CFRP层合板冲击后剩余强度及黏弹性能研究

通过对制备的环氧基碳纤维增强复合材料(CFRP)层合板进行低速冲击剩余压缩强度试验研究，分析了CFRP层合板的冲击后剩余性能，然后观察CFRP层合板的冲击凹坑回弹现象，分析CFRP层合板的黏弹性能，深入分析冲击过程中能量的吸收与转化。结果表明：当冲击能量越来越大时，CFRP层合板的损伤越来越严重，其剩余压缩强度越来越低；从凹坑边缘到凹坑中心处，CFRP层合板的应变能密度逐渐增大；凹坑回弹部位位于凹坑中心区域附近，呈现局部突起状，最终凹坑剖面近似于不规则“W”形。     

冲头形状对层合板低能量冲击损伤尺寸及剩余压缩强度的影响

为探索冲头形状对层合板低能量冲击损伤尺寸及剩余压缩强度的影响,采用不同形状的冲头对T700/DS1202层合板进行了低能量冲击试验,测量损伤尺寸及其冲击后的剩余压缩强度。结果表明:随着冲击能量等级的增加,锥形冲头造成的损伤更易向深度方向发展,当损伤深度≥0.315 mm时,层合板背部出现裂纹,造成层合板剩余压缩强度退化到90%以下;同时,冲头形状会影响冲击能量门槛值,锥形冲头与圆形冲头的冲击能量门槛值分别为5 J·mm-1、6.67 J·mm-1。     

复合材料层合板静压痕试验及全过程数值分析

复合材料层合板在静压痕力作用下主要发生层间分层、基体开裂、基体压缩破坏、纤维断裂和纤维压坏这几种损伤模式。本文利用ABAQUS有限元程序,对在静压痕力作用下的复合材料层合板建立一个基于Hashin强度准则的全过程模型,并对各层各单元进行损伤演判。利用有限元模型对碳纤维NCF材料层合板在静压痕力作用下的荷载-位移曲线进行预测,并模拟层合板的损伤全过程,以及预测凹坑深度与静压痕力的关系曲线。对层合板进行静压痕试验,测试复合材料层合板在静压痕力作用下的荷载-位移曲线,并在试验过程中用凹坑深度仪测量层合板的凹坑深度。将数值模拟与试验结果比较,两者结果较为吻合。     

复合材料层合板低速冲击后的力学性能试验研究

对特定铺层的5224/CF3052平纹织物复合材料层合板进行了低速冲击和冲击后拉伸、压缩及弯曲试验。探讨了层合板在冲击试验过程中的损伤过程、特征和机理;分析了凹坑深度对层合板冲击后拉伸、压缩和弯曲强度的影响规律。结果表明:冲击后拉伸、压缩及弯曲强度降幅分别为60.9%、50.4%及28.4%,冲击后拉伸强度降幅最大,应引起注意。与冲击后压缩试验结果类似,凹坑深度与冲击后拉伸、弯曲剩余强度关系曲线存在拐点现象。     

平纹编织复合材料层板高速冲击损伤机理研究

根据碳纤维平纹编织复合材料层板在高速冲击下的断裂形貌特征,基于能量守恒原理构建层板的能量解析模型。模型考虑弹体动能被层合板的剪切破坏、拉伸断裂、压缩变形、分层损伤以及冲击区运动等损伤模式吸收,最终得到常微分形式的能量平衡方程。方程的几何参数中剪切充塞孔深度由试验弹道极限速度及理论求解得到,裂纹长度和分层损伤区域通过弹道冲击试验测量获得。在验证模型准确性的基础上,研究表明层合板在中速冲击时纤维拉伸断裂损伤吸收最多的能量,而高速冲击时压缩变形成为主要的吸能方式。在整个冲击过程中,较大的分层损伤区域使得基体的能量吸收作用不可忽视。层合板在平头弹冲击下与圆头弹相比吸收了更多的能量。     

芳纶纤维复合材料低速冲击响应实验研究

芳纶纤维因具有轻质高强、良好耐疲劳性和化学稳定性等优良性能,逐渐成为重要的国防军工材料。选用芳纶单向布和平纹织物设计并制备了不同结构参数的芳纶纤维复合材料层合板,采用落锤冲击试验仪在不同的冲击能量下进行低速冲击实验,根据最大接触力、能量吸收能力和凹陷深度评估层板的抗冲击性能。结果表明,[0/45/-45/90]s单向层合板的接触载荷峰值高于[0/90]s单向层合板和平纹织物层合板,并在高能量冲击下具有优异的能量吸收能力,其损伤区域最小。破坏形貌表明,单向复合材料层合板损伤以分层为主,而平纹织物复合材料层合板以整体塑性大变形为主,这为芳纶纤维复合材料的优化设计及防护应用提供一定的理论指导。     

复合材料层合板损伤区域扩展全过程分析

对碳纤维NCF层合板进行了2组准静态压痕试验。第1组采用不同的压头尺寸探究不同压头直径对层合板损伤区域和面积的影响;第2组进行固定压头尺寸的重复试验,使用非接触空气耦合超声波扫描试样损伤情况,研究静压痕力、凹坑深度、损伤面积三者之间的联系。利用Abaqus有限元软件,根据Hashin准则和内聚力单元的结合,对第2组层合板准静态压痕试验进行全过程的损伤扩展分析。分析结果表明,基体拉伸的破坏是层合板最容易出现的破坏,而且其损伤区域涵盖了其他4种损伤区域。凹坑深度与损伤面积存在一定联系,试验开始阶段凹坑增加速度缓慢,损伤面积增加速度较快;接近极限载荷时,凹坑深度增加速度加快,损伤面积增加速度减缓。     

基于模糊综合评价法和贴近度法的复合材料层合板低能量冲击损伤评定系统的设计

为了能够较为准确的预测复合材料层合板在受到低能量冲击损伤的程度,本文运用了模糊综合评价法和贴近度法两种评定方法,建立了复合材料低能量冲击表面损伤信息与其损伤程度之间的联系。并基于Matlab及相关的软件设计出复合材料层合板低能量冲击损伤评定软件。试验结果表明设计软件在损伤程度评定方面有优越性,对于复合材料结构件遭受低能量冲击后的检测提供了一种新的思路和方法。     

玻璃纤维复合材料层合板冲击后的压缩强度

对不同厚度的二维编织环氧玻璃纤维层合板进行落锤冲击试验及冲击后压缩破坏试验,以研究低速冲击对复合材料层合板剩余压缩强度(CAI)的影响。用透光描影及热揭层方法对冲击损伤形式进行描述。讨论了损伤宽度、损伤面积与冲击能量及剩余压缩强度、模量间的关系,并建立有限元模型,采用开口等效及软化夹杂等分析方法对材料的冲击后压缩强度值进行估算。     

复合材料加筋层合板准静态压痕实验研究及数值分析

利用ABAQUS有限元程序所建立了一种基于用户子程序USDFLD和Hashin强度准则的复合材料损伤计算模型,用该模型对复合材料加筋层合板在静压痕力作用下主要发生的纤维拉伸破坏、纤维微屈破坏、基体拉伸破坏、基体压缩破坏、层间拉伸破坏、层间压缩破坏这几种基本损伤模式进行分析。对复合材料加筋层合板在静压痕力作用下进行损伤全过程数值研究,利用该有限元模型预测复合材料层合板静压痕力作用下的荷载-位移曲线以及凹坑深度与静压痕力的关系曲线。数值仿真与实验结果吻合较好,表明该损伤模型方法的可行性。复合材料层合板加筋后拐点处的凹坑深度明显加大,达到0.84mm。通过对加筋板的刚度和强度失效规律的分析,为进一步的复合材料格栅加筋结构(如飞机结构中复合材料后压力框)的性能分析提供参考。     

Assessment of ablation damage on quartz ceramics through experiment and 3D modelling considering a dynamic heat source

The effects of irradiation time (IT), laser power (LP), and spot diameter (SD) on the damage caused to quartz ceramics under continuous-wave laser irradiation were investigated through an orthogonal experiment. The experimental results show that the LP has the dominant effect on the depth of an ablation pit, while the SD has the greatest impact on the diameter of the ablation centre. The diameter and depth of the ablation pit were both positively correlated to the irradiation energy. The bubbles and molten silica transition layer affected the laser beam's reflection and transmission properties, leading to the incident laser beam scattering into the entire ablation pit and forming an elliptical ablation pit. Furthermore, a 3D finite element (FE) model considering a dynamic heat source was developed to simulate the laser damage process. The shape and dimension of the ablation pit predicted by the FE model were consistent with those obtained through the experiment, demonstrating the effectiveness and rationality of the model. The FE analysis results show that the different ablation rates in the radial and depth directions significantly influence the morphology of the ablation pits. The temperature gradient in the transition region increases while the thickness of the transition region decreases as the LP increases. This indicates that a large LP will lead to greater thermal stress in this area and result in more microcracks.     

Simulation and experimental study on the surface morphology and energy lost of the target material under non-overlapping impact of angular particles

In order to further understand the effect of solid impurities on pipeline wall during erosion, the particle impact process without fluid was extracted for specific study. The effect of multi-impact particles on the wall of pipeline was studied experimentally and simulated. In this experiment, an improved ejection apparatus was implemented to carry out multi-impacts non-overlapping impingement by rhombic particles made of high speed steel(W18Cr4V) on the AA6061 aluminum alloy plate through changing particle angle, incident angle, orientation angle and impact velocity. As a result, each particle's penetration depth was investigated and particles' rebound trajectory can be described through this experiment as well as surface morphology of the target material after impingement. The ductile damage criterion, shear damage criterion and MSFLD damage criterion were jointly implemented in ABAQUS/CAE software to simulate the whole process of collision which proved to be effective by getting consistent result compared with experimental data. It is found that under the condition of continuous non-overlapping impact, the target material produces a small work hardening effect in the impact area by converting kinetic energy of moving particles into internal energy of plate so as to reduce the penetration depth of each impact particle.     

埋地管道点蚀生长的三维元胞自动机模拟

采用一个三维元胞自动机模型对土壤腐蚀环境中管道金属基体坑点的生长、演化过程进行研究。模拟结果得到了不同条件下管道腐蚀损伤过程的瞬像,并提出了蚀坑宽径比、蚀坑深度比及蚀坑形状参数等一系列腐蚀损伤参数,对管道腐蚀损伤程度进行了定量描述。     

碳纤维树脂基复合板料的铺层方式对低速冲击性能的影响

为研究碳纤维增强树脂基复合材料(CFRP)板铺层方式对低速冲击性能的影响,设计了一系列CFRP板的冲击试验。对CFRP板的铺层方式、冲击能量的形式进行调节和改变,获取CFRP板在各种条件下的低速冲击行为;再通过冲击实验和超声波扫描的方法研究冲击过程中CFRP板的铺层方式和冲头质量对碳纤维树脂基复合材料板冲击性能的影响。结果表明,在15 J的低能量作用下冲击CFRP板时,冲头的质量越大,该板对能量的吸收率越大,损伤面积也越大;相同能量和相同冲头质量的冲击情况下,铺层方式为[0°/45°/90°/-45°]_2的抗冲击性能最好。CFRP板的冲击载荷、能量吸收和损伤形态与冲击能量的大小以及冲头动量密切相关。     

高强玻璃纤维板抗高速破片侵彻性能试验

为了研究高强玻璃纤维板抗高速破片侵彻性能,开展了弹道试验,探讨了破片入射速度、靶板厚度对高强玻璃纤维板抗侵彻性能的影响,通过对弹道试验结果分析,指出了高强玻璃纤维板的变形失效模式、吸能特性和抗侵彻机理。结果表明:破片在侵彻高强玻璃纤维板过程中可视为刚体,高强玻璃纤维板迎弹面破坏模式为纤维剪切破坏并伴随纤维反向喷出,迎弹面弹孔附近区域出现基体碎裂、纤维脱粘;背弹面破坏模式为纤维拉伸断裂,背弹面损伤区域远大于迎弹面损伤区域;高强玻璃纤维板单位面密度吸能随着破片侵彻速度增加呈线性增加,在试验速度范围内,得出了立方体破片侵彻不同厚度靶板入射速度与剩余速度、入射速度与靶板单位面密度吸能关系。     

氧化石墨烯改性碳纤维复合材料抗冲击行为研究

使用单层纳米氧化石墨烯（NGO）粒子对环氧树脂进行改性处理,采用真空辅助树脂传递模塑成型工艺制备了[±45/0/90]_2S铺层角度下的纯树脂及单层NGO改性碳纤维复合材料（CFRP）层合板。通过落锤冲击试验、超声C扫描检测、冲击后压缩试验等对纯树脂及单层NGO改性CFRP进行实验研究。结果表明,纯树脂及单层NGO改性CFRP在损伤阻抗及损伤容限实验中均存在拐点现象,且拐点出现在相同深度位置,其中纯树脂CFRP拐点位置为0.51 mm,单层NGO改性CFRP拐点位置为0.43 mm;相对于纯树脂CFRP,单层NGO改性CFRP可以显著提高复合材料的抗冲击性能及冲击后的压缩性能;通过对冲击后凹坑深度及凹坑面积进行数据模拟,可以用拟合公式实现对复合材料的损伤预测。     

环氧树脂/玻璃纤维/碳纤维混杂复合板低速冲击及损伤检测

为研究玻璃纤维(G)铺层的位置对碳纤维(C)复合板冲击损伤程度的影响,分别在15 J和25 J冲击能量的条件下,采用落锤式冲击试验机对[CC]2s、[CCCG]s、[GCCC]s、[CCGC]s 4种复合材料分别进行冲击实验,得出接触力、能量和位移分别随着时间变化的曲线;然后采用水浸式超声波C扫系统对冲击后的复合板进行...     

A new approach to characterize scratch and mar resistance of automotive coatings

Mar damage is a major customer concern of the automotive coatings industry. Our study of mar performance can be separated into two distinct areas, a detailed understanding of the damage formation mechanism, and an investigation of the relationship between the damage morphology and appearance. We have developed a nanoscratch technique that can measure important physical quantities, such as penetration depth, normal force and tangential force during the formation of the scratch. Mar resistance of three coatings was evaluated and compared based on the damage mechanisms: plastic flow and fracture. The different deformation mechanisms result in different damage morphologies and a corresponding change in visual impact of the scratch. Statistical surveys of appearance of well-defined scratches indicate that in very short observation times, scratches where fracture has occurred are much more visible than those made by plastic deformation alone. However, with sufficient time and strong illumination a significant percentage of observers could see plastic deformation as well.     

Atomic simulation of textured silicon carbide surface ultra-precision polishing

In view of increasing accuracy requirements and difficult machining characteristics of silicon carbide materials, this paper proposes new machining method with ultra-high precision. Based on improvement of ultra-precision machining quality by textured surface, specific nano texture was machined on silicon carbide surface. Effects of different texture parameters on polishing force, polishing temperature, potential energy, dislocation, stress and friction coefficient were analyzed. Two typical textures (grooves and pits) with different sizes were compared. Simulation results show that surface morphology, polishing force and friction coefficient are improved with the increase in groove depth and pit depth. The smaller the groove spacing, the better the polishing quality and polishing behavior. In addition, groove texture can effectively inhibit the growth of dislocations and defect atoms during polishing. Compared with non-textured surface, textured silicon carbide surface can improve polishing conditions. It is found that groove texture has more beneficial effect on polishing quality than pit texture with the same size.     

聚晶金刚石复合片（PDC）放电修磨的实验研究

耐磨性是衡量PDC好坏的首要指标。通过实验验证：大规准高能量的放电会对聚晶金刚石层产生破坏,但是通过合理选用电规准,分级设置加工深度和相适应的脉冲参数,可以兼顾放电效率、表面粗糙度和对金刚石层的不良影响。通过对PDC的精细放电,放电后经过铸铁盘抛光,以及与纯粹机械研磨、铸铁盘抛光三者的磨耗比的对比,结果显示三者的耐磨性没有明显区别。