Papers by Keyword: Strain Rate

Abstract: Fiber-reinforced polymers (FRP) bars have gained widespread recognition as a viable alternative to steel reinforcement in concrete structures over the past decades due to their advantages in corrosion resistance, durability, and lightweight properties. However, existing research and current design codes do not adequately address the dynamic compressive response of FRP bars under high-impact loading conditions. This gap in knowledge presents a significant challenge in accurately predicting the response of FRP-reinforced structures under extreme loading events. Therefore, it is essential to investigate the response of FRP bars under dynamic loading conditions across a range of strain rates to improve design codes and ensure the reliability and safety of structures subjected to such conditions. This study presents an experimental program conducted on basalt FRP (BFRP) bars subjected to dynamic testing using the Split Hopkinson Pressure Bar (SHPB) apparatus. The 12-mm BFRP bars are subjected to impact loading at high strain rates ranging from 345 to 1300 s^-1. These varying strain rates are achieved by adjusting the pressure of the impact bar. A high-speed camera is employed to capture the failure mechanisms and provide visualization of the deformations during loading. The study focuses on evaluating the stress-strain relationship and failure modes of the tested BFRP bars under various loading rates. The results revealed that at higher strain rates of ∼1300 s^-1, BFRP bars lost 40% of its compressive strength when compared to its quasi-static strength (tested at 3.5 x 10^-4 s^-1). At lower strain rates (∼345 s^-1), 20% of the quasi-static strength is lost. At intermediate strain rates (∼590-740 s^-1), one sample showed a strength reduction of 26%, while another sample showed a strength gain of 10%. This proves that BFRP bars are highly strain-rate dependent. Additionally, the results show relatively significant variation in the behavior of the samples at similar strain rates, indicating microstructural differences between them.

Abstract: External conditions such as strain rate and temperature influence the mechanical properties of materials. In this paper, the influence of strain rate on the tensile properties of an additive-manufactured polylactic acid (CR-Wood PLA) polymer is studied experimentally. The key mechanical properties, including tensile modulus, yield strength, and strain at fracture of the material are studied at the low (0.0091/s and 0.91/s) and the intermediate (1/s – 3.63/s) strain rate ranges. The experimental investigation revealed that the stress-strain relationship of the material is influenced by the strain rate, however, differently across the ranges. The yield strength improved with the increase in the strain rate until ἐ = 1.81⁄s. A further increment in strain rate slightly declined the yield strength. The tensile modulus showed a notable decrement, however, only near the transition between the low and intermediate ranges. On the other hand, the strain at fracture monotonically decreased with the strain rate at both ranges. The material underwent significant post-yield plasticity, and a stress whitening throughout the reduced section of the specimens during the low strain rate tests. At higher strain rates, the plasticity was limited, and the stress whitening was localized just at the fracture surfaces.

Abstract: The article is devoted to the determination of the main physical and mechanical characteristics of compressed concrete at different strain rates of its. A method for predicting the main strength and deformation characteristics of compressed concrete in the widest range of its loading rates is proposed: from instantaneous dynamic to long-term with the maximum possible development of creep deformations. This method is based on the well-known law of conservation of potential energy of material deformation (up to its destruction) and the general patterns of change of the known integral characteristic of concrete - the factor of elasticity-plasticity. The functional interdependence of the levels of strength and deformability of compressed concrete for its different strain rates was established.

Abstract: This article is devoted to the modeling of the stress-strain diagram of compressed concrete under the action of dynamic loads of various intensities. The main attention is paid to the influence of the strain rate of concrete on the determining parameters of this diagram. The degree of dependence of the dynamic increase factor (DIF) and the level of critical deformability of compressed concrete both on the rate of its deformation and on the level of elastic-plasticity (class) has been established. The analytical relationship between the main static and dynamic characteristics of the deformation diagrams of compressed concrete is established using the hypothesis of invariance and independence from the load mode of the specific potential energy of the ultimate deformation (destruction) of the material.

Abstract: The tensile behavior of an injection mold glass fiber reinforced polyamide matrix composite was determined between 10^-6-10^-1 s^-1 strain rates at 25, 65 and 90°C for the loading axis 0^o, 30^o and 90^o to the fiber plane. Microscopic studies were conducted to identify typical fracture mechanism involved at different temperatures. The composite exhibited the highest flow stress and elastic moduli sensitivities on the strain rate in the 0^o specimens, followed by the 30^o and 90^o specimens. The highest rate sensitivity was detected in the specimens tested at 25°C and the rate sensitivity declined as the test temperature increased from 25°C to 65 and 90°C. The observed rate sensitivity of the composite was ascribed to the rate sensitivity of the matrix while the elevated temperatures enhanced the fiber-matrix bonding.

Abstract: Effect of grain boundary morphology on ductility dip cracking (DDC) sensitivity of nickel base alloy inconel52 deposited metal was researched by welding thermal simulation method and high temperature tensile test. The sample was hold at 1300 °C for 2S ~ 10s and then stretched at its DDC sensitive temperature 1050 °C at different tensile rates. The DDC sensitivity was compared by reduction of area (VoA) of tensile test sample. The results show that straight grain boundary reduces VoA, precipitates in grain boundaries increases VoA, and VoA increases with the increase of tensile rate. Straight grain boundary causes stress concentration and strain localization at the trigeminal grain boundary, curved grain boundary decreases the maximum Mises stress which make more uniform stress distribution. Precipitates on the grain boundary can play a role of locking the grain boundary migration and disperse the strain concentration at the trigeminal grain boundary. The lower the strain rate, the longer the deformation time, which will lead to decrease of dislocation movement rate. The smaller the critical shear stress of grain boundary sliding, the smaller the deformation resistance, and the full progress of dislocation movement and climbing. Effect of strain rate on DDC needs more research.

Abstract: In this paper, aiming at the heat resistance and thermal deformation process of titanium matrix composites 0 vol.%, 2.5.vol.%, 5.vol.%. Thermal simulation experiment of titanium matrix composites with different (TiB+TiC) strengthening phase content. The measurement accuracy of material displacement is 0.01 mm. The compression is 70%, and the strain rate is 0.1 mm/s and 0.01 mm/s respectively. Compression tests at different strain rates and temperatures were carried out. The experimental results show that when the (TiB+TiC) 5vol% titanium composite is deformed at 0.01mm/s low strain rate, the peak stresses corresponding to 25°C, 250°C,350 °C and 500°C are increased to 1096MPa, 835MPa, 646MPa and 416MPa respectively. Under the condition of high strain rate of 0.1mm/s, the peak stresses corresponding to 25 °C, 250 °C, 350 °C and 500 °C are increased to 1230 MPa, 896 MPa, 723 MPa and 471 MPa respectively. The deformation law of stress rheological curve is roughly the same, and the high temperature zone has good plastic deformation ability. The titanium matrix composite has high compression rheological mechanical properties and good high-temperature plastic deformation ability. It is the preferred material component for the preparation of titanium matrix composite and powder forging.

Abstract: On the worldwide tendency of wight reduction of automobile, aluminum is drawing a large number of researcher’s sights because it’s advantages of low weight, corrosion resistance, flexible and so on. Aimed at understanding high-temperature flow behavior of aluminum alloy A5005, tensile tests were conducted at temperatures 360°C, 430°C, 500°C and strain rates 0.0003s^-1, 0.003s^-1, 0.03s^-1 respectively. For constitutive equation molding, a simplified Johnson-Cook model was adopted to describe high-temperature relationship of A5005 alloy. One of superiorities of this model is the flow stress model can be established more efficiently. What’s more, adiabatic temperature rise is eliminated by introducing development trend of material stress and strain in this model. Finally, the root mean square error (RMSE) was used to check the accuracy of the final model. The results show that the model accuracy increase by temperature increasing and strain rate decreasing, and the simplified Johnson-Cook model can describe stress-strain tendency without losing much accuracy.

Abstract: Titanium alloys are widely used in aerospace and automotive industries due to their excellent mechanical properties, however, the formability is limited, which is an issue during forming. In the present study, the effect of temperature and strain rate on the tensile properties of the titanium α-alloy KS1.2ASN was investigated. It was observed that there is initially no gain in ductility with increase in temperature until 400 °C, however, maximum formability is reached at maximum tested temperature of 600 °C. EBSD analysis revealed that twinning is the main deformation mechanism at room temperature, however, sliding deformation becomes more pronounced with increasing temperature. An increase in strain rate leads to a decrease in elongation, but the influence is less pronounced compared to temperature.

Abstract: The forming limit diagram (FLD) is a widely used tool to assess the formability of a metal sheet [1]. The current study aims to investigate the influence of strain rate, material anisotropy and hardening on the FLD of Ti-6Al-4V predicted by the well-known Marciniak-Kuczynski (M-K) method. The tensile data of quasi-static (8 10^-5 s^-1), intermediate (0.5 s^-1) and dynamic experiments (approximately 1000 s^-1) on Ti-6Al-4V sheet are available at three different orientations, with respect to the rolling direction: 0°, 45° and 90°. Different hardening models are taken into account. Also, von Mises and Hill yield criterion are considered. The results show that the influence of the hardening law on FLD is significant. In particular, the most conservative limit strains are predicted by the Voce law because of its saturation characteristic. The yield criterion is found to only affect the right part of the FLD. Regarding the strain rate influence, the left part of the FLD is mainly dominated by the amount of uniform elongation, while the right part is strongly dependent on the yield function used. Therefore, for this region the effects of strain rate and yield function are difficult to distinguish. Finally, the effect of material anisotropy on the FLD is significant. Under quasi-static conditions, the Lankford coefficient seems to be the driving factor in uniaxial and equibiaxial deformation. However, in plane strain conditions the effect of the strain hardening exponent is dominant.