Size-dependent failure of the strongest bulk metallic glass
Size-dependent failure of the strongest bulk metallic glass
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最强块状金属玻璃的尺寸依赖性失效
DOI：
10.1016/j.actamat.2019.08.019
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发表时间：
2019
期刊：
影响因子：
9.4
通讯作者：
Volkert Cynthia A.
中科院分区：
文献类型：
--
作者：
Qu Ruitao;Tonnies Dominik;Tian Lin;Liu Zengqian;Zhang Zhefeng;Volkert Cynthia A.
将样品尺寸缩小到微米尺度后，对脆性强的co55ta10b35块体金属玻璃（BMG）进行压缩时，观察到明显的脆性-延性转变，破坏模式从破碎到剪切带的剧烈变化。宏观压缩下的破碎破坏以劈裂开裂为主，与剪切带破坏完全不同，主要来源于夹杂物等外在缺陷。为了揭示剪切带裂开裂的临界条件，对不同微柱试样进行了有意引入孔洞作为外部缺陷的试验，并对破坏时刻的应力分布进行了有限元模拟分析。发现剪切面准则对于估计以剪切带为主的破坏所需的名义应力是相当有效的。但与传统脆性固体不同的是，即使最大拉应力达到临界值，也不会发生脆性劈裂开裂。为了启动劈裂，需要在一个临界距离上有一个高拉应力区域，这取决于BMG的缺陷尺寸和断裂韧性。该方法所证明的剪切破坏和劈裂破坏的临界条件可用于估计各种具有复杂几何形状的BMG部件在大长度尺度下的破坏条件，并可用于基于脆性BMG设计韧性复合材料。作为实例，提出了一种避免多孔BMG材料脆裂断裂的设计准则。
Upon reducing the sample size into micrometer scale, an obvious brittle-to-ductile transition accompanied by a drastic change of failure mode from shattering to shear-banding was observed when compressing the brittle but strong Co55Ta10B35bulk metallic glass (BMG). The shattering failure under macroscopic compression is dominated by splitting cracking, which completely differs from shear-banding and originates from extrinsic defects like inclusions. To reveal the critical conditions for shear-banding and splitting cracking, various micropillar specimens with intentionally introduced holes as extrinsic defects were tested, and the stress distributions at the failure moment were analyzed with finite element simulation. The shear plane criterion was found to be quite effective to estimate the nominal stress required for the failure dominated by shear-banding. However, brittle splitting cracking does not occur although the maximum tensile stress reaches the critical value, which is different from traditional brittle solids. To initiate splitting cracking, a high-tensile-stress region over a critical distance, which depends on defect size and fracture toughness of the BMG, is required. The critical conditions for shear failure and splitting cracking demonstrated in this approach can be used to estimate the failure conditions of various BMG components with complex geometries in a wide range of length scales, and to design tough composites based on brittle BMGs. As an example, a design criterion to avoid brittle splitting fracture of porous BMG materials is proposed.