HIGH VELOCITY BRITTLENESS AND HIGH VELOCITY DUCTILITY OF STRUCTURAL SOLIDS

1.基于Kawata等人提出的“单杆法”公式，建立了材料高速拉伸动态应力-应变表征系统，该系统能够在1 × 10^4/s的应变速率范围内给出材料完全断裂前的动态拉伸应力-应变图，有效持续时间达到1160微秒，是目前世界上最长的记录.对纯金属、合金、复合材料、聚合物和陶瓷等不同种类的固体材料在10^3/s范围内的全拉伸应力-应变关系数据以及速度脆性和高速延性现象进行了研究.纯金属：（1）从总体上说，所得到的广泛结果很好地支持了Kawata（1978）提出的晶格系统对高速脆性的影响。(2)纯铁在高速下表现出强烈的脆性。这似乎是BCC金属的基本行为。在实际的结构材料中，应抑制该特性。(3)无氧铜的流变应力在10^3/s范围内明显偏离对数应变率比例，表明其变形机制由热激活型向粘滞型转变.在合金、复合材料、聚合物和陶瓷等方面，也取得了许多关于高速脆性和高速塑性的显著成果。以下是一些示例：GFRP具有显著的高速延性，PC在10^3/s范围内吸收能量增加，Pyrex纤维具有高速延性，PET和尼龙12具有极高的高速脆性等。详情请参阅报告全文所载的39篇论文。

1. The system for the characterization of materials in high velocity tension that can give the dynamic tensile stress-strain diagrams up to complete breaking, in the strain rate range up to lx10^4/s was established, basing upon the "one bar method" formulae proposed by Kawata et al. The effective time duration ranges up to 1160 microsecond, the longest record in the world.2. The data on complete tensile stress-strain raletion in 10^3/s range and the phenomena of the velocity brittleness and high velocity ductility were clari-fied for various categories of solids: pure metals, alloys, composites, polymers, and ceramics.3. Pure metals: (1) Generally speaking, obtained wide results support well crystal lattice systems effect on high velocity brittleness proposed by Kawata in 1978. (2) Pure iron show drastic high velocity brittlness. And this seems the fundamental behaviour of BCC metals. This property should be suppressed in practical structural materials. (3) The flow stress of OFHC copper shows clear upper deviation from log strain rate proportionality in 10^3/s range in tension, suggesting the transition of deformation mechanism to visous type from thermal activation type.4. In the categories of alloys, composites, polymers and ceramics, also, many ramarkable results on high velocity brittleness and high velocity ductility were obtained. Some examples are: remarkable high velocity ductility of GFRP, incres-ing of absorbed energy of PC in 10^3/s range, high velocity ductility of Pyrex glas fiber, extreme high velocity brittleness of PET and Nylon 12 etc.5. Details should be referred to the 39 papers published shown in Full Report.