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。     

复合材料层合板冲击损伤剩余强度分析

民用飞机复合材料结构设计时必须考虑复合材料层合板的冲击损伤.通过试验测量和数值模拟两种方法分析碳纤维增强复合材料层合板低速冲击损伤后的剩余压缩强度,试验采用标准试验规范进行测量,数值模拟分析采用层内渐进损伤模型和层间Cohesive模型模拟分析层合板冲击损伤以及剩余压缩强度.数值模拟与试验结果对比表明,该数值模拟分析方...     

冲击位置对挖补修理层合板冲击后压缩性能的影响

使用过程中的低速冲击损伤对修理后的复合材料结构同样会造成威胁.设计并进行了复合材料挖补修理结构的低速冲击及冲击后压缩试验,测量了试验件的损伤投影面积和剩余压缩强度,分析了不同冲击位置的影响.结果表明,挖补修理层合板冲击后压缩强度比未修补板的低,挖补层合板对低速冲击位置较为敏感.冲击点离开挖补区一定距离后,挖补对层合板的低速冲击及其继后压缩性能的影响消失.     

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。     

CFRP层合板冲击后压缩失效分析数值模拟

复合材料层合板的损伤容限是复合材料结构设计的关键因素。针对碳纤维增强复合材料(CFRP)层合板低速冲击损伤和压缩破坏问题,本文基于连续损伤力学和粘结单元模型,在ABAQUS中对两种不同冲击能量下的层合板进行了低速冲击和冲击后压缩仿真分析,并对层内和层间损伤进行了研究,分析了层合板的冲击损伤与压缩失效行为,通过与试验结果进行对比,验证了该模型的有效性。研究结果表明:冲击损伤对层合板的剩余压缩强度有着重要影响,试件的破坏开始于冲击损伤区域,并逐渐扩展到层合板的边缘,压缩力快速下降,层合板最终失效。     

复合材料层合板损伤容限敏感性参数研究

本文针对碳纤维增强复合材料层合板冲击下的损伤容限参数敏感性进行分析.对复合材料层合板损伤容限的影响参数、纤维角度、铺层顺序、层合板厚度、冲击速度和冲击角度等进行冲击损伤仿真,采用蔡-吴强度准则评价层合板冲击的剩余强度,并对各参数影响的敏感性排序,确定纤维角度和铺层顺序为复合材料层合板冲击下损伤容限的敏感参数.     

准静态压痕作用下复合材料层合板损伤阻抗与损伤容限实验研究

参照标准实验方法,开展了复合材料层合板对准静态压痕力的损伤阻抗和损伤容限实验研究,获取了接触力、压痕深度、压头位移等实验数据,并对含静压痕损伤层合板进行了剩余压缩强度试验。研究了压痕深度-接触力与剩余压缩强度-压痕深度的变化关系,并讨论了准静态压痕过程中的损伤演变过程和层合板的压缩破坏模式。结果表明:当层合板表面出现目视勉强可见压痕时,初始损伤发生,压痕深度随接触力增大而明显增大,同时剩余压缩强度随压痕深度增加而明显降低;当达到最大接触力时,层合板失去承载能力,背面可看到大量纤维断裂。对于含静压痕损伤的层合板,压缩破坏模式为贯穿损伤区域的层合板断裂。     

基于渐进均匀化多尺度方法的CFR平纹机织材料冲击后压缩损伤研究

本文针对CFR平纹机织材料层合板低速冲击及冲击后压缩(CAI)响应和损伤问题,提出了一种渐进均匀化多尺度分析方法。基于渐进均匀化方法分别算出微观纤维束和介观子胞的等效强度和刚度,在这个基础上,采用三维Hashin失效准则以及连续损伤力学模型来模拟CFR平纹机织材料层合板的损伤起始和演化,用内聚力模型来模拟层间损伤。研究结果表明:CFR平纹机织材料低速冲击后压缩的仿真结果和试验结果吻合较好,验证了渐进均匀化多尺度方法的可靠性和准确性;随着冲击能量的递增,层合板的剩余压缩强度呈非线性下降。纤维损伤和基体损伤在低速冲击载荷下,随着冲击能量的增加,冲击损伤面积增大。而CAI行为则相反,压缩损伤面积随着冲击能量的增大而减小。     

多轴向经编/缝合织物增强复合材料冲击后压缩强度研究

本文采用冲击后压缩强度试验对多轴向经编／缝合复合材料的损伤容限进行了研究。结果表明：与层合板复合材料相比,多轴向经编／缝合复合材料的冲击后压缩强度提高了１００％以上,说明缝合对提高材料的抗损伤容限有较大的贡献。最后探讨了多轴向经编／缝合复合材料具有优越的综合性能及广阔的应用前景。     

低速冲击后三维中空夹层复合材料的压缩损伤容限

为了研究低速冲击后三维中空夹层复合材料的压缩损伤容限(剩余压缩强度),制作了满足要求的实验件并进行了剩余压缩强度对比实验.采用数码照片和外观检测等方法对压缩破坏损伤发展的过程进行了研究,分析了压缩破坏机理.结果表明,冲击损伤严重影响了三维中空夹层复合材料板的抗压能力,剩余压缩强度随冲击能量的增加而减少;三维中空夹层复合材料的压缩破坏主要由前面板控制,前面板发生局部屈曲的载荷与板的压缩破坏载荷几乎相等;表面蒙皮不仅能减少冲击损伤,而且能使板内的损伤显露在表面,容易让人发现.     

平纹编织碳纤维增强碳化硅复合材料低速冲击特性及冲击后的压缩强度

采用落锤冲击试验系统对平纹编织碳纤维增强碳化硅复合材料平板试样进行低速冲击,冲击能量为1.5～9J。冲击试验后,采用超声C扫描得到冲击损伤的大小。对含冲击损伤的试样进行压缩试验,通过与未冲击试样的压缩强度比较,得到冲击试样的剩余压缩强度。并对比了编织陶瓷基复合材料和树脂基复合材料的损伤阻抗和损伤容限。结果显示:随着冲击能量的增加,冲击力峰值、复合材料损伤面积和凹坑深度明显增加,到达峰值冲击力的时间减小。冲击能量的增加会导致冲击损伤面积的增加,而损伤面积的增加会导致剩余压缩强度的明显降低。相对于编织纤维增强树脂基复合材料,编织纤维增强陶瓷基复合材料的损伤阻抗较低,但损伤容限较高。     

脆性夹心复合材料层合板冲击损伤研究

通过冲击损伤试验，揭示了脆性夹心复合材料层合板的损伤机理，并提出了用于此类结构材料剩余强度预测的一套工程计算方法。     

Thermal shock effects on the impact resistance,tolerance and flexural strength of alumina based oxide/oxide ceramic matrix composites

In this study the effects of thermal shock on the impact damage resistance, damage tolerance and flexural strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates with balanced and symmetric layup were gradually heated to 1200°C in an air-based furnace and held for at least 30 min before being removed and immersed in water at room temperature. The laminates were then subjected to low velocity impacts via a hemispherical steel impactor. The resultant damage was characterized non-destructively, following which the laminates were subjected to compression tests. Three-point bend tests were also performed to evaluate the effect of thermal shock on the flexural strength and related failure modes of the laminates. Thermally shocked laminates showed smaller internal damage and larger external damage areas in comparison to their pristine counterparts. For the impact energy and resultant damage size considered, the residual compressive strengths for the thermally shocked and pristine laminates were similar.     

Reduced strength degradation of alumina–aluminium titanate composite subjected to low-velocity impact loading

The impact behaviour of monophase alumina and alumina–aluminium titanate monolithic composite ceramics that present flaw tolerant behaviour was studied. Low-velocity impact loading tests were performed on bending bars and the residual strength after the impact was evaluated by four-point bending tests. The impact tests were monitored using an instrumented drop-weight machine. During impact, the composites absorbed higher energy than the monophase material. The strength retention, in percentage, after the impact was significantly higher for the composite that presented damage tolerance for impact energy levels higher than monophase alumina. These results are discussed and fractographic analysis was used to identify the mechanisms responsible for the lower strength degradation of the composite.     

T300／QY8911层合复合材料低能量冲击后剩余压缩强度实验研究

本文对Ｔ３００／ＱＹ８９１１层合复合材料低能量冲击后的剩余压缩强度进行了实验研究,采用落锤（自由落体）冲击试验方法预制损伤,并利用Ａ扫描无损检测方法测定了冲击后损伤区的面积然后采用自行研制的板材压缩夹具（可防止试件在压缩过程中的整体失稳）,应用电测技术测定Ｔ３００／ＱＹ８９１１层合复合低能量冲击后剩余压缩中度,半考虑了湿热环境对其影响。     

Effect of stacking sequence on the compressive performance of impacted aramid fiber/glass fiber hybrid composite

Aramid fiber/glass fiber hybrid composites were prepared to examine the compressive performance of impacted composites. The effect of stacking sequence and surface treatment on compression after impact (CAI) performance of three‐layer hybrid composites was investigated with respect to delamination area. As the impact velocity increased, the laminates exhibited a significant reduction of compressive strength owing to larger delamination area within laminate. The surface treatment aramid fiber reduced the delamination area and enhanced the resistance to buckling. The strength reduction of laminate AAA was considerable because of wide delaminated region, whereas the residual strength of laminate GGG was not affected by impact energy because the laminate absorbed most of impact energy through formation of fiber cracks rather than delamination. Considering stacking sequence, the laminate GAG and GAA exhibited an energy threshold due to insensitivity to impact damage. As a result, the residual performance of composite was primarily dominated by delamination extent rather than fiber cracks.     

Design of damage tolerant and crack-free layered ceramics with textured microstructure

This work demonstrates damage tolerant behavior of ceramic laminates designed with residual stresses and free of surface edge cracks. Non-periodic architectures were designed by embedding 2 textured alumina (TA) layers between 3 equiaxed alumina-zirconia (AZ) layers. Compressive residual stresses of ∼ 250 MPa were induced in the textured layers. Indentation strength tests showed that textured compressive layers arrested the propagation of cracks. Results were compared to periodic architectures with the same volume ratio of TA and AZ materials. Crack propagation was arrested in both periodic and non-periodic designs; the minimum threshold-strength being higher in the latter. Non-periodic architectures with compressive layers as thin as ∼ 200 μm showed no evidence of surface edge cracks, yet still reached minimum threshold strength values of ∼ 300 MPa. In addition, the textured microstructure promoted crack bifurcation in the thin compressive layers and thus enhanced the damage tolerance of the material.     

Influence of cooling methods on high-temperature residual mechanical characterization of strain-hardening cementitious composites

Residual strength tests are commonly used to characterize the high-temperature mechanical properties of concrete materials. In these tests, the specimens are heated to a target temperature in a furnace and then cooled down to room temperature, followed by mechanical testing at room temperature. This research investigates the influence of the cooling method on the residual strength of Strain Hardening Cementitious Composites (SHCC) after exposure to 400°C and 600°C. Two types of cooling methods — furnace-cooling (within a closed furnace) and water-cooling (immersed in a water tank) — were adopted. Four different SHCC previously investigated by the authors for high-temperature residual mechanical and bond behavior with steel were studied. Two different specimen sizes were tested under uniaxial compression and flexure to characterize the residual compressive strength and modulus of rupture. The effect of the cooling method was prominent for the normalized residual modulus of rupture at 400°C, but not at 600°C. The cooling method had no effect on the normalized residual compressive strength of any material at either of the two temperatures, except one of the SHCC (PVA-SC) at 400°C. Specimen size also had no effect on the normalized residual compressive strength and modulus of rupture irrespective of the cooling method.