Deformation temperature and material constitutive model of cupronickel B10

Cupronickel B10—an important material used in aircraft carriers—exhibits excellent electrochemical and mechanical properties, such as high corrosion resistance and weldability. The Split-Hopkinson pressure bar (SHPB) test is a classical method to obtain the dynamic mechanical properties of solid materials. However, the deformation temperature has long been ignored in SHPB studies, which results in low accuracy of the material constitutive model. Thus, in this study, a new method for obtained the deformation temperature was proposed and the modified material equation was validated using experimental data. Quasi-static compression and SHPB experiments were conducted with a thermocouple. The results revealed that the deformation temperature of the quasi-static tests was nearly zero, whereas that of the SHPB experiments ranged from 40 to 90 °C. Therefore, the method developed to describe the deformation temperature can be used to improve the precision of SHPB experiments, as demonstrated for the case of cupronickel B10.     

Plastic bulging of sheet metals at high strain rates

The biaxial bulge test is a material test for sheet metals to evaluate formability and determine the flow stress diagram. Due to the biaxial state of stress induced in this test, the maximum achievable strain before fracture is much larger than in the uniaxial tensile test. A new dynamic bulge testing technique is simulated and analyzed in this study which can be performed on a conventional split Hopkinson pressure bar (SHPB) system to evaluate the strain-rate dependent strength of material at high impact velocities. Polyurethane rubber as pressure carrying medium is used to bulge the OFHC copper sheet. The use of hyperelastic rubber instead of fluid as a pressure medium makes the bulge test simple and easy to perform. The input bar of SHPB is used to apply and measure the bulging pressure. The finite element simulation using ABAQUS/explicit and analytical analysis are compared and show good correlation with each other. The results clearly show that as the strain-rate increases, the strength of the OFHC copper increases. From the study, a robust method to determine the material behavior under dynamically biaxial deformation conditions has been developed.     

High-temperature dynamic deformation of aluminum alloys using SHPB

This paper investigates the dynamic deformation behavior of two aluminum alloys, 2024-T4 and 6061-T6, using a modified split Hopkinson pressure bar (SHPB) with a pulse shaper technique at both elevated and room temperatures. An experimental strategy is proposed, and the dynamic deformation behaviors of two alloys are evaluated with the modified high-temperature SHPB apparatus. The experiments were carried out under varying strain rates and temperatures. The reflected waves modulated by the pulse shaper, the flow stress-strain relationships, the strain rates, the front- and back-ends stresses during the dynamic deformation period were measured at varying high temperatures. Experimentally obtained data were used to evaluate the parameters in the material constitutive equation, such as the Johnson-Cook (JC) constitutive model.     

SHPB实验技术及其发展

基于材料动态力学性能研究，全面阐述SHPB测试技术的基本原理，以及近年来在测试材料动态力学性能方面的发展及应用。     

考虑成形方向的航空铝合金修正本构模型的构建

为了能够准确地反映材料成形方向对其动态力学性能的影响,利用电子万能试验机及分离式霍普金森压杆（SHPB）装置,对航空铝合金7050-T7451板材沿不同成形方向（法向ND,横向TD,轧向RD）取样,并进行准静态加载试验和动态冲击剪切试验。结果表明：成形方向是影响材料准静态和动态力学性能的重要因素之一,在动态冲击剪切过程中,铝合金7050-T7451表现出一定的应变率敏感性和正应变率强化效应。基于材料的成形方向影响规律,构建包含应变率敏感函数项的修正的Johnson-Cook本构模型,并对比验证修正模型与试验数据的结果,证明了修正的、包含应变率函数项的材料本构模型更适用于描述不同成形方向下的材料动态力学性能,该模型能够为建立精确可靠的各向异性材料仿真模型提供数据支持。     

0Cr18Ni9不锈钢本构模型及其对切削力预测影响分析

利用MTS材料试验机和分离式Hopkinson压杆(SHPB)实验装置对经过1100℃固溶处理后的0Cr18Ni9不锈钢的静态力学性能和动态力学性能进行了测量,用Johnson-Cook模型拟合了材料的本构关系,用正交切削实验识别了Johnson-Cook模型材料参数。将SHPB实验和切削实验两种方法得到的Johnson-Cook材料模型应用于切削力的预测,分析了不同实验方法得到的材料模型在切削力的预测中的适用性,为不锈钢切削研究中的分析模型和数值计算中的材料流动应力模型选择提供参考。     

A dynamic punch method to quantify the dynamic shear strength of brittle solids

Shear strength is an important material parameter for brittle solids. This parameter has been extensively used in material failure models. Although a few methods have been proposed to quantify this parameter under the static loading condition, there is no such a method available to measure it under dynamic loading conditions. This paper presents a punch shear device to measure the dynamic shear strength of brittle solids. In this method, a split Hopkinson pressure bar system (SHPB) is used to exert the dynamic load to a thin disc sample, which is placed in a specially designed holder to minimize the bending stress induced by punching. The sample holder also allows the punch head to load the sample directly and in combination with momentum-trap technique in SHPB, it enables soft recovery of the rock plug and rock ring produced by the punching test. The flexibility and applicability of this method is demonstrated by the application of an isotropic and fine-grained sandstone. Within the theoretical framework of the classical Mohr-Coulomb failure model, the obtained dynamic shear strengths are consistent with the dynamic tensile strengths for the same rock from the literature.     

Dynamic deformation behavior of aluminum alloys under high strain rate compressive/tensile loading

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A16061T-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.     

6063铝合金在冲击载荷下的尺寸效应及数值模拟

采用霍普金森压杆(SHPB)在不同冲击压力下对不同尺寸的6063铝合金圆柱试样进行压缩实验。结果表明：在相同压力冲击下,材料的应变率随着试样高径比和横截面的增大而减小。不同尺寸试样在相同的应变率下得到的应力-应变曲线基本吻合。尺寸(直径×高度)为φ8mm×4mm与φ8mm×5mm的试样能获得较广的应变率响应范围。采用ABAQUS有限元软件对铝合金的SHPB动态冲击实验进行了数值模拟,通过二波法计算得到的应力-应变曲线与拟合结果及实验结果吻合较好。     

Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 10~4–10~6 s~(–1). Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar(SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10~(–4)–10~4s~(–1). The Johnson Cook(JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×10~4 s~(–1)) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests(10~(–4)–10~4 s~(–1)) and simulation(up to 3×10~4 s~(–1)). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.     

CCCD-SHPB动态断裂试验系统原理及数值分析

提出在分离式Hopkinson压杆(split Hopkinson pressure bar,SHPB)上用中心裂纹圆盘(central cracked circular disk,CCCD)型试件形成CCCD-SHPB试验系统来实施脆性材料的动态断裂试验.该系统的基本思想是基于SHPB的一维试验原理,得到中心裂纹圆盘型试件两端载荷的平均载荷;推广准静态的应力强度因子公式,并以此平均载荷代入以获得动态应力强度因子.对此动态断裂试验系统的三维动力学数值分析表明,CCCD-SHPB动态断裂试验方法是有效的,用此动态应力强度因子表征和测试脆性材料动态断裂韧度的方法也是有效可靠的.     

光纤光栅用于低阻抗材料动态性能测试的研究

光纤Bragg光栅用于材料性能测试是一个重要的研究方向。本文介绍了基于分离式霍布金逊压杆(SHPB)的低阻抗材料动态性能测试的原理;探讨了光纤光栅传感器用于SHPB实验装置中应变测试的相关问题;推导了低阻抗弹性杆中传播的应力波σ与光纤光栅传感器的波长漂移量ΔλB之间的关系式;构建了光纤光栅高频动态应变测试系统,对SHPB实验装置中被撞击弹性杆的表面应变进行了测试,并与现有仪器进行了对比;实验结果显示,构建的光纤光栅动态应变测试系统在10KHz的频率范围内,具有40dB的信噪比;研究表明,光纤光栅在低阻抗材料的动态性能测试中具有很好的应用前景。     

A unified analytic and numerical approach to specimen behaviour in the Split-Hopkinson pressure bar

Basic results of a detailed analytical, experimental and numerical study are presented concerning determination of an optimum specimen geometry used in the Split-Hopkinson Pressure Bar (SHPB) test technique. Particular topics treated are the longitudinal and axial specimen inertia and the effects of interfacial friction between the Hopkinson bars and cylindrical specimen. A unified approach to inertia and friction is offered through the consideration of energy balance. The formula for the optimum specimen geometry has been derived and thoroughly analyzed. To demonstrate some features of specimen behaviour with friction effects, 10 height to diameter ratios were examined for aluminium specimens. Quasi-static and dynamic experiments for each specimen geometry were performed. The experimental results were then compared with simple numerical calculations of wave mechanics in the SHPB system, including interface friction and the elastic-plastic response of the specimen. It has been shown that the proper treatment of frictional effects, along with inertia, is crucial for an exact determination of the material response during fast plastic deformation.     

Influence of interfacial friction and specimen configuration in Split Hopkinson Pressure Bar system

Influences of interface friction and specimen configuration on the material dynamic response using split Hopkinson pressure bar (SHPB) experiment are evaluated using nonlinear finite element (FE) analysis. The effect of various friction conditions between specimen and the transmitted/incident bars in SHPB system is investigated for different specimen geometries. Cylindrical and cuboid specimens with one- and four-layered configurations are adopted and the stress states along the specimen are analyzed. Results indicate that the transmitted signal decreases and the reflected signal increases with friction coefficient increasing. Interface friction brings great variation in stress triaxiality and Lode parameters in the SHPB specimen. Experimental tests are also conducted in this study to verify the conclusions made through FE simulations.     

Mechanical characterization at intermediate strain rates for rate effects on an epoxy syntactic foam

An intermediate strain-rate mechanical testing technique was developed through proper modifications of a hydraulically driven loading frame (MTS 810) and a split Hopkinson pressure bar (SHPB). The modified MTS and SHPB were used to obtain valid stress–strain data for an epoxy syntactic foam at intermediate strain rates in the order from 10⁻¹ to 10² s⁻¹. Additionally, lower and higher strain-rate characterization of the foam material was conducted, such that the compressive stress–strain data of the syntactic epoxy foam were obtained at strain rates from 0.005 to 2150 s⁻¹ without any gap in the intermediate strain-rate range. The syntactic epoxy foam exhibited nonlinear strain-rate dependency of failure strength.     

Material flow stress and failure in multiscale machining titanium alloy Ti-6Al-4V

Titanium Ti-6Al-4V alloy is a typical difficult-to-machine material due to its unique physical and mechanical properties. The material properties of Ti-6Al-4V play an important role in process design and optimization. However, the dynamic mechanical behavior is poorly understood and accurate predictive models have yet to be developed. This work focuses on the dynamic mechanical behavior of machining Ti-6Al-4V beyond the range of strains, strain rates, and temperatures in conventional materials testing. The flow stress characteristics of strain hardening and thermal softening can be predicted by the Johnson–Cook model coupled with the adiabatic condition. The predicted flow stresses at small strains agree very well with those from the split Hopkinson pressure bar (SHPB) tests, while the predicted flow stresses at large strains also agree with the calculated flow stresses based on the cutting tests with a suitable depth of cut. Heat fraction and temperature parameter control the range of thermal softening and the decrease rate of flow stress. The material may exhibit super plasticity at a small depth of cut with a large radius of the cutting edge in micromachining. Strain rate is one important factor for material fracture close to the cutting edge. The failure strain increases linearly with the increase of homologous temperature, while it only increases slightly with the strain rate.     

一种栅格形缓冲装置结构设计方法研究

针对一种栅格形缓冲装置的动态冲击工况,采用SHPB(split Hopkinson pressure bar)试验系统对相关材料的动态力学性能进行试验研究,获取相应的动态力学性能参数.采用动边界及动网格技术,建立基于流固耦合的缓冲装置仿真计算模型,并根据能量等效和速度一致的原则开展缓冲装置压溃试验,对仿真计算模型进行修...     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

Dynamic deformation behavior of bovine femur using SHPB

This paper investigates the dynamic deformation behavior of bovine femur using a modified split Hopkinson pressure bar (SHPB) with a pulse shaper technique. The shape of the incident and reflected pulses modulated by the pulse shaper were measured and compared to each other to find a suitable thickness. The experiments were carried out under varying strain rates with a selected thickness for the pulse shaper. The effect of pulse shaper thickness on the rising time, stress-strain relationship, strain rates, and front and back-end stresses during the dynamic deformation period was investigated. Experimentally-obtained data were used to find a bilinear relationship between the failure stresses and the strain rates of bovine femur specimens in both longitudinal and radial directions. The failure strains, however, linearly decreased with increasing strain rates.