基于平台圆环试样的无机玻璃动态拉伸性能研究

无机玻璃的拉伸强度往往远小于压缩强度,服役过程中玻璃大多会发生拉伸断裂.论文采用平台圆环(flattened circular ring, FCR)试样测试钠钙硅酸盐玻璃的拉伸性能.分别利用电子万能试验机和电磁分离式Hopkinson压杆(electromagnetic split Hopkinson pressure bar, ESHPB)开展准静态、动态单轴单向和单轴双向实验,加载过程中采用高速相机对试样的破坏过程进行观测.结果显示,该材料试样强度具有明显的正加载速率相关性.动态单轴双向加载可比单向加载更快实现应力平衡,但两种应力波加载方式下试样的动态拉伸强度大致相同.高速摄像与动态加载同步分析表明,这是因为试样的裂纹产生时刻与应力峰值时刻几乎同时产生.对三种形式的拉伸实验结果进行对比,发现拉伸强度受试样形状影响,这与试样断裂路径上的拉伸应力分布有关.     

Dynamic Tensile Testing of Soft Materials

Determination of dynamic tensile response of soft materials has been a challenge because of experimental difficulties. Split Hopkinson tension bar (SHTB) is a commonly used device for the characterization of high-rate tensile behavior of engineering materials. However, when the specimen is soft, it is challenging to design the necessary grips, to measure the weak transmitted signals, and for the specimen to achieve dynamic stress equilibrium. In this work, we modified the SHTB on the loading pulse, the equilibrium-monitoring system, and the specimen geometry. The results obtained using this modified device to characterize a soft rubber indicate that the specimen deforms under dynamic stress equilibrium at a nearly constant strain rate. Axial and radial inertia effects commonly encountered in dynamic characterization of soft materials are also minimized.     

一种用于动态拉伸试验装置的新型试件装卡方式

针对杆杆型动态拉伸试验系统设计了一种新型的楔形卡口试件装卡方式.利用ANSYS/LS-DYNA软件,建立采用该新型试件装卡方式的直接式杆杆动态拉伸系统的三维有限元模型,并进行数值仿真试验.得到的波形与SHB(Split Hopkinson Bar)试验典型波形相符合,得到的动态应力应变曲线与输入材料模型曲线趋势是一致的.利用这种装卡方式对一种2024铝合金进行动态拉伸试验,得到的动态拉伸应力应变曲线与利用SHPB试验得到的动态压缩曲线基本一致,证明这种新型试件装卡方式是有效的.     

A Technique for Dynamic Tensile Testing of Human Cervical Spine Ligaments

An experimental study is undertaken to examine the dynamic stress–strain characteristics of ligaments from the human cervical spine (neck). Tests were conducted using a tensile split Hopkinson bar device and the engineering strain rates imposed were of the order of 10²∼10³/s. As ligaments are extremely soft and pliable, specialized test protocols applicable to Hopkinson bar testing were developed to facilitate acquisition of reliable and accurate data. Seven primary ligaments types from the cervical spines of three male cadavers were subjected to mechanical tests. These yielded dynamic stress–strain curves which could be approximated by empirical equations. The dynamic failure stress/load, failure stain/deformation, modulus/stiffness, as well as energy absorption capacity, were obtained for the various ligaments and classified according to their location, the strain rate imposed and the cadaveric source. Compared with static responses, the overall average dynamic stress–strain behavior foreach type of ligament exhibited an elevation in strength but reduced elongation.     

用直径圆盘试验评价小样品塑料粘结炸药拉伸性能的初步研究

在圆盘试验的力学模型基础上 ,测定了JB90 14等七种TATB基PBX的间接拉伸性能 ,为进一步完善该方法做了初步研究。结果显示 :所有PBX均产生中心开裂现象 ,与该模型预测一致 ;同时该测试方法能有效地反映出JB90 14及其经不同改性后得到的三种PBX的整体力学性能变化趋势。这说明圆盘试验方法适用于PBX。通过比较这七种PBX拉伸性能 ,认为JB90 14及其改性的JB90 14 G1应值得注意。     

Dynamic Tensile Response of a Microwave Damaged Granitic Rock

Background

Understanding the dynamic tensile response of microwave damaged rock is of great significance to promote the development of microwave-assisted hard rock breakage technology. However, most of the current research on this issue is limited to static loading conditions, which is inconsistent with the dynamic stress circumstances encountered in real rock-breaking operations.

Objective

The objective of this work is to investigate the effects of microwave irradiation on the dynamic tensile strength, full-field displacement distribution and average fracture energy of a granitic rock.

Methods

The split Hopkinson pressure bar (SHPB) system combined with digital image correlation (DIC) technique is adopted to conduct the experiments. The overload phenomenon, which refers to the strength over-estimation phenomenon in the Brazilian test, is validated using the conventional strain gauge method. Based on the DIC analysis, a new approach for calculating the average fracture energy is proposed.

Results

Experimental results show that both the apparent and true tensile strengths increase with the loading rate while decreasing with the increase of the irradiation duration; and the true tensile strength after overload correction is lower than the apparent strength. Besides, the overload ratio and fracture energy also show the loading rate and irradiation duration dependency.

Conclusions

Our findings prove clearly that microwave irradiation significantly weakens the dynamic tensile properties of granitic rock.

     

大理岩动态拉伸强度及弹性模量的SHPB实验研究

提出了获取脆性材料动态拉伸强度及弹性模量的实验步骤及相关记录数据的分析方法。利用直径为100mm的分离式Hopkinson压杆径向冲击巴西圆盘和平台巴西圆盘试样,测试了大理岩在高应变率加载下的动态力学性能。应力波加载下动态劈裂拉伸圆盘在试样中心产生了约45/s的拉伸应变率。分析了实验的有效性并考虑了试样两个端面应力波波形差异的影响以提高实验结果的精度。结果表明准静态下的公式可适用于动态劈裂拉伸实验;大理岩的动态拉伸强度及弹性模量比静态时有明显的增加。     

基于区间因子法的不确定性桁架结构动力响应分析

研究了不确定性桁架结构的动力响应分析问题.在桁架结构的物理参数、几何尺寸和荷载幅值均为区间变量时,从结构响应的Dulaamel积分式出发,利用区间因子法、区间运算和振型叠加法导出了结构动力响应区间变量的表达式.通过算例考察了结构参数和作用荷载的区间分散性对结构动力响应分散性的影响,经与蒙特卡洛数值模拟结果的比较,表明文中所提出的计算模型和分析方法的合理性和可行性.     

动态拉伸试验中试样应变测试的有效性分析

为了评估将试样通过胶粘连接到加载杆的Hopkinson杆装置所获得试样应变的有效性,对四种强度刚度差异较大的纤维增强复合材料进行了动态拉伸试验。试验时,试样通过环氧胶和杆夹层粘接,试样的应变分别按照Hopkinson杆一维应力波理论计算和试样上应变计直接准确测量得到。结果证明：对小变形碳纤维复合材料,按一维应力波理论计算的应变与试样上直接所测应变值偏差超过100%;对较大变形的GFRP和KFRP层合板,两者偏差小于40%。说明采用Hopkinson杆一维应力波理论计算的试样应变不准确。为修正不准确性,一是通过大量数据分析建立按一维应力波理论计算值与直接测量应变之间的关系式,用此式可使此试验装置获得有效的试样应变;二是借助ABAQUS有限元模拟分析得出粘胶层以及试样过渡弧段的变形,用一维应力波理论计算的应变减去此变形,也可获得有效的试样应变。     

Dynamic Necking of Notched Tensile Bars: An Experimental Study

The mechanics of necking inception in dynamically-stretched notched specimens have been investigated. For that task, a systematic experimental campaign of quasi-static and dynamic tensile tests on martensitic steel specimens has been conducted. Samples with and without notches have been considered. Unlike the quasi-static tests, the dynamically-tested notched samples revealed that, under certain loading conditions, flow localization may develop away from the groove. The experimental results presented in this investigation show that the presence of sharp geometrical imperfections in ductile materials subjected to dynamic loading does not necessarily dictate the necking and fracture locus.     

轴向拉伸下氮化钛纳米杆变形机制及力学性能的分子动力学研究

本文使用分子动力学软件包lammps并采用第二近邻改进型嵌入原子法(2NN MEAM)模拟了单晶氮化钛纳米杆的轴向拉伸破坏过程,分析了分别沿[100]、[111]晶向的不同截面尺寸、不同拉伸应变率、不同温度下的氮化钛纳米杆的力学性能,详细描述了氮化钛纳米杆拉伸变形过程。研究发现, 拉伸晶向、截面尺寸、拉伸应变率及温度均会对TiN纳米杆的拉伸变形过程及屈服强度、弹性模量等力学性能产生不同程度的影响。 沿[100]晶向的拉伸,截面尺寸越大,屈服强度越低;而沿[111]晶向,截面尺寸越大,屈服强度越大。应变率越大,屈服强度及屈服应变越大,但对于弹性模量几乎无影响。温度越高,材料的屈服强度、屈服应变及弹性模量越小,断裂应变越大。不同拉伸条件下的氮化钛纳米杆的拉伸过程均包括弹性变形、塑性变形与断裂阶段。[100]晶向的弹性模量都要高于[111]晶向。     

Microstructure and Tensile Mechanical Properties of Anisotropic Rigid Polyurethane Foam

An understanding of the mechanical properties of solid foams facilitates effective use of such materials, which are often deployed in load-bearing applications such as impact absorbers, cushioning and sandwich structures. This study is an experimental investigation that focuses on the deformation response of rigid polyurethane foam to tension. Microstructural features such as the size and geometry of constituent cells and the struts that define the cell edges, as well as their stiffness and tensile strength, are examined. The nature of cell deformation and fracture are identified through microscopy and the associated micromechanics analyzed. Results show that the cells are elongated and thus the foam exhibits anisotropic properties. Flexure of the struts that define the cell edges is the primary mechanism governing deformation and failure. Information on the mechanical, microstructural and deformation characteristics elicited through this investigation will facilitate formulation of idealized cell-based models to account for the mechanical response of rigid polymeric foams.     

三维DIC在GFRP锚杆拉伸力学性能测试中的应用

随着玻璃纤维增强塑料(GFRP)广泛运用于轨道交通及边坡加固中,其力学性能的测试显得尤为重要。基于三维数字图像相关(DIC)方法,研究了三种不同加载速率下GFRP锚杆的拉伸力学性能,分别得到了应力-应变曲线及弹性模量、抗拉强度、最大力总延伸率等参数。实验结果表明,螺旋状变截面锚杆的轴向应变呈非均匀分布,由三维DIC得到的锚杆弹性模量结果一致性优于传统的接触式引伸计方法,GFRP锚杆几乎呈线性分布的应力-应变曲线表明该材料为典型的脆性材料。     

材料非均匀性对泡沫金属拉伸性能的影响

通过对开孔泡沫铝进行拉伸实验,考察了泡沫金属材料的非均匀性对其拉伸性能的影响.首护先,通过分析同一批试件的初始密度,考察了材料的初始非均匀性;其次,重点考察了初始密度对材料破坏特性的影响.分析表明,即使初始密度比较接近的试件,它们的破坏应力和应变也有较大的离散性;对于不同初始密度的试件,破坏强度有随初始密度的增加而变大...     

Re-Examination of Correlation between Hardness and Tensile Properties by Numerical Analysis

Contact, singular-field, and large-deformation numerical analyses were performed to re-examine the correlation between hardness and tensile properties. Materials have single hardness values, but continuous changes in stress-strain diagrams; it is impossible, in principle, to correlate the hardness to one stress-strain value. Therefore, there must exist an application limit, which is discussed in this study. Because discretization error is unavoidable in such analyses, a method for leveling the discretization error regardless of the analysis condition was introduced. Moreover, in order to generalize the analysis results, the stress-strain diagram used for this analysis was considered as a dimensionless expression in arranging the results. From the analytical results, the following conclusions were deduced. The range in which the empirical equation between hardness and tensile strength is applicable depends on only the value of the work hardening exponent. Moreover, for the 0.05–0.2 range of the work hardening exponent for general steel, the prediction of tensile strength from the hardness is possible with 10% error at indenter face angles between 110° and 136° in case of the wedge indentation.     

Flattened Brazilian Disc Method for Determining the Dynamic Tensile Stress-Strain Curve of Low Strength Brittle Solids

An indirect tensile testing method is proposed to measure the full dynamic tensile stress-strain curve of low strength brittle solids. In this method, the flattened-Brazilian disc (FBD) sample is loaded by modified split Hopkinson pressure bars (SHPB) system. Low amplitude dynamic forces were measured with a pair of piezoelectric force transducers embedded in the incident bar and the transmitted bar. The evolution of tensile stress at the center of the disc sample was determined through finite element analyses using the measured stress in SHPB as inputs. In a traditional Brazilian test, a strain gauge is mounted at the center of the specimen to measure the tensile strain, which is difficult to apply for low strength brittle materials. Thus, two types of non-contact methods, the Digital Image Correlation (DIC) technique and the Laser Gap Gauge (LGG), were used to measure the strain. The DIC method was used to monitor the displacement and the strain map of the specimen during the test, from which the strain at the center of the specimen can be obtained. The accuracy of the DIC results was assessed, and the displacement and strain uncertainties of our system were 0.003 mm and 0.003, respectively. LGG was used to monitor the expansion of the disc perpendicular to the loading axis, from which the average tensile strain is deduced. The numerical simulation revealed that the tensile strain at the center of the specimen is proportional to the average tensile strain and that the ratio is not sensitive to the material elastic parameters. The strain measured through LGG was compared with that measured by the DIC method using photos captured with a synchronized high-speed camera. The result of the LGG method was 20 % smaller than that of the DIC process. However, the latter was limited by the number of frames of the high-speed camera. The feasibility of this methodology was demonstrated using a polymer-bonded explosive (PBX).     

铝合金材料AA-6061-T6和AA-6061-OA的动态拉伸力学性能

铝合金材料蜂窝夹层板结构具有在较低体重情况下的高硬度和高抗冲击性能力。近年来许多关于其在低应变率下冲击能量吸收性质的文献纷纷涌现，但是对于其在高应变率下的能量吸收力学性能的研究却非常贫乏。为了更好地研究铝合金材料蜂窝夹层板结构在高应变率下的能量吸收力学性能，其结构组成材料本身的动态力学性能必须首先得到充分研究。本文介绍和总结了铝合金材料AA-6061的两种热处理成品，T6与OA，在室温（24℃）与低温（-170℃）下的动态拉伸力学性能。在本研究中，霍普金生拉伸杆被应用，拉伸应变率为10^3每秒。     

铝合金材料AA-6061-T6和AA-6061-OA的动态拉伸力学性能(英文)

铝合金材料蜂窝夹层板结构具有在较低体重情况下的高硬度和高抗冲击性能力。近年来许多关于其在低应变率下冲击能量吸收性质的文献纷纷涌现,但是对于其在高应变率下的能量吸收力学性能的研究却非常贫乏。为了更好地研究铝合金材料蜂窝夹层板结构在高应变率下的能量吸收力学性能,其结构组成材料本身的动态力学性能必须首先得到充分研究。本文介绍和总结了铝合金材料AA-6061的两种热处理成品,T6与OA,在室温(24℃)与低温( -170℃)下的动态拉伸力学性能。在本研究中,霍普金生拉伸杆被应用,拉伸应变率为103每秒。