【作者】 朱德智；

【导师】 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 博士

【摘要】 本文以舱外航天服等微型航天器空间碎片防护为背景,设计并制备了2D-fibers/5A06和TiB2/2024复合材料及其复合结构。利用二级轻气炮、分离式霍普金森压杆(SHPB)、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和高分辨电镜(HREM)等多种手段系统地研究了复合材料薄靶在2.5km/s速度下,粒子直径为0.8~2.0mm撞击时的抗高速撞击能力、靶板宏观损伤特征及其微观组织演变规律,并提出了复合结构材料的设计思路。在高速撞击作用下,2D-fibers/5A06复合材料薄靶的宏观损伤由粒子侵彻穿深和背面崩落构成。(2D-Tif)/5A06复合材料靶板破坏以侵彻穿深为主,背面产生了带裂纹的鼓包或发生略微崩落;(2D-M40f)/5A06复合材料以背面崩落损伤为主,且随着粒子直径的增加崩落损伤区的直径不断增大。(2D-Tif)/5A06复合材料在绝热温升影响作用下弹坑区域组织发生了相变,复合材料界面的TiAl扩散层形成TiAl非晶层及非晶-微晶-多晶-β-Ti的过渡带。高强韧Ti纤维的加入起到了承载和吸能作用,有效减缓了基体合金的变形,抑制了绝热剪切带的形成。(2D-M40f)/5A06复合材料在高速粒子撞击作用下在M40纤维内部形成了大量裂纹,其片层状结构受到损伤。因M40纤维和基体合金二者之间的变形失配和低的层间结合强度,在压缩波和反射拉伸波的作用下,复合材料表现出分层损伤和崩落破坏。两种复合材料的基体合金在高速粒子撞击下被严重挤压变形,形成高密度的位错以及非晶和微晶。在远离弹坑部位,基体合金变形减小,缺陷以微裂纹和微孔洞为主。TiB2/2024复合材料薄靶的主要损伤特征为背面崩落。随着增强相含量的增加,TiB2/2024复合材料抗粒子侵彻穿深能力提高,使得靶板正面坑宽和坑深尺寸不断减小;同时也导致了复合材料抗崩落能力的下降,使得背面崩落损伤区直径不断增加。在分离式Hopkinson压杆压缩时(应变率:1×103~2×103s-1),TiB2/2024复合材料的流变应力随着应变率的增加呈现先增大后减小的趋势。在高应变率压缩过程中,复合材料剪切面上形成绝热剪切带,表现为熔融铝相变带,其形成机理与塑性变形局域化有关。铝基复合材料中绝热剪切带的演变规律为:随着增强相含量和应变率敏感性增加,逐渐由形变带向相变带转变。TiB2/2024复合材料表现出混合断裂特征,包括颗粒的断裂和铝合金基体软化/熔化。随着应变率的增加,复合材料逐渐由脆性断裂失稳破坏发展为流变应力软化诱发的动态失稳破坏。复合材料的抗撞击能力与纤维的强塑性相关,同时还与增强相的连续性相关。高强韧Ti纤维的加入有助于提高基体合金的抗撞击能力,而高模量M40纤维的加入却降低了基体合金的抗撞击能力。本文提出采用平均吸能性能来评价不同破坏特征的复合材料的抗高速撞击能力,在2.5km/s条件下,几种复合材料的抗高速撞击能力高低顺序为: (2D-Tif)/5A06、TiB2/2024、5A06、(2D-M40f)/5A06。本文提出了复合结构的设计思路,即高低阻抗材料层叠排布且低阻抗材料置于靶板后部的结构,并进行了初步的实验验证。结果表明几种复合结构的抗高速撞击能力优于相应的复合材料,其防护性能高低顺序依次为(TiB2/2024+Al)结构、((2D-M40f)/5A06+Al)结构、((2D-M40f+2D-Tif)/5A06)结构。更多还原

【Abstract】 Based on the backgroud of the debris protection materials used for mini-aircraft as space suit, two types of composites as 2D-fibers/5A06 and TiB2/2024 were designed and fabricated by pressure infiltration method. Among these, continuous fibers as Ti fibers and M40 graphite fibers are contained in 2D meshes(fabric), respectively. The impact resistance ability, macro-damage characteristic and microstructure evolution principle of the two types of composites were researched by two-stage light gas gun (at a velocity of 2.5km/s), split Hopkinson pressure bar (SHPB), optical microscope (OM), scanning electron microscope(SEM), transmission electron microscope (TEM) and high-resolution electron microscopy (HREM). Finally, the design idea as novel composite structure was proposed.Results showed that the failure characteristics of 2D-fibers/5A06 composite targets were comprised of the penetration and the spalling on the back surfaces. With the projectile diameter increasing, bulge with cross-cracks or spalling were found on the (2D-Tif)/5A06 composite target. The (2D-M40f)/5A06 composite targets were damaged by delaminating predominantly.Due to the local high temperature generated by high speed projectiles, phase transition happened in the bottom of the crater of (2D-Tif)/5A06 composite target. The TiAl diffusion layer on the interfaces of the composites changed as the TiAl amorphous layer. Moreover, a transition band containing amorphous, micro-crystal, crystal andβ-Ti were found. Analysis showed that adiabatic shear band inner the alloy matrix was restrained obviously by the addition of Ti fibers.Under the impact of high speed projectiles, micro-cracks were formed on the M40 graphite fibers inner the (2D-M40f)/5A06 composites targets. Due to the deformation dismatch between M40 fibers and matrix alloy as well as low layer bonding strength, delamination and spalling occurred on the back of the target caused by compressive waves and tensile waves. The aluminum alloy matrix within the 2D-fibers/5A06 composites were squeezed and deformed seriously near the crater. Dislocations and micro-crystal as well as amorphous were also formed in aluminum alloy matrix under impact. The deformation degree of aluminum alloy matrix reduced far away from the crater, and the defects as micro-cracks and holes were dominated in the matrix.The TiB2/2024 composites showed good penetration resistance and significant spalling damage. With TiB2 particle content increasing, the penetration depth decreased and the diameter of spalling area on the back surface increased.With the content of TiB2 increasing, the flow stress of the composites exhibited rise/fall tendency, which was similar to the values calculated by Johnson-Cook model. And the specimens failed from 45oshearing to split as the TiB2 content over 60%.Adiabatic shear bands as melted aluminum bands were found on TiB2/2024 composite, which was ascribed to the plastic deformation localization. Dislocations as well as the micro-cracks were formed inner TiB2 particls under high speed impact. Aluminum alloy matrix was softened and melted caused by local adiabatic thermal temperature. The TiB2/2024 composites acted as a hybrid fracture mode including the particle cracking and the softening of alloy matrix. With the strain rate increasing, the dynamic failure mechanism was changed from brittle fracture to thermal softening instability.The impact resistance ability of composites was related to the strength/ ductility of fiber reinforcement, also with the continuity of the reinforcement. The addition of Ti fibers with high strength/toughness can improve the impact resistance ability of the alloy matrix, while the addition of M40 fibers with high modulus can not get a goog value. In present work, the mean energy absorption ability was adopted to evaluating the protection capacity for different composites targets. The order of protection capacity against high speed impact for these composites was (2D-Tif)/5A06, TiB2/2024, 5A06 and (2D-M40f)/5A06. Based on the analysis of several composites, we proposed a new design idea about composite structure containing high and low impact resistance materials. Results showed that the propection capacity of the composite structures was better than those of the composites. The propection capacity order for composites structures was (TiB2/2024+Al), ((2D-M40f)/5A06+Al) and ((2D-M40f+2D-Tif)/5A06).更多还原