Varying Strain Rates Research Articles

Flow Stress Behavior and Microstructural Evolution of Al 6351 under Varying Strain Rates and Temperatures

Flow Stress Behavior and Microstructural Evolution of Al 6351 under Varying Strain Rates and Temperatures

Deformation Behavior of CrMnFeCoNi High-Entropy Alloy with Heterogeneous Structure at Varying Strain Rates

Deformation Behavior of CrMnFeCoNi High-Entropy Alloy with Heterogeneous Structure at Varying Strain Rates

Interrelation between mechanical and electromagnetic radiation emission parameters with variable notch-width ratios under tensile fracture in silicon steel

Abstract The research investigates the effect of variable notch-width ratios on mechanical and electromagnetic radiation (EMR) parameters during the tensile fracture of silicon steel. The primary purpose is to comprehend the plastic deformation and crack propagation at an atomic level. The mechanical and EMR parameters chosen for analysis were correlated. The EMR energy release rate correlated well with the elastic strain energy release rate. The good fit between the EMR parameters and the plastic zone radius is a novel method to determine the crack growth behaviour of metals. A theoretical model of dislocation predicted the nature of EMR signals at fracture. A reasonable agreement between cross-slip energy with maximum stress at crack instability, the elastic strain energy release rate, and the EMR energy release rate will help assess the dislocation dynamics of metals. The EMR amplitude was sensitive to varying strain rates.

THE INFLUENCE OF THE STRAIN RATE ON THE VALUE OF FRICTION COEFFICIENT

The Male and Cockroft ring compression test stands as one of the methods utilized to determine the coefficient of friction in forming processes. This approach eliminates the need for force measurement. This study presents the outcomes of the Male and Cockroft ring compression test conducted on Hardox 450 material at varying strain rates, conducted without lubricant. The experiments were carried out using a ZD 40 hydraulic press, CFA-80 pneumatic die hammer and split Hopkinson pressure bar test at the Faculty of Mechanical Engineering of Brno University of Technology. The test results were documented on a calibration diagram, revealing a significant influence of strain rate on the coefficient of friction. Specifically, the findings indicate that as the strain rate increases, the coefficient of friction decreases.

The mechanical behavior and deformation mode of multilayer composite structures based on triply periodic minimal surface elements

In this paper, the mechanical behavior and compression deformation mode of three types of composite multilayer structures based on triply periodic minimal surfaces (TPMS) were conducted through experiments and finite element analysis. The results indicate that the load-displacement curves under varying stain rates manifest a double-platform characteristic for all three structure types. The P-G four-layer structure and P-G six-layer structure have no discernible extrusion of the structural layers during compression, and the entirety of the structure displays an almost regular cubic configuration after compression. Nevertheless, local separation was observed in the extruded portion of the P-H six-layer structure after the structural deformation at higher strain rates. For the other conditions, the structure exhibited a bulge but did not display any local detachment or separation phenomena. During the deformation of the P-H six-layer structure, a dome-shaped region emerges in the first and fifth layers. The “crown” layer displays an inverted bell-shaped failure mode for the first layer structure, exhibiting downward extrusion. In contrast, the fifth layer structure displays an upward extrusion and exhibits a bell-shaped failure mode. The P-H 6-layer structure has the best energy absorption performance under quasistatic compression conditions for the P-G 4-layer, P-G 6-layer and P-H 6-layer structure. However, the energy absorption performance of the identical structure remains largely consistent across varying strain rate conditions.

Study on the Micromechanical Interface Response Behavior of Propellants Based on Nano-Impact Testing

Abstract This study utilizes a nano-impact experimental platform to investigate the stress-strain response of propellant interfaces with two different binders, HTPE and GAP. The mechanical behavior of HTPB-AP and GAP-AP interfaces was examined at the nano-scale under varying strain rates, with experiments conducted at rates up to 100 s−1. These experiments successfully captured the strain rate-dependent mechanical properties of both propellant components and their interfaces. The experimental results align well with the rate-dependent power-law viscoplastic constitutive models developed for HTPE, HTPE/AP, GAP, and GAP/AP interfaces, validating the model’s effectiveness in describing the viscoplastic behavior of these materials and their interfaces. The study demonstrates that interfaces generally exhibit lower stress responses compared to bulk materials. HTPE shows higher initial stress responses and more pronounced strain hardening than GAP.

Dynamic strength criterion of concrete utilizing dynamic coordinates

AbstractThe effects of strain rate on the strength of concrete should be considered when analyzing the dynamic responses of concrete structures subjected to earthquakes or explosions. This paper shows that the effect of strain rate on strength characteristics can be attributed to an increase in cohesion. Notably, the effects of friction, hydrostatic pressure, and intermediate principal stress tend to remain rate‐independent under the appropriate reference system. Consequently, a dynamic coordinate system is established to account for the effects of strain rate on isotropic tensile strength. In this dynamic coordinate system, the strength envelopes for concrete closely resemble those in quasi‐static conditions under varying strain rates, as defined in the unified strength criterion. Using this proposed dynamic strength criterion, this paper explores the dynamic characteristics of different stress paths, including uniaxial, biaxial, and triaxial compression and tension. The predictions, both in terms of tendencies and magnitudes, are consistent with test results. The proposed method enables the extension of most strength criteria to dynamic scenarios by introducing two additional parameters with clear physical interpretations. This advancement enhances the current understanding of dynamic strength characteristics and provides a theoretical foundation for dynamic response analysis.

Effect of strain rates on stress corrosion sensitivity of 7085-T7452 thick-plate friction stir welding joint

The stress corrosion behavior of 7085-T7452 high-strength aluminum alloy base material (BM) and its friction stir welding (FSW) joints under varying strain rates during slow strain rate tensile (SSRT) was investigated. The results show that the stress corrosion sensitivity (ISSRT) of both the BM and FSW joints decreases with the increase of strain rate from 10−7 s−1 to 10−5 s−1. Moreover, the BM demonstrates lower ISSRT than the joints. The cracks in the joints exhibit dendritic paths along grain boundaries, with evidence of crack arrest marking (CAM) at localized areas in 3.5 wt% NaCl solution, suggesting both anodic dissolution and hydrogen-induced cracking simultaneously govern the propagation of stress corrosion cracks. There is the forced more test time in the slower strain rate, and the accumulation of stress corrosion coupling damage accelerates with the time, eventually leading to the greater degradation in the stress corrosion resistance and the higher ISSRT.

Ultrasonic and conventional fatigue behavior, strain rate sensitivity, and structural design methods for wrought and cold spray Al-6061

Cold spray is an additive manufacturing process that accelerates powder particles to supersonic speeds to create repairs and bulk depositions with fine-grained microstructures, high density, and good mechanical properties. Fatigue property measurement for these novel materials is critical for their use in safety-critical components, which can be accelerated with the use of ultrasonic fatigue testing. In this work, ultrasonic (20 kHz) and conventional (20 Hz) fatigue studies were conducted on as-sprayed bulk Al-6061 and conventional wrought Al-6061-T6. Complementary fatigue studies of surface preparation (surface finish and residual stress) and fatigue specimen geometry (round versus flat), as well as hole-drilling residual stress measurements, were undertaken to minimize the influence of these confounding variables. Cold spray Al-6061 exhibits fatigue frequency sensitivity, whereas the wrought material does not. Tensile testing at varied strain rates indicates that a portion of the fatigue frequency effect can be attributed to strain rate sensitivity. Fractographic studies show that crack initiation occurs from unbonded powder particles at the surface at high stress amplitude, and transitions sub-surface at lower stress amplitude. The results of these studies were used to create frequency-corrective models of S-N data and Kitagawa-Takahashi diagrams that can be used to design for fatigue crack initiation and growth resistance.

Strain rate-dependent tension-compression asymmetry in cast Mg-Gd-Y alloy: Insights into slip and twinning mechanisms

Tension-compression asymmetry is a critical concern for magnesium (Mg) alloys, particularly in automotive crash structures. This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at various strain rates. Experimental results indicate symmetric yielding stress under both tension and compression at all strain rates, along with a reduction in the tension-compression asymmetry of ultimate stress and plastic strain as the strain rate increases. This trend arises from an unusual strain rate-dependent tension-compression asymmetry, characterized by strain rate toughening in tension and negligible strain rate effect in compression. The differing behavior is linked to the distinct twinning mechanisms under tension and compression. The suppression of twinning under tension contributes to the positive strain rate dependence of pyramidal slip, whereas the activation of abundant twins during compression means that pyramidal slip is unnecessary to accommodate c-axis strain, leading to the absence of a strain rate effect in compression. Abundant twins nucleate consistently from yielding to 2% strain, but only after basal and prismatic <a> slip have mediated microplasticity, suggesting that these slip systems reduce the nucleation stress for twinning during compression, resulting in a lower activation stress for twinning compared to tension. This study provides new insights into micromechanisms of the tension-compression asymmetry in cast Mg-Gd-Y alloys and offers practical guidance for the application of these materials in critical components that must endure both tension and compression under varying strain rates.

Tailoring strain rate sensitivity and creep behavior of CoCrNi multi-principal-element alloys by aging

While simulations predict that local chemical order in multi-principal-element alloys (MPEAs) renders anomalous dislocation behaviors and thereby varied strain rate sensitivity (SRS) and creep behaviors, the experimental demonstration of such an effect is still under exploration due to the challenges in the manipulation of local chemical order. Here we investigate SRS and creep behavior of CoCrNi MPEAs subjected to long-term aging at various temperatures using nanoindentation. Our results reveal that the SRS and creep resistance of the alloys enhance significantly with increasing aging temperatures, with the SRS notably surpassing that of elemental and solid solution counterparts. In particular, unusual magnitude of creep stress exponent is observed at room temperature and the possible mechanisms are discussed. We suggest that long-term aging could be a straightforward method to tailor the microstructural ordering and mechanical properties of MPEAs, aiming at bridging the gap between simulations and experiments.

Influence of Strain Rate on Barkhausen Noise in Trip Steel.

This paper deals with Barkhausen noise in Trip steel RAK 40/70+Z1000MBO subjected to uniaxial plastic straining under variable strain rates. Barkhausen noise is investigated especially with respect to microstructure alterations expressed in terms of phase composition and dislocation density. The effects of sample heating and the corresponding Taylor-Quinney coefficient are considered as well. Barkhausen noise of the tensile test is measured in situ as well as after unloading of the samples. In this way, the contribution of external and residual stresses on Barkhausen noise can be distinguished in the direction of tensile loading, as well as in the transversal direction. It was found that the in situ-measured Barkhausen noise grows in both directions as a result of tensile stresses and the realignment of domain walls. The post situ-measured Barkhausen noise drops down in the direction of tensile load due to the high opposition of dislocation density at the expense of the growing transversal direction due to the prevailing effect of the realignment of domain walls. The temperature of the sample remarkably grows along with the increasing strain rate which corresponds with the increasing Taylor-Quinney coefficient. However, this effect plays only a minor role, and the density of the lattice imperfection expressed especially in terms of dislocation density prevails.

A novel impact approach based on electromagnetic loading technology: A case study on CFRP/Al riveted structures

To investigate the mechanical response and damage behavior of aircraft fuselage composite structures under out-of-plane impact loads more efficiently and flexibility, this paper proposed a novel impact approach and testing platform based on inductive coils to yield electromagnetic impact force. The influence of system key parameters on the electromagnetic loading waveforms were analyzed using an electromagnetic field finite element model. Single/repeated impact tests on CFRP/aluminium alloy (Al) riveted structures were conducted at different voltages (energies) based on this approach. The results indicate that the electromagnetic impact (EMI) approach exhibits significant advantages in both variable strain rate loading and continuous impact loading scenarios. This device can efficiently achieve multi-point and multiple impact loading. The electromagnetic impact forces with various amplitudes and pulse-widths can be accurately obtained by altering voltage and capacitance values, which can demonstrate the good experimental consistency of such test approach. Besides, with this test method, the load threshold for damage formation can be clearly defined: once the impact force exceeds the damage threshold load, the delamination area of the CFRP laminates expand as the impact energy increases. Note that when the provided out-of-plane impact load is slightly higher than the damage threshold load by changing the voltage, significant delamination damage may suddenly manifest in any one impact event of the repeated impacts.

Impact response of 3D printed cornstalk-inspired structures: The effect of indenter shape on penetration

This paper reports the mechanical response and damage tolerance of 3D-printed cornstalk-inspired structures subjected to impact loading. Specimens were subjected to dynamic indentation tests at multiple impact energies with flat, hemispherical, and conical indenters. The mechanical properties of the base material (ABS) were measured across varying strain rates using a Shimadzu® Universal Testing Machine and a Split Hopkinson Pressure Bar. The effect of geometrical variations of the constituents on energy-absorbing capability was also investigated. Damage characteristics were interrogated through X-ray CT scans and provided detailed failure modes associated with each indenter shapes. Further, finite element simulations provided insights into the penetration mechanisms associated with the different indenter shapes. The results demonstrated that test specimens impacted by flat indenters absorbed ∼25 % less energy than those impacted by hemispherical and conical indenters. Among the various indenters, the conical shape had the highest duration of contact force within the specimen before experiencing failure by matrix cracking and complete perforation.

Experimental characterization of aluminum/polymer/aluminum sandwich structures under various loading rates and temperatures: Establishing a constitutive relationship for LDPE

Composite sandwich structures, for example Alucobond, have appeared as auspicious materials in a diversity of engineering applications due to their lightweight, high strength to weight ratio and thermal insulation properties. Analyzing their mechanical behavior in different loading rates is critical to optimizing their performance. This study inspects the mechanical response of Alucobond sandwich composite structures under dynamic and quasi-static compression loadings. Dynamic compression tests, carried out at high strain rates, and quasi-static compression tests, carried out at lower strain rates and temperatures, were used to predict the behavior of the material under different loading conditions. In addition, the mechanical properties of the low-density polyethylene (LDPE) core layer were characterized under dynamic and quasi-static loading conditions, with varying strain rates and temperatures, leading to the establishment of a constitutive relationship for the LDPE material. The comparative study of Alucobond and LDPE highlights the influence of material composition and loading conditions on the mechanical behavior of the composite sandwich structures.

Two-stage heat dissipation in plastic deformation of metals under ultra-high strain rate deformation

Understanding plastic heating at high strain rates is essential for designing material behavior. We employ molecular dynamics to analyze plastic heating and introduce a refined Taylor-Quinney coefficient (TQC) calculating approach. Our results reveal a two-stage heating behavior in high-strength systems, a relaxation stage characterized by rapid heating, stress relaxation, and increasing TQC, followed by a steady-state stage marked by linear temperature increase, constant stress, and stable TQC. The dislocation movement may behave as a plastic heating converter. During the relaxation stage, defect/dislocation nucleation dominates, leading to an increase in TQC as defect density rises upon yielding. Despite an increasing portion of plastic work being stored in defects, the data suggest that dislocations primarily act as sources of heat. In the steady-state stage, an unusual scenario emerges where defect density decreases as plastic deformation proceeds, yet TQC continues to increase due to the release of stored energy. This phenomenon is potentially explained by the annihilation of dislocation dipoles moving towards each other on the same slip plane. Additionally, TQC remains relatively insensitive to variations in temperature and strain rate over a broad range, challenging prior assumptions and expanding the understanding of plastic heating mechanisms.

Dynamic and quasi-static strength of additively repaired aluminum

Additive manufacturing has the potential to repair high value components, saving significant time and resources; however, the level of reliability and performance of additive repairs is still relatively unknown. In this work, the structure–property and performance of laser wire additive manufacturing repairs in 1100 aluminum are investigated. Two types of intentional damage are inflicted on the samples and subsequently repaired with pulsed laser deposition additive manufacturing. Quasi-static (10−3s−1) and high strain-rate (10−3s−1) mechanical testing is carried out with in situ diagnostics and post-mortem imaging. The results show that while the quasi-static strength and ductility of samples with a repaired region are lower than a pristine sample, the dynamic strength under shock loading is comparable. This work highlights both the potential utility of additive manufacturing for repair purposes, the significant risk of compromised performance of additive parts under specific conditions, and the need to test at varying strain rates to fully characterize material performance.

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 and temperature‐dependent shear fracture mechanism of high‐energy propellant/liner interface zone

AbstractThe shear fracture of the high‐energy propellant/liner interface zone occurs in many application cases of solid rocket motors (SRMs). The shear fracture experiment development is thus a crucial issue. Here we aim to study the shear fracture mechanism of the interface zone under varying strain rates and temperatures. Shear experiments are carried out using self‐made specimens containing prefabricated cracks. Force‐displacement curves, experimental images, and fracture surface topographies are obtained at different strain rates and temperatures. The strain field of the specimen surface is analyzed using the digital image correlation (DIC) method. Additionally, the fracture surface topographies are analyzed using ImageJ software. The results show that the shear mechanical properties of the interface zone are strongly dependent on strain rates and temperatures. Specifically, the shear fracture strength and failure displacement exhibit a decrease with increasing temperature and an increase with increasing strain rate. The DIC analysis shows that the fracture strain of the interface zone typically ranges from 0.4 to 0.6. The analysis of the fracture surface topographies reveals that the shear fracture modes are predominantly mixed fractures, including propellant/liner interface fractures and propellant cohesive fractures. Since the propellant/liner interface is more sensitive to strain rate and the propellant is more sensitive to temperature, the propellant/liner interface fracture ratio increases from 1.99 % to 60.26 % with decreasing strain rate and temperature. The results show that the experimental method can effectively be used to study the shear fracture mechanism of the high‐energy propellant/liner interface zone.

Varying strain rates and elevated temperatures effects on the mechanical properties of AZ31B magnesium alloy

This study investigates the monotonic tensile behavior of magnesium (Mg) alloy AZ31B across a temperature range from ambient (25 °C) to elevated (up to 300 °C) with varying strain rates (SR) (1.5 × 10−2 to 1.5 × 10−4 s−1). Mechanical properties such as ultimate tensile strength ( σu), tensile yield strength ( σy), strain to failure ( εf), plastic anisotropy ( r-value), strain rate sensitivity ( m) and strain hardening exponent ( n) were investigated in this study for these strain rates. As the temperature increased from 25 to 300 °C, the following changes in mechanical properties were observed: the yield strength ( σy) decreased by 84.50%, the ultimate tensile strength ( σu) decreased by 87%, the modulus of elasticity ( E) decreased by 63.0%, and the elongation increased by 72.0%. The reduction factors (RF) were proposed for the above-mentioned mechanical properties for varying temperature ranges. The impact of varying temperatures and strain rates on fracture surfaces was investigated using field emission scanning electron microscopy (FE-SEM). The results revealed the presence of tenacity nets, cleavage patterns, and an increasing number of dimples as temperatures increased.