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Dynamic Deformation Mechanism of Bulk Metallic Glass Composite Reinforced Continuous Metallic Fibers

Title
Dynamic Deformation Mechanism of Bulk Metallic Glass Composite Reinforced Continuous Metallic Fibers
Authors
김경수
Date Issued
2014
Publisher
포항공과대학교
Abstract
This study investigated the deformation and fracture of the bulk metallic glass composite on dynamic loading. First study aims at investigating ballistic impact properties of Zr-based amorphous alloy (LM1 alloy) matrix composites reinforced with woven stainless steel or glass continuous fibers. The fiber-reinforced composites with excellent fiber/matrix interfaces were fabricated without pores and misinfiltration by liquid pressing process, and contained 35~41 volume pct of woven continuous fibers homogeneously distributed in the amorphous matrix. The woven-STS-continuous-fiber-reinforced composite consisted of the LM1 alloy layer of 1.0 mm in thickness in the upper region and the fiber-reinforced composite layer in the lower region. The hard LM1 alloy layer absorbed the ballistic impact energy by forming many cracks, and the fiber-reinforced composite layer interrupted the crack propagation and blocked the impact and travelling of the projectile, thereby resulting in the improvement of ballistic performance by about 20 pct over the LM1 alloy. According to the ballistic impact test data of the woven-glass-continuous-fiber-reinforced composite, glass fibers were preferentially fragmented to form a number of cracks, and the amorphous matrix accelerated the fragmentation of glass fibers and the initiation of cracks. Because of the absorption process of ballistic impact energy by forming very large amounts of cracks, fragments, and debris, thus, the glass-fiber-reinforced composite showed the better ballistic performance than the LM1 alloy. Next study, two Zr-based amorphous alloy matrix composites reinforced with STS304 stainless steel continuous fibers whose diameters were 110 μm and 250 μm were fabricated by the liquid pressing process. Using a Hopkinson pressure bar, the compressive deformation behavior was investigated at a strain rate of about 103 sec-1, and the results were then compared with those obtained under quasi-static loading. 65~68 vol pct of STS fibers were homogeneously distributed in the amorphous matrix, in which considerable amounts of dendritic crystalline phases were present. According to the dynamic compressive test results, shear cracks were formed at the maximum shear stress direction in the 110-μm-diameter-fiber-reinforced composite to reach the final failure. In the 250-μm-diameter-fiber-reinforced composite, fibers were not cut by shear cracks because the fiber diameter was large enough to restrict the propagation of shear cracks, while taking over a considerable amount of compressive loads over 1500 MPa. This composite showed the higher yield and maximum compressive strengths and plastic strain than the 110-μm-diameter-fiber-reinforced composite because of the sufficient ductility of STS fibers, the effective interruption of propagation of shear cracks, and the strain hardening of fibers themselves.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001675421
http://oasis.postech.ac.kr/handle/2014.oak/2146
Article Type
Thesis
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