Effect of coral sand powders and seawater salinity on the impact mechanical properties of cemented coral sand

Coral sand is one kind of the important building materials in coral reef engineering practice. The use of cement as a stabilizing agent can significantly improve the mechanical properties of coral sands and is widely applied in the subbase engineering construction in coral reef islands. Cement-stabilized coral sand structures may contain high contents of fine coral particles and salinity because of the high crushability of coral sands and the existence of seawater surrounding them. In this study, the effects of coral sand powders and seawater salinity on the dynamic mechanical properties of cemented coral sand (CCS) were investigated through the split Hopkinson pressure bar (SHPB) tests and Scanning Electron Microscope (SEM) analysis. It was found that the strength (i.e., the peak stress) of CCS specimens increased firstly and then decreased with the increase of powder content. The specimens reached the maximum peak stress when 3% powder content was included. The initial improvement of CCS strength was attributed to the pore-filling effect of coral powders, namely, the micro pores of the CCS specimens could be more effectively filled with higher percentages of coral powders being used in the experiments. However, excessive coral powders resulted in the reduction of specimen strength because these powders could easily be cemented into agglomerates by absorbing water from the specimens. These agglomerates could reduce the cementation strength between the coarse coral particles and the cement. Meanwhile, the peak stress of CCS specimens was found to be negatively correlated with the average strain rate and the ultimate strain. The degree of specimen fracture was found to be correlated with the amount of specific energy absorption during the tests. Furthermore, the “sulfate attack” caused by the inclusion of salinity of water had different influences on the CCS specimens with different coral powder contents. The ettringite and gypsum produced in “sulfate attack” could fill the pores and lead to cracking of the specimens, significantly affecting the specimen strength.     

冲击压缩载荷下蓝宝石的动态力学性能试验方法（下）

文章对目前氧化铝陶瓷动态力学性能的研究现状进行了相关的介绍,同时采用霍普金森压杆技术对单晶α氧化铝（蓝宝石）的动态力学性能进行了简单的试验,得到其应力-应变曲线,蓝宝石是一种硬脆材料,受到冲击压缩载荷的作用,会有一定的塑性;进而对试验数据进行相关处理,得到蓝宝石的弹性模量以及高应变率下蓝宝石的抗压强度和失效应变。     

AZ31镁合金中绝热剪切带的组织演变规律

为了深入了解镁合金绝热剪切带与裂纹的关系,进而揭示镁合金在高速冲击载荷作用下局部变形绝热剪切的组织演变规律,采用分离式Hopkinson压杆对AZ31镁合金的帽状式样进行冲击压缩实验,而后利用光学显微镜,扫描电镜和维氏硬度计分别对冲击后的AZ31试样进行分析。结果表明,绝热剪切带形成于最大剪应力方向,随着冲击载荷的不断增加,沿着切应力方向上的微孔洞和微裂纹不断长大,直至彼此相互连接成裂纹,最终导致材料的断裂。经对剪切带及周围组织维氏硬度的测量发现,剪切带内细小晶粒区的硬度明显高于周围组织。     

芳纶纤维复合材料包裹混凝土短柱轴心动态抗压强度研究

采用空军工程大学的100分离式霍普金森压杆(SHPB)装置,对芳纶纤维材料(AFRP)包裹混凝土短柱在高应变率条件下的抗压强度进行了试验研究。研究结果表明:在高应变率下,采用AFRP加固混凝土短柱,动态抗压强度得到了显著提高,并随应变率上升而增长;相同应变率水平下,动态抗压强度随AFRP加固层数的增加呈现出先增大后减小的特性,其中两层AFRP包裹混凝土短柱增强性能最优。另外,考虑应变率效应,对Bethet强度模型进行修正,得到了适用于高应变率条件下的AFRP包裹混凝土短柱强度模型。     

用SHPB径向冲击边裂纹平台圆环(ECFR)的动态断裂实验

为了研究岩石的Ⅰ型动态断裂韧度测试方法,用大直径(100 mm)分离式霍普金森压杆(SHPB)对边裂纹平台圆环(edge cracked flattened ring,ECFR)砂岩试样进行径向冲击实验。分别用普通应变片和高精度裂纹扩展计2种测试元件监测试样起裂时刻和测定裂纹传播速度,比较了它们的准确性和合理性。用实验-数值结合普适函数分析测定了砂岩的动态起裂韧度和动态扩展韧度,初步探讨了动态加载率影响动态起裂韧度的原因,以及裂纹扩展速度对动态扩展韧度的影响,对ECFR试样裂纹扩展路径弯折现象也进行了理论分析。研究结果表明：裂纹扩展计测定比应变片更为灵敏、准确、合理。加载率在(0.74~4.48)×104 MPa·m1/2/s范围内动态起裂韧度随动态加载率的增大而增大,裂纹扩展速度在(0.24~0.34) cR范围内动态扩展韧度随裂纹扩展速度的增大而提高。     

Dynamic rock tests using split Hopkinson (Kolsky) bar system e A review

Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different fr...     

SMD石英晶体抗高过载性能的研究

为了研究SMD石英晶体的抗高过载能力,采用自由式霍普金森压杆对7050、6035、5032、3225、3225(一级加固)、3225(二级加固)六种型号SMD石英晶体进行高过载环境下的动态加载测试。结果表明,在高过载条件下,SMD石英晶体的抗高过载性能随尺寸减小而不断提高,并且产品经历高过载环境后电气参数的不良率逐步降低。未经过加固处理的各型号SMD石英晶体(7050、6035、5032、3225)经过高过载试验(50 000~80 000 g)后,电气参数均出现超差,不能满足武器系统的要求。经过加固处理的SMD石英晶体样品(3225一级加固、3225二级加固)经过高过载试验可以正常工作。     

一种RDX基PBX炸药力学性能和本构关系研究

利用分离式霍普金森压杆(SHPB)对一种RDX基PBX炸药进行了高应变率加载试验,得到了其在不同应变率(300~1 200 s-1)范围内的力学性能,并用扫描电子显微镜(SEM)对回收样品进行了微观分析。结果表明:材料的力学性能和损伤均具有明显的应变率效应。采用含损伤的ZWT非线性黏弹性本构模型,对试验数据进行了拟合,拟合曲线和试验曲线吻合良好。     

全珊瑚海水混凝土冲击压缩性能试验研究与数值模拟

采用直径为75 mm的霍普金森压杆对强度等级为C30和C50的全珊瑚海水混凝土(CASC)以及剑麻纤维增强全珊瑚海水混凝土(SFCASC)进行了冲击压缩试验,并使用LS-DYNA软件对CASC的冲击性能进行了模拟.结果表明:CASC与SFCASC的动态增强因子DIF与应变率(ε)s、立方体抗压强度fcu有关,建立了 DIF关于(ε)s与fcu的二元函数模型;通过试件的破坏形态分析可知剑麻纤维能够有效增强CASC的抗冲击性能,当应变率为52.4 s-1时,CASC-C50试件破坏较为严重,而SFCASC-C50试件在应变率为56.9 s-1时仍能保持完整的形态,只在边缘处出现少量裂缝;采用LS-DYNA软件对CASC-50的冲击压缩过程进行数值模拟,通过试验数据确定了 HJC模型参数,模拟的动态抗压强度与试验值的误差在1.0％～4.9％,模拟动态临界应变与试验值的误差在 4.3％～18.3％.