红外卫星对通用高超滑翔导弹的可探测性分析

随着临近空间高超声速技术的迅猛发展和临近空间高超声速导弹的装备使用,新的军事威胁已成为现实。由于临近空间高超声速导弹飞行弹道低且具有机动飞行的特点,需要对它进行实时探测跟踪才有可能对其飞行弹道进行预测。受地球曲率等因素的影响,地面雷达系统对临近空间高超声速导弹的探测距离有限,且组网探测对雷达数量需求庞大,因此卫星探测是一种较好的手段。对美国当前大力发展的海陆军通用型高超声速滑翔体(Common Hypersonic Glide Body, C-HGB)的红外辐射特性进行了初步分析,并结合高轨红外预警卫星的探测能力,初步分析了预警卫星对处于滑翔飞行阶段的C-HGB的可探测性。结果表明,当前的高轨红外预警卫星难以实现对处于滑翔段的C-HGB的探测,所以需要改进卫星红外探测系统或者组建低轨卫星星座。     

Experimental and numerical investigation on the deformation and failure behavior in the Taylor test

The present paper presents an experimental and numerical study concerning the deformation and failure behavior in the Taylor impact test. Projectiles manufactured from a commercial high strength and super-hard aluminum alloy 7A04-T6 with a nominal diameter of 12.6 mm and a length of 50.8 mm were fired against a hardened tool steel plate by a one- and two-stage compressed gas gun within the velocity range of 175–370 m/s. Three different deformation and failure modes were observed from the test: mushrooming, shear cracking and fragmentation. Individual velocity ranges and the transitions between the deformation/failure modes are identified by both experiments and numerical simulations. Slightly modified Johnson–Cook models of strength and accumulative damage failure are employed in 3D numerical simulations to describe material behavior of the striking cylinders. Good agreement between the numerical simulations and the experimental results was found. Detailed computational results of each scenario are offered to understand the deformation and failure mechanisms.     

Determination of an empirical model for the prediction of penetration hole diameter in thin plates from hypervelocity impact

The purpose of this work is to identify an empirical relationship that describes the size of the hole created in a thin plate from a hypervelocity impact in terms of the material properties and geometry of both the projectile and target. A multivariable power series was selected as the form of the mathematical model to develop this empirical relationship. Material properties and geometry of both the projectile and target were selected as the independent variables of this model to predict the hole diameters in targets. Comparison with historical equations reveals that these new models are more accurate predictors of target hole diameters. This statement is based on a one-to-one comparison of the equations using both the data utilized in developing the new models and “new”, independent data.     

A high strength alumina-silicon carbide-boron carbide triplex ceramic

A ceramic particulate composite composed of oxide, and carbide ceramics was found to have high strength, hardness, and fracture toughness values. A composition consisting of Al₂O₃ with 15 vol% SiC and 15 vol% B₄C additions was produced by hot-pressing at 1650 °C for 30 min, with full density reached after ~5 min at temperature. Both WB and WB₂ were observed, with the W source presumably an impurity from WC milling media, and Al₁₈B₄O₃₃ was also detected following densification. Strength was ~880 MPa, which is greater than values reported for comparable composites of Al₂O₃ containing 30 vol% SiC or B₄C. Vickers hardness was ~21 GPa, and fracture toughness was ~4.5 MPa m^½, comparable to values reported for the binary mixtures. The calculated critical flaw size of the material was similar to the size of the SiC/B₄C clusters and microcracking at grain boundaries. The latter resulting from thermal expansion mismatch between the Al₂O₃ matrix and SiC/B₄C reinforcing phases.     

Preshock-induced phase transition in spalled U–0.75 wt% Ti

Uranium–0.75 wt% Ti samples were spalled in the range of 5–24 GPa shock pressure. One sample was preshocked to a pressure of 24 GPa, `soft' recovered, and then reloaded and spalled at 10 GPa. The spall strength of U–3/4 wt% Ti was found to range from −4.1 to −2.9 GPa when the Romanchenko correction is used in the spall strength calculation. The spall morphology of the sample that was preshocked and then spalled showed a significant change in microstructure from a parent alpha' martensite to a 2-phase eutectoid. The thermodynamically calculated temperature rise resulting from the preshock at 15–24 GPa in these samples is ∼555°C. This temperature is not sufficient to induce such a phase change. However, the preshock conditions additionally increase the flow stress of the U–34 wt% Ti, and it is postulated that this additional hardening is sufficient to increase the temperature above 885°C due to the increased amount of plastic work required during spall, thereby triggering the phase change.     

高强度水下爆炸等效冲击波加载特性研究

为了实现实验室范围内的高强度水下爆炸冲击波加载,在现有非药式水下冲击波加载装置的基础上,对加载水舱的结构进行了改进,并利用实验和仿真相结合的方法对非药式高强度水下爆炸冲击波等效加载特性进行了研究,分析了飞片及活塞的质量对加载冲击波强度和衰减时间常数的影响规律,确定了该方法所产生的高强度水下冲击波加载特性。进而利用该装置对0.5 mm厚铝合金靶板进行了水下冲击波加载实验。实验结果表明,改进后的非药式水下爆炸冲击波等效加载装置能够对目标结构进行有效的高强度水下冲击波加载。     

活性粉末混凝土高温后冲击力学性能研究

摘　要：利用分离式Hopkinson压杆系统,采用铅片作为整形器,分别对常温下、400℃、600℃及800℃高温过火后的RPC试样进行单轴冲击压缩实验。研究高温后钢纤维对RPC材料动态力学性能及吸能特性的影响规律。结果表明,高温过火前后钢纤维对RPC均有增强和增韧的作用。高温后因RPC塑性流动性能的增强,导致钢纤维的增韧作用减弱。RPC动态抗压强度高温后损失的速率高于韧性指标。分析RPC材料冲击压缩过程的能量机制,发现钢纤维提高了RPC的能量吸收率,因此能量吸收能力也得到了增强。利用SEM扫描电镜,从RPC材料微观结构变化的角度分析了其高温后宏观力学性能降低的原因。     

碎片云撞击声发射信号能量特征小波包分析

利用小波包分析技术对碎片云撞击载荷作用下铝合金板声发射信号的能量分布特征进行了研究。首先,介绍了碎片云撞击信号的获取方案及撞击引起的损伤情况;其次,对获取的声发射信号进行小波包分析,得到了信号在频率带上能量分布特征图。最后,讨论了碎片云撞击损伤特征与声发射信号能量分布的关系。分析结果发现,对于相同质量的弹丸,随着其破碎程度的提高,形成的碎片云对后板的损伤程度减少;弹丸具有的初始速度越大,弹丸破碎越完全,碎片云撞击声发射信号中的能量越小;当弹丸破碎程度低时,碎片云撞击引起的声发射信号能量集中在约488kHz以下;弹丸破碎程度越高,信号中488kHz以上的能量所占总能量的比例越大。     

40vol%SiC_P/2024Al复合材料的动态压缩性能

利用分离式霍普金森压杆(SHPB)研究了40%体积分数的SiCP/2024Al复合材料和基体材料2024Al在不同应变率下的动态压缩性能。在高应变率动态压缩时该复合材料与2024Al均表现出应变率不敏感,复合材料屈服应力高于2024Al;与2024Al的应变硬化性能不同,复合材料表现出应变软化性能。利用扫描电镜(SEM)观察动态压缩后复合材料试件的微观组织,发现试件内部出现一些孔洞、微裂纹以及一些增强颗粒的破碎等损伤现象,并且在较高应变率下基体呈现出明显的热软化甚至发生局部熔化,由此判断,在高应变率下SiCP/2024Al复合材料宏观应变软化的机制为内部损伤及基体热软化。将SiCP/2024Al复合材料与2024Al经400℃下烧蚀3 h后自由冷却至室温,利用SHPB再次进行测试,与烧蚀前的测试结果相比,2024Al的性能明显下降,而复合材料的性能变化较小,表现出比基体材料更好的抗高温稳定性能。     

Analysis of debris clouds produced by impact of aluminum spheres with aluminum sheets

Results of two-stage light gas gun testing of two diameters of aluminum spheres impacting 0.5 mm and 1.0 mm thickness aluminum plates were described in this paper. Impact velocities for these tests were between 3.16 km/s and 5.17 km/s. The components of debris cloud and damage patterns in the witness plate were described. The morphologic features of debris clouds such as shape, axial velocity, and diametral velocity were discussed. The size and number of fragments in the internal structure of debris cloud were not evaluated quantitatively, but described qualitatively. As a result, the shape of the leading face of the internal structure of debris cloud appeared to be sensitive to impact velocity, but not t/D ratio (bumper-thickness-to-projectile diameter ratio). The point at which the maximum diameter of the external bubble of debris cloud occurred had a same half spray angle of 30 degree and the last fragments ejected from bumper had a same half spray angle of 42 degree for each test. Fragments after the point mentioned above in the external bubble of debris cloud were ejected as several chains, the number of which is sensitive to impact velocity, but not t/D ratio. The changes in normalized velocity of the measurement points at debris cloud appeared the same trend as conclusions presented by Piekutowski except for the normalized internal structure expanding velocity. A certain value of t/D ratio, at two sides of which, the normalized internal structure expanding velocity appeared different variety trend existed.