关键词:有机玻璃;液压膨胀环实验;高应变率拉伸;碎片尺寸;脆性破碎 Abstract The dynamic fracture and fragmentation of brittle solids under impact loading are important research subjects. However, the experimental study on the tensile fracture and fragmentation of brittle solids is relatively limited. A technique using liquid-driving expansion ring setup was developed for the dynamic tensile fracture and fragmentation testing of brittle materials. This technique was used to study the fragmentation properties of PMMA rings at different expansion velocities. From the observations of the fracture morphology and the residual internal cracks of the recovered fragments, it is concluded that the fracture of the rings is caused by the circumferential tensile stress. The unloading stress waves from the fracture points of the fragments inhibit the further development of other cracks close to the fracture points by unloading the tensile stress in the tension regions. The PMMA ring expansion process was captured using ultrahigh speed camera. The specimen surface expansion velocity was measured using laser interference device DISAR (displacement interferometer system for any reflector). The strain history and fracture strain of ring were captured using the strain gauge on the specimen. Preliminary experimental results conducted on PMMA rings show that: (1) In the range of tensile strain rate , the dynamic failure strain of PMMA is lower than that under the quasi-static tensile loading, which means that PMMA became brittle under higher strain rate loading; (2) Higher loading rates resulted in the more fragments and the smaller size of the PMMA rings; (3) The “non-dimensional fragment size vs. strain rate” data fall between the theoretical fragmentation predictions for ductile material and brittle material.
显示原图|下载原图ZIP|生成PPT 图5应变片发生破坏的情况 . -->Fig.5The strain signals recorded by a strain gage that was broken during the test -->
图6给出了PMMA圆环试件在不同的冲击载荷作用下的周向应变时程曲线. 图6(a)为SHPB子弹发射气压为0.05 MPa时, PMMA圆环试件上记录的应变信号, 此时试件未发生断裂, 整个膨胀环处于弹性振动状态, 周向受到往复的拉压载荷作用, 作为一个结构响应, 整个加卸载时间较长. 显示原图|下载原图ZIP|生成PPT 图6PMMA圆环试件的周向应变时程曲线 ||||(a) 子弹发射气压0.05 MPa, 圆环试件未断裂; (b)子弹发射气压 MPa时, 圆环试件发生断裂. -->Fig.6Circumferential strain profiles of the PMMA rings at different loading levels ||||(a) At 0.05 MPa projectile launch pressure, the PMMA ring was not broken||||(b) At MPa projectile launch pressure, the PMMA rings -->
对PMMA圆环在膨胀过程中产生的全部碎片回收并进行了复原, 如图9所示. 冲击载荷作用越大, 试件经历的拉伸应变率越大, PMMA圆环的碎片尺寸越小. 在较低的子弹发射气压()加载下, 圆环试件受拉伸载荷作用, 碎断成多个碎片; 在较高的弹发射气压(0.4 MPa)加载下, PMMA圆环虽然也碎裂成了多个碎片, 同时也有若干碎片的边角由于复杂的应力波相互作用而进一步破坏形成了更小的碎片. 可在高应变率拉伸载荷(子弹发射气压0.4 MPa以上, 应变率超过400 s)作用下, PMMA圆环碎片的周向长度可能小于横向尺寸. 显示原图|下载原图ZIP|生成PPT 图9典型PMMA圆环碎片的复原图 子弹发射气压 MPa -->Fig.9Fragments of PMMA specimen after the expanding ring tests, projectile launch pressure between MPa. -->
采用不同的子弹发射气压进行实验, 获得了 应变率范围的试件碎片, 图10给出了PMMA圆环的拉伸应变率与回收得到的拉伸碎片个数的关系. 这里, 碎片总数没有统计由于复杂应力状态产生的边角碎片, 断裂应变率通过试件上的应变信号计算而得. 从图10可以看出, 随着拉伸应变率的提高, PMMA圆环在膨胀过程中产生的拉伸碎片个数也增多. 显示原图|下载原图ZIP|生成PPT 图10拉伸应变率和拉伸碎片总数的关系. -->Fig.10The relationship between the tensile strain rate and the total number of the tensile fragments -->
(ZhengYuxuan, HuShisheng, ZhouFenghua.High strain rate tensile fracture process of ductile materials and the influence of material parameters ., 2012, 33(4): 358-369 (in Chinese))
[7]
ZhouF, MolinariJF, RameshKT.Effects of material properties on the fragmentation of brittle materials ., 2006, 139(2): 169-196
[8]
NiordsonFI.A unit for testing materials at high strain rates ., 1965, 5(1): 29-32
[9]
JohnsonPC, SteinBA, DavhRS.Measurement of dynamic plastic flow properties under uniform stress//Symposium on the Dynamic Behavior of Materials: 1963
[10]
汤铁钢, 刘仓理. 一种新型爆炸膨胀环实验装置 . , 2013, 28(2): 247-254
(TangTiegang, LiuCangli.A novel experimental setup for explosively loaded expanding ring test ., 2013, 28(2): 247-254 (in Chinese))
(GuiYulin, SunChengwei, LiQiang, Study on electromagnetic loading technology to realize dynamic tensile of metal ring ., 2006, 26(6): 28-28 (in Chinese))
(WangYonggang, ZhouFenghua.Experimental study on the dynamic tensile fragmentations of <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="Mml45-0459-1879-50-4-820"><mml:mi mathvariant="normal">A</mml:mi><mml:msub><mml:mrow><mml:mi>l</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math></inline-formula> rings under radial expansion ., 2008, 29(3): 245-249 (in Chinese))
(ZhangJia, ZhengYuxuan, ZhouFenghua.Experimental technique for fragmentation of liquid-driven expanding ring ., 2017, 30(2): 35-38 (in Chinese)) [本文引用: 1]
[15]
熊迅等. 石英玻璃圆环高速膨胀碎裂过程的离散元模拟 . , 2018, 50(3):
(XiongXunet al. Discrete element simulation of high velocity expansion and fragmentation process of quartz glass ring ., 2018, 50(3): (in Chinese))
[16]
有机玻璃疲劳和断口图谱编委会 . . 北京: 科学出版社, 1987: 62-65
(Polymethyl Methacrylate Tiredness and Fracture Map Editorial Board . . Beijing: Science Press, 1987: 62-65 (in Chinese))
[17]
ZhouF, MolinariJF, ShioyaT.A rate-dependent cohesive model for simulating dynamic crack propagation in brittle materials ., 2005, 72(9): 1383-1410 [本文引用: 1]
(ZhangZhenya, DuanZhong, ZhouFenghua.Experimental and theoretical investigation on the velocity oscillations of dynamic crack propagating in brittle material tension ,, 2013, 45(5): 729-738 (in Chinese)) [本文引用: 1]