Solid Dispersions

Amorphous solid dispersions (ASDs) are a proven method of improving the solubility and bioavailability of poorly soluble compounds. Immediate release tablets are frequently used as final dosage form for ASDs. Increasing tableting process throughput during clinical development requires using larger, faster tablet presses which subject materials to higher strain rate. Many pharmaceutical materials show strain rate sensitivity, i.e., yield pressure sensitivity to compression speed. Currently, there is only scattered information available in scientific literature on how ASDs behave under different tablet compression speeds. The purpose of this study was to examine spray-dried ASDs' sensitivity to strain rate under compression in a comprehensive study. We also investigated the drivers for such a strain sensitive behavior. A set of sample spray-dried powders, selected for their range of properties, were compressed using a simulated Korsch XL100 profile at 3 and 30 RPM and V-profile at 0.1 and 300mm/s on a Phoenix compaction simulator. The sample set included samples with varying API content (0-50% w/w), stabilizing polymer (HPMC, HPMC-AS, PVP-VA), particle size, and bulk densities, produced on spray driers from lab to commercial scale. We identified that all ASD samples showed plastic flow and deformation behavior and form robust compacts at slow compression speeds. At high speed, tablet defects occurred. The strain rate sensitivity observed in this study was comparable or slightly superior to that observed for microcrystalline cellulose, known to be a mildly strain rate-sensitive material. We showed that compression speed is a critical process parameter for ASD-containing tablets.

Microstructure and Thermal Deformation Behavior of Hot-Pressing Sintered Zr-6Al-0.1B Alloy.

Zr-6Al-0.1B alloy rich in Zr3Al phase is prepared by hot-pressing sintering. The thermal deformation behavior of sintered Zr-6Al-0.1B is analyzed by isothermal compression tests at deformation temperatures of 950, 1050, and 1150 °C with strain rates of 0.01, 0.1, and 1 s−1. The results indicate that at the early stage of thermal deformation, the stress increases rapidly with the increase of strain and then reaches the peak value. Subsequently, the stress decreases with the increase of strain under the softening effect. On the whole, the true stress-strain curve shifts to the high stress area with the increase of strain rate or the decrease of deformation temperature, so the sintered Zr-6Al-0.1B alloy belongs to the temperature and strain rate sensitive material. For the microstructure evolution of sintered Zr-6Al-0.1B during the isothermal compression, the high strain rate can improve the grain refinement. However, because sintered Zr-6Al-0.1B is a low plastic material, too high strain rate will exceed the deformation capacity of the material, resulting in an increase in defects. The increase of deformation temperature also contributes to grain refinement, but when the temperature is too high, due to the decomposition of Zr3Al phase, the deformation coordination of the material decreases, leading to the increase of the probability of the occurrence of defects. This study verified the feasibility of hot-pressing sintering to prepare Zr-6Al-0.1B alloy rich in Zr3Al phase and laid the foundation of “hot-pressing sintering + canning hot-extrusion” process of Zr-6Al-0.1B alloy components.

Experimental research on the compressive properties of a new type three-dimensional angle-interlock woven composite

The new three-dimensional angle-interlock woven UHMWPEF/epoxy composite was prepared by the VARIM method, and its mechanical properties were studied. Specifically, quasi-static and dynamic compression tests were carried out by universal testing machine and split Hopkinson pressure bar (SHPB) apparatus. Stress-strain curves under the quasi-static and high strain rates (800, 1000, 1400, and 1600 s−1) reveal the destructive characteristics of the composite material. The results indicate that the UHWMPEF/epoxy composite is a strain rate sensitive material and shows different levels of sensitivity at various strain rates. In the quasi-static compression test, when the strain rate was increased from 4.2 × 10−4 to 1.4 × 10−3 s−1, the failure load and ultimate strength increased by about 19.1% and 20.1%, respectively, and the failure strain and specific energy absorption decreased by about 1.53% and 6.1%, respectively. In the dynamic compression test, when the strain rate increased from 800 to 1600 s−1, the failure load and ultimate strength increased by about 16% and 15.9%, respectively, and the failure strain and specific energy absorption decreased by about 64.7% and 60.3%, respectively. The failure fracture surface of the specimen under quasi-static compression was at an angle of 40°–45° with the load direction. The matrix fragmentation at the fracture was obvious, and the warp fiber bundle was broken and peeled off from the matrix. The damage of specimen under dynamic compression develops quickly and the deformation process is short, which shows a relatively symmetrical shear fracture failure morphology.

Dynamic Response of Electro-Mechanical Properties of Cement-Based Piezoelectric Composites

By employing ordinary Portland cement as a matrix and PZT-5H piezoelectric ceramic as the functional body, 1-3 and 2-2 cement-based piezoelectric composites were prepared. Quasi-static compression tests were performed along with dynamic impact loading tests to study the electro-mechanical response characteristics of 1-3 and 2-2 cement-based piezoelectric composites. The research results show that both composites exhibit strain rate effects under quasi-static compression and dynamic impact loading since they are strain-rate sensitive materials. The sensitivity of the two composites has a non-linear mutation point: in the quasi-static state, the sensitivity of 1-3 and 2-2 composites is 157 and 169 pC/N, respectively; in the dynamic state, the respective sensitivity is 323 and 296 pC/N. Although the sensitivity difference is not significant, the linear range of the 2-2 composite is 24.8% and 61.3% larger than that of the 1-3 composite under quasi-static compression and dynamic impact loading, respectively. Accordingly, the 2-2 composite exhibits certain advantages as a sensor material, irrespective of whether it is subjected to quasi-static or dynamic loading.

Hot compression deformation behavior and constitutive model of 2050 Al-Li alloy

Isothermal compression experiments of 2050 AL-Li alloy were carried out by Gleeble-3800 thermal-mechanical simulator. Hot compression deformation behavior of the alloy under the conditions of deformation temperature of 300~500 °C and strain rate of 0.01~10 s-1 was studied. The constitutive model of thermal deformation was established. Results indicate that there is an obvious rheological steady state in the isothermal compression process of 2050 aluminum alloy. The microstructure shows that the alloy has recrystallization. 2050 aluminum alloy is a positive strain rate sensitive material. At constant temperature, the steady state flow stress increases with the increase of strain rate. Arrhenius constitutive model can accurately predict the rheological behavior of 2050 aluminum alloy. The average absolute relative error (AARE) of the relative error between the experimental value and the predicted value is 8.59%.

Dynamic recrystallization behavior and microstructure evolution of low-density high-strength Fe–Mn–Al–C steel

The hot deformation behavior of low-density high-strength Fe–Mn–Al–C steel at T = 900–1150 °C and ε˙ = 0.01–10 s−1 is studied using the Gleeble-3500 thermo-mechanical simulator. The rheological stress curve characteristics of the steel are analyzed through experimental data and the dynamic recrystallization activation energy is calculated. The critical strain/stress, peak strain/stress and steady-state strain/stress models of dynamic recrystallization are characterized by introducing the dimensionless parameter Zener-Hollomon. The microstructure evolution is analyzed and the dynamic recrystallization state diagram of the steel is drawn. The results indicated that the steel is a negative temperature-sensitive and a positive strain rate-sensitive material. The dynamic recrystallization activation energy is 669.844 kJ mol−1. With the decrease of ε˙ or the increase of T, the Z parameter decreases gradually and the dynamic recrystallization behavior is more likely to occur; however, its grain size increases accordingly. The fine and uniform grain structure can be obtained by hot working in the range of 950–1000 °C/0.01–0.1 s−1 and 1050–1100 °C/1–10 s−1. Finally, the prediction model for the dynamic recrystallization average grain size is established, and the correlation coefficient (R) of the prediction model is 0.996; therefore, the model has a high prediction accuracy.

Material similarity of scaled models

When different strain hardening, strain-rate sensitive and temperature softening materials are used for scaled model and prototype, the traditional similarity laws of solid mechanics will be broken. Although research works in the last twenty years have developed the correction methods of initial conditions to compensate for the similarity distortion, their basic correction factors are practically impeded for their inherent non-direct (depending on unknown structural responses) and inexact (having significant similarity errors) defects. In this paper, a more complete framework of material similarity is developed. Based on the similarity analysis of thermo-visco-plastic constitutive equation, the material dimensionless numbers are suggested to represent the objective similarity of strain hardening, strain-rate sensitive and temperature softening effects. The universal direct and exact solution of the basic correction factors is further proved when the material numbers of the scaled model and the prototype are equal, which overcomes the previous inherent defects radically. And the simple and practical phase diagram of ‘material numbers - strain/strain-rate/temperature’ curves are proposed to design the optimum similitude materials. Three impacted structure are numerically verified: circular plate, crooked plate, and Taylor bar. The results show that the proposed material numbers control the similarity behavior of different materials. When the proposed direct and exact methods are used by the designed optimum similitude materials, the completely different materials can behave acceptable exact similarity of strain, strain-rate, temperature, stress and displacement responses in time and space fields.

Exploring the impact of CoFe2O4 additives morphology on the properties of a novel strain-rate sensitive composite material

Various additives in smart materials are attracting wide attention owing to the improved adaptable functions, such as the ferromagnetic additive. However, the effect of additives’ morphology is not well investigated, causing inconsistent phenomena reported for the same additive. In this work, the spherical and rod-shaped CoFe2O4 nanoparticles were prepared by varying the reaction process of solvothermal, and introduced as dispersed phases into strain rate-sensitive materials to fabricate new strain-rate sensitive composite materials. The influence of magnetic particle morphology on its rheological performance was investigated. The results showed that the strain-rate sensitive composites with rod-shaped CoFe2O4 (RCFO) have a higher storage modulus and viscosity than the ones with spherical CoFe2O4 (SCFO) nanoparticles. The relationship between shear rate and viscosity indicates that all samples exhibited significant shear thinning effects in the range of shear rates studied, and the RCFO nanoparticles are useful for achieving a higher viscosity in comparison to the SCFO nanoparticles at the same shear rate. This work proves that the morphology of additives plays an important role in adjusting the property of smart materials and is expected to present some principles to choose the suitable morphology of additives for the design of new magneto-rheological materials.

Hot Deformation Behavior of 980MPa δ-TRIP Steel

The δ-TRIP steel has attracted wide attention from researchers and industry, as it possesses the mechanical properties of the third-generation advanced automotive steels, and the lower density achieved by the addition of light element aluminum. However, there have been few studies on the hot deformation behavior of δ-TRIP steel at high temperature, which is critical for the design of the hot rolling process. In the present study, hot compression tests were carried out on a 980 MPa δ-TRIP steel to achieve a better understanding of the deformation behavior at high temperatures from 800°C to 1150°C. Combined with the electron backscatter diffraction (EBSD) analysis, the results showed that δ-TRIP steel was a positive strain-rate sensitive material, and its soften was contributed by dynamic re-crystallization of ferrite and austenite during deformation at high temperature. The hot deformation activation energy (Q = 327.485 kJ/mol) of the experimental steel was calculated, and the strain index was 5.65. Besides, the related constitutive equation and the flow stress equation were also established.

Hot deformation characterization of Ti–Nb alloy based on GA-LSSVM and 3D processing map

Abstract The thermal compression tests of Ti–Nb alloy under T = 790–940 °C and e ˙ = 0.001–10s−1 were carried out on the thermal simulation testing machine of Gleeble-3500. The flow stress curves were obtained, and the high-temperature rheological properties of the alloy were analyzed. The 3D activation energy maps were calculated and constructed. The LSSVM model of constitutive relation was established, and the penalty coefficient γ and kernel parameter δ of the LSSVM model were optimized by the genetic algorithm (GA). The constitutive model of the alloy based on the GA-LSSVM algorithm was constructed. The predicted value of the model was also compared with the experimental data. The polar reciprocity model (PRM) and dynamic material model (DMM) were used to establish the 3D processing map of the alloy and appropriate thermal processing parameters. The results indicated that T and e ˙ have a great influence on the flow stress of Ti–Nb alloy. Ti–Nb alloy is a negative temperature-sensitive and a positive strain rate-sensitive material. The correlation coefficient (R) of the GA-LSSVM algorithm constitutive model is 0.9958. The model has high prediction accuracy and strong generalization ability, which provide a new method for establishing a high-temperature constitutive model of materials. The PRM processing map is more accurate in optimizing the processing parameters of Ti–Nb alloy than that of the DMM processing map through analyzing the 3D processing map and observing the microstructure. The instability modes in the instability region of the alloy mainly include local flow. The stability region's predominant deformation mechanism is DRX. The 870–940 °C and 0.001–0.01s−1 are the best parameters during the processing of Ti–Nb alloy.

Experimental study on the tension and puncture behavior of spray polyurea at high strain rates

Polyurea is widely used as a protective coating material for structures subjected to impulsive loads. In this study, the mechanical properties of polyurea were investigated experimentally over a wide range of loading rates. Firstly, quasi-static tests were performed using conventional hydraulic machine at strain rates of 7.7 × 10−4 - 7.3 × 10−3 s−1 for direct tension and at speeds of 1.67 × 10−5 - 1.67 × 10−4 m/s for puncture. Then high-speed tests were carried out using a high-speed servo-hydraulic testing machine (INSTRON VHS 160/100-20) at strain rates of 3.3–500.3 s−1 for direct tension and at speeds of 0.1–10 m/s for puncture. Deformation and failure processes of the polyurea specimens under high-speed tension were recorded with the aid of a high-speed camera. The testing results show that polyurea is a strain rate sensitive material. Under tensile loads, the initial yield stress and the strength increase with the increment of the strain rates while the fracture strain decreases. Under puncture loads, the yield force and the strength of the polyurea sheets also increase with loading rates. However, the strain rate effect on the failure deformation of the polyurea is only observed when the loading rate is less than 2 m/s. Based on the testing data, mechanism that causes the dynamic effect of polyurea material properties was discussed and some empirical relations were derived for engineering applications.

Additive manufacturing of miniature marine structures for crashworthiness verification: Scaling technique and experimental tests

Undoubtedly, the main advantage of the additive manufacture technology is to allow building miniature structural parts with a large degree of complexity such as to replicate structural details of real-scale marine structures. This work presents a new technique for reproducing the structural response of large-scale thin-walled metallic structures when subjected to crushing loadings by using scaled-down additive manufactured models. This technique couples scaling laws for strain rate sensitive materials and a thickness distortion technique based on the structural collapse mode. In order to validate this coupled technique, the structural response of a large-scale crushing test of a web girder structure was experimentally replicated by using a 1/40 scale reduction model. The results and conclusions summarize the prospects and limitations of additive manufacturing of miniature complex marine structures for structural purposes and crashworthiness verification.