PP/PA/TPEg共混高聚物材料动态力学性能的研究

本文用霍布金生压杆装置（简称SHPB）试验技术研究了两种不同配比的PP/PA／TPEg共混高聚物材料在高应变率（10^2-10^3s^-1）下的动态力学行为。实验表明，准静态下的应力一应变曲线与高应变率下的有较大差别，其动态的杨氏模量、屈服应变随应变率的增大而增大，PP／PA共混材料是一种应变率敏感的高聚物材料。     

Energy consumption in rock fragmentation at intermediate strain rate

In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s⁻¹. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity. Foundation item: Projects(50674107, 10472134, 50490274) supported by the National Natural Science Foundation of China     

Sensitivity Analysis, Determination and Optimization of Granite RHT Parameters

The RHT model has 34 parameters, among which 19 parameters can be obtained by experiments or theoretical calculations and the remaining 15 parameters are difficult to acquire. In this study, firstly, 10 Hopkinson impact tests were conducted to acquire the typical stress-strain curves of granite under dynamic loads. Through the sensitivity analysis, it is found that 13 of the 15 difficult-acquired parameters are effective to affect the shape of the stress-strain curve, and the other two parameters have no effect. Following the initial determination of model parameters with reference to the concrete RHT model, a new approach is proposed to optimize the 13 influential parameters through the LS-DYNA numerical simulation and orthogonal experiments. Finally, the determined granite RHT model parameters are verified by the results of Hopkinson impact tests conducted in this study and the bullet penetration test by Wang et al. Both results of the numerical simulations are in a good agreement with the tested results, which validates the suitability of the proposed method to acquire RHT model parameters for granite and the other rocks.     

Perforation of sandwich plates with graded hollow sphere cores under impact loading

In this paper, sandwich plates made from 0.8 mm 2024 T3 aluminium alloy skin sheets and graded polymeric hollow sphere cores (having various density gradients) are studied. The experiments at 45 m/s were performed with an inversed perforation setup using SHPB system. Quasi-static tests using the same clamping system allow for the rate effect investigation. Numerical simulations are performed in order to get the indispensable local information (which is not experimentally available) to better understand the perforation process.     

Dynamic behavior of ring systems subjected to pulse loading

The paper presents an experimental and numerical investigation into the dynamic behavior of one-dimensional ring systems subjected to pulse loading. The experiments on stress wave propagation in ring systems were performed using a modified split Hopkinson pressure bar test system. LS-DYNA computer code is taken as the calculation platform for numerical simulations of the test system. The numerical results are shown in a reasonable agreement with the experimental results. The characteristics of the stress wave propagated within a single ring and across a chain of rings are discussed. Moreover, the features of distribution of elastic deformation energy in ring systems with respect to various parameters are also demonstrated.     

Effect of specimen size on energy dissipation characteristics of red sandstone under high strain rate简

In this experiment, red sandstone specimens, having slenderness ratios of 0.5, 0.7, 0.9 and 1.1 respectively, were subjected to blow tests using a Split Hopkinson Pressure Bar (SHPB) system at a pressure of 0.4 atmospheres. In this paper, we have analyzed the effect of slenderness ratio on the mechanical properties and energy dissipation characteristics of red sandstone under high strain rates. The processes of compaction, elastic deformation and stress softening deformation of specimens contract with an increase in slenderness ratio, whilst the nonlinear deformation process extends correspondingly. In addition, degrees of damage of specimens reduced gradually and the type of destruction showed a transformation trend from stretching failure towards shear failure when the slenderness ratio increased. A model of dynamic damage evolution in red sandstone was established and the parameters of the constitutive model at different ratios of length to diameter were determined. By comparison with the experimental curve, the accuracy of the model, which could reflect the stress–strain dynamic characteristics of red sandstone, was verified. From the view of energy dissipation, an increase in slenderness ratio of a specimen decreased the proportion of energy dissipation and caused a gradual fall in the capability of energy dissipation during the specimen failure process. To some extent, the study indicated the effects of slenderness ratios on the mechanical properties and energy dissipation characteristics of red sandstone under the high strain rate, which provides valuable references to related engineering designs and academic researches.     

Perforation of aluminium foam core sandwich panels under impact loading—An experimental study

This paper reports an original inverse perforation tests on foam core sandwich panels under impact loading. The key point is the use of an instrumented Hopkinson pressure bar as a perforator and at the same time a measuring device. It aims at a high quality piercing force record during the whole perforation process, which is a weak point of common free-flying projectile-target testing schemes.     

改性聚四氟乙烯材料的力学性能实验研究

为了研究改性低密度聚四氟乙烯材料的力学性能,利用万能试验机进行了准静态拉伸和压缩试验,通过霍普金森杆实验研究其在冲击载荷作用下的动态力学特性.对不同长径比改性与非改性试样在不同载荷加载下的力学特性以及不同冲击速度下的动态响应特性进行了分析.结果表明,通过在聚四氟乙烯材料中添加铜粉可以提高其抗拉强度,改善伸长率,增强抗压缩强度;随应变率的增大,改性聚四氟乙烯的屈服强度得到提高.     

Experimental and numerical investigation on the mechanical responses and cracking mechanism of 3D confined single-flawed rocks under dynamic loading

Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is ...     

High Strain Rate Compressive Tests on Wood

Abstract: The penetrating split Hopkinson pressure bar was used to study the response of dry maple wood under high strain rate impact load. Using longer bar and shorter specimens utilised the assumption of one‐dimensional stress waves travelling along the bars and specimen because the experiment fulfilled the ratio of diameter to length of bars condition in Kolsky bar experiments. The stress–strain relationships and behaviour of the fibre structure materials’ failure were investigated during the compressive dynamic tests at strain rates between 950¹ and 2000 s^?1. The mechanics of dynamic failure was studied and it was confirmed that deformation of specimen is a linear function of energy absorption by specimens.