铺层结构对三维中空夹层复合材料压缩性能的影响

采用手糊成型制备了双夹层三维中空夹层复合材料,重点研究了厚度为5 mm和8 mm的三维中空织物ZK5和ZK8铺层顺序对复合材料压缩强度的影响,并从树脂含量、织物厚度匹配性角度进行分析。结果表明,随树脂含量增加,三维中空夹层复合材料的压缩强度明显提高;双夹层三维中空夹层复合材料中,下层的树脂含量明显高于上层;ZK5和ZK8织物铺层顺序对双夹层中空复合材料的压缩强度影响较大,其中将ZK8置于ZK5下层时复合材料的压缩强度为ZK8置于ZK5上层时的1.7倍,即在三维中空夹层复合材料总厚度不变的情况下,将高厚度中空织物置于下层的结构明显优于将其置于上层的结构。通过这一概念可以在保证三维中空夹层复合材料整体厚度尺寸不变、质量不增加的条件下通过铺层结构的匹配设计,最大限度地提高复合材料的力学性能。     

电热载荷对CFRP复合材料冲击后压缩性能研究

采用实验室电热载荷试验环境与测试平台,测试了CFRP复合材料在多种电流制度下试样的表面温度分布,并获得了CFRP复合材料电阻在不同电流强度下的变化规律,初步揭示了CFRP复合材料的电阻与电流强度之间呈线性递减的关系;对五种不同电流处理的CFRP复合材料进行了冲击后的剩余压缩强度试验(CAI)测试,试验后采用超声C扫描检测、外观检查与断口侧面宏观观察方法对损伤与失效特征进行了对比分析。研究结果表明,CFRP复合材料的剩余压缩强度随通入电流强度的大小呈先保持不变后下降的趋势,当电流超过20A时,试样表面冲击凹坑深度和冲击损伤面积增长较快,分层损伤与纤维断裂现象越来越严重。     

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。     

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.     

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...     

铝蒙皮整体中空夹层复合材料低速冲击的实验研究

本文采用落锤冲击试验机对铝蒙皮整体中空夹层复合材料进行了低速冲击试验.利用加速度传感器记录落锤冲击过程中加速度随时间变化曲线,通过数学处理得到了冲击栽荷、冲击点位移、材料损伤吸收能量随时间的变化曲线.探讨了铝蒙皮对整体中空夹层复合材料的低速冲击特性,如最大冲击载荷、冲击点最大位移和材料损伤时能量吸收等的影响.结果表明,附加铝蒙皮后,整体中空夹层复合材料的接触刚度、最大冲击栽荷以及材料的初始损伤能量都有明显增加.     

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。     

含圆形脱粘缺陷复合材料夹层结构侧向压缩破坏载荷与破坏模式分析

为分析含脱粘缺陷复合材料夹层结构侧压破坏载荷与破坏模式,采用损伤起始判据和损伤演化准则模拟面板与胶层的损伤及破坏过程,建立了考虑材料失效的三维渐进损伤分析模型。针对两种典型复合材料夹层结构,基于所建立的模型完成了破坏载荷预估和破坏模式分析,并将有限元分析与试验结果进行了对比。结果表明:面板较弱时,中部含圆形脱粘缺陷夹层结构侧压破坏模式通常为材料失效压缩破坏,随着载荷的增加,面板中部及脱粘区域周围发生损伤并沿板宽度方向向两侧扩展,直至材料完全损伤发生破坏;面板较强时,侧压破坏模式通常为整体失稳破坏,屈曲后结构基本不再具有继续承载的能力而迅速发生破坏。分析结果破坏载荷预估值与试验吻合较好,破坏模式与试验结果一致。     

缝合碳纤维泡沫夹芯复合材料低速冲击及损伤检测

研究了低速冲击对缝合与未缝合碳纤维泡沫夹芯复合材料冲击性能及损伤的影响;采用落锤冲击试验机对缝合和未缝合夹芯复合材料板分别进行了不同冲击能量下的冲击实验,得出冲击力和冲头位移分别随时间变化的曲线;采用水浸超声波扫描成像系统对冲击后的复合材料板进行损伤检测,得出夹芯复合材料板内部损伤情况。结果表明,在相同冲击能量下,缝合碳纤维复合材料板的冲击力较未缝合的要大,但冲头接触时间要短;此外,缝合碳纤维泡沫夹层复合材料板比未缝合的损伤面积要小,这说明缝线能有效的抑制冲击载荷下复合材料板内损伤扩散,减小分层损伤面积,提高复合材料板的抗冲击性能;缝合的抑制损伤效果在表面层和最内部层效果显著,而在中间层缝线的效果一般。     

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。     

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。     

ZTM陶瓷表面机加工损伤的初步研究

本文对热压烧结ＺＴＭ／ＳｉＣｐ陶瓷的表面机加工损伤及其对材料强度的影响进行了研究，发现机加工在陶瓷表面引入两类损伤，即机加工裂纹及机加工表面残余应力。材料在机加工后强度下降较大，而机加工后的退火处理则可以使强度有所提高。     

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.     

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。     

Study on the damage behavior of carbon fiber composite after low-velocity impact under hygrothermal aging

In this article, T800 carbon fiber/epoxy resin composite was subjected to hygrothermal aging. By analyzing the mass change, surface morphology before and after aging, infrared spectra, and dynamic mechanical properties, the effect of hygrothermal aging on the composite properties was studied. The hygrothermal aging of the composite after low-velocity impact, the effects of environmental factors on the damaged area, and the post-impact compression properties of composites were studied. The results showed that the saturation moisture absorption rate of the composite after aging (71°C constant temperature) was 0.88%. Upon increasing the impact energy, an indentation appeared before the inflection point at 35 J. When the impact energy was less than 15 J, aging did not affect invisible damage. Above this, the damaged area and number of internal cracks and defects in the composite were increased. After aging, the compressive strength of composite laminates with impact damage decreased obviously. During the aging stage, the residual compressive strength of the sample was the lowest in the moisture saturated state, and hygrothermal aging had little effect on the compression failure mode after impact.     

Effect of nano silica and fine silica sand on compressive strength of sodium and potassium activators synthesised fly ash geopolymer at elevated temperatures

Environment friendly geopolymer is a new binder which gained increased popularity due to its better mechanical properties, durability, chemical resistance, and fire resistance. This paper presents the effect of nano silica and fine silica sand on residual compressive strength of sodium and potassium based activators synthesised fly ash geopolymer at elevated temperatures. Six different series of both sodium and potassium activators synthesised geopolymer were cast using partial replacement of fly ash with 1%, 2%, and 4% nano silica and 5%, 10%, and 20% fine silica sand. The samples were heated at 200°C, 400°C, 600°C, and 800°C at a heating rate 5°C per minute, and the residual compressive strength, volumetric shrinkage, mass loss, and cracking behaviour of each series of samples are also measured in this paper. Results show that, among 3 different NS contents, the 2% nano silica by wt. exhibited the highest residual compressive strength at all temperatures in both sodium and potassium‐based activators synthetised geopolymer. The measured mass loss and volumetric shrinkage are also lowest in both geopolymers containing 2% nano silica among all nano silica contents. Results also show that although the unexposed compressive strength of potassium‐based geopolymer containing nano silica is lower than its sodium‐based counterpart, the rate of increase of residual compressive strength exposed to elevated temperatures up to 400°C of potassium‐based geopolymer containing nano silica is much higher. It is also observed that the measured residual compressive strengths of potassium based geopolymer containing nano silica exposed at all temperatures up to 800°C are higher than unexposed compressive strength, which was not the case in its sodium‐based counterpart. However, in the case of geopolymer containing fine silica sand, an opposite phenomenon is observed, and 10% fine silica sand is found to be the optimum content with some deviations. Quantitative X‐ray diffraction analysis also shows higher amorphous content in both geopolymers containing nano silica at elevated temperatures than those containing fine silica sand.     

内蒙古中部隆盛庄古建筑青砖墙体冻害损伤研究

经分析,冻融是造成隆盛庄古建筑墙体产生病害的主要原因。为了进一步研究严寒环境对古建筑墙体损伤劣化的影响,通过对青砖试样进行冻融试验,分析冻融前后质量、抗压强度和表面硬度的变化规律;基于Weibull分布,分别建立了质量、抗压强度和硬度3个指标下的冻融损伤模型,并通过统一3个损伤模型的形状参数(m)值对模型进行了修正。结果表明:青砖材料的抗压强度、质量损失量和表面维氏硬度随冻融次数的增加呈指数型下降;相同冻融循环次数下,表面硬度的损伤程度远比质量和抗压强度的损伤程度大;建立的Weibull损伤模型与试验曲线具有较高的吻合度,修正后的冻融损伤模型可以较好地反映青砖在严寒环境下的损伤规律。