The effects of sample type and stress ratio on fatigue crack growth rate and fatigue crack growth average life of YB-DM-11 plexiglass were studied. The results show that the type of samples has little effect on the fatigue crack growth rate of plexiglass,but the life of compact tension samples is longer than that of centrecracked tension（CCT） samples; for CCT samples,when the stress ratio is positive,its stress ratio and fatigue crack growth rate increase and its fatigue crack growth average life is reduced. When the stress ratio is negative,the crack closure effect causes the crack growth to accelerate,so that the crack growth rate at the negative stress ratio is greater than that at the positive stress ratio,but the life at the negative stressratio is significantly less than that at the positive stress ratio.

The high-temperature compressive properties are indispensable mechanical performance parameters for the structural design of composites, but it is difficult to be measured effectively by traditional techniques. In this study, the high temperature compressive experiment of carbon fiber reinforced plastics (CFRP) laminates was conducted in high-temperature experimental system based on digital image correlation (DIC) method. And the compressive properties, stress-strain curves and the evolution of axial full-field strain of CCF300/5228A with 0° and 90° ply-ups at 130℃ were obtained. Moreover, they were compared with those obtained at room temperature. Furthermore, the fracture analysis of the compressed specimens was carried out through scanning electron microscopy (SEM), meanwhile the effects of high temperature and lay-up on the compressive properties were discussed combining with the experimental results. Finally, an experimental verification was carried out and the results obtained demonstrated the feasibility and reliability of the experimental system and relevant experimental methods. The results show that the retention rate of 0° and 90° compressive strength at 130℃ are 70.5% and 62.6%, respectively, while the retention rate of compressive modulus are 88.0% and 75.4%, respectively, indicating that the strength and modulus of the laminates which are controlled by the matrix are more sensitive to high temperature.

The high-temperature compressive properties are indispensable mechanical performance parameters for the structural design of composites, but it is difficult to be measured effectively by traditional techniques. In this study, the high temperature compressive experiment of carbon fiber reinforced plastics (CFRP) laminates was conducted in high-temperature experimental system based on digital image correlation (DIC) method. And the compressive properties, stress-strain curves and the evolution of axial full-field strain of CCF300/5228A with 0 degrees and 90 degrees ply-ups at 130 degrees C were obtained. Moreover, they were compared with those obtained at room temperature. Furthermore, the fracture analysis of the compressed specimens was carried out through scanning electron microscopy (SEM), meanwhile the effects of high temperature and lay-up on the compressive properties were discussed combining with the experimental results. Finally, an experimental verification was carried out and the results obtained demonstrated the feasibility and reliability of the experimental system and relevant experimental methods. The results show that the retention rate of 0 degrees and 90 degrees compressive strength at 130 degrees C are 70.5% and 62.6%, respectively, while the retention rate of compressive modulus are 88.0% and 75.4%, respectively, indicating that the strength and modulus of the laminates which are controlled by the matrix are more sensitive to high temperature.

开展5224/CF3052平纹织物复合材料层压板低速冲击后的拉伸疲劳试验,冲击能量为1J/mm和3.4J/mm.绘制冲击能量为1J/mm时90％ 存活率的低周疲劳S-N曲线,分析冲击能量为3.4J/mm时最大应力变化对刚度降的影响.结果表明:层压板在低能量(3.4J/mm)冲击后具有优异的抗拉伸疲劳性能,冲击后层压板疲劳损伤不扩展(以106计)的应力水平超过有损静强度的90％;104循环—106循环刚度降随着拉伸疲劳最大应力的增大而增大.

In this paper,the curved beam strength and strength-after-impact characteristics of carbon/epoxy laminated curved beams were studied experimentally using four-point bending test and low velocity impact.First,the post impact damage characterizations of the laminated curved beams with different radii were analyzed based on ultrasonic C-scan images.Second,the effect of impact damage on both the failure strength and the maximum interlaminar radial stresses of the laminated curved beams were investigated.Finally,the full field displacement distributions of the laminated curved beams were obtained using Digital Speckle Correlation Method (DSCM).Experimental results play a significant role for strength evaluating of laminated curved beams with and without impact damage.

The effect of the different stress ratios (R) and annealing treatment on the fatigue properties of the transparent polycarbonate (PC) sheet and the mechanism behind were studied,the fatigue crack propagation (FCP) process and mechanism were analyzed.The results show that after annealing,the residual stress of the PC samples decreases obviously and the fatigue properties are greatly improved.This is because the machining process results in tensile stress in the PC samples,eliminating the tensile stress can improve the fatigue property of PC effectively;under the positive stress ratio (tensile-tensile fatigue),as the stress amplitude increases,the fatigue properties of PC decreases obviously,however,the negative stress ratio (tensile-compression fatigue) causes complex influence on the fatigue properties of PC.The fatigue fracture morphology suggests that distinct crack source,stable crack extension zone and instability zone exist obviously in fatigue fracture of PC.The mechanism of the fatigue crack propagation of PC indicates that crazes are initiated at first under the cycling stress,when the stress is higher than the strength of the fibrils in crazes or the fibrils are broken under the cycling stress,crazes develop into cracks.

The fatigue crack propagation behavior of two different forms of PMMA was studied using two-stage zone model. First, the fatigue crack length and fatigue crack propagation velocities of different specimens were obtained experimentally. Then the effect of material forms and specimen types on the fatigue crack propagation velocities was analyzed. Finally, the data scatter of da/dN-ΔK curves in different forms and different types of specimens was analyzed. The results show that the expressions of fatigue crack propagation velocities of middle crack tension (MT) specimens and compact tension (CT) specimens in the same form PMMA are similar. And the scatter of MT specimens is larger than CT specimens in two forms of PMMA.

阐述了航空行业标准“硬质塑料压缩性能试验方法”标准编制过程中的几个主要问题,包括编制原则、标准的适用范围、试样的形状和尺寸、结果的计算方法等,并结合相关材料试验对标准进行了试验验证.

运用三点弯曲加载方式对3238A/EW250F复合材料的弯曲疲劳性能进行了研究.结果表明:该复合材料弯曲疲劳寿命的分散性较小,所有试验点的疲劳寿命都满足90％置信度的中值寿命;所有试样均在有效部位发生破坏,且试样表面出现分层后,还有较长的一段寿命期;试验测得0°方向铺层3238A/EW250F复合材料的条件疲劳极限以动应力表示为σr=73.2 MPa.

The fatigue life of aeronautical perspex was studied on the basis of the fatigue S—N curves and fatigue diagrams of constant life.The research results showed that the Goodman model of organic glass fatigue life diagram not only itself had a very high correlation coefficient,at the same time could well predict a life of material under the safety coefficient,was fitting aeronautical perspex and other life diagram model.Goodman model life made the test personnel clearly find every point corresponding to the σ_(max),σ_(min),σ_a,σ_m.R and N,so as to the test time and cost were saved;and the safety coefficient and safety zone of a working point could be calculated by the known allowable safety coefficient,which would provide a basis for structure desiga

Some key problems were summarized,which were often happened in mechanical property tests for polymer matrix composites. The main factors effecting on tested results were analyzed,for example,which were alignment and failure mode in tension test,loading device and grips,percent bending and failure mode in compression test,span-to-thickness ratio and failure mode in flexural tests and inter-laminar shear tests. Reasons resulting to these problems were revealed,and some ways of approaching these problem were found. It was proofed that these ways had lead some good effects to engineering mechanical property tests for polymer matrix composites.

Fatigue properties of composites are studied, the typical composites fatigue performance is tested and test results are analyzed and discussed, conclu-sion is obtained: (1)the dispersivity of the fatigue life of composite materials is larger, especially in the low life expectancy, so the fatigue life of individual points cannot meet the 90%conifdence level of the value of life;(2)ob-servation from fatigue test process ifnds when the sample surface appears layer, it still has a long life period; (3) through the fatigue test results of plus or minus 45° brick composites fatigue limit condition isσr=91.656MPa.

胶粘剂在常温、盐雾和湿热环境中的力学性能日益受到人们的广泛关注.本研究采用对比试验法对试验结果进行分析,并对不同规格胶粘剂的环境耐久性进行了评价,以期为胶粘剂的寿命预测技术提供必要的理论依据.

Tensile fatigue S-N curves and conditions fatigue strength of aviation perspex were obtained by tensile fatigue test and effect of stress ratio on fatigue properties of the aviation perspex was studied. The results show that the conditions fatigue strength of the perspex were 63.0, 57. 3, 48. 4 MPa under the condition of stress ratios were 0. 4, 0. 1, --0. 4. The tensile fatigue S-N curves integrally moved up with the increase of stress ratio. Under the same stress level, specimens tested with higher stress ratio had longer fatigue life.

YB-DM-3有机玻璃因其具有良好的透光性和力学性能,目前在飞机上已经得到广泛应用,它是一种区别于金属材料的高分子材料,通过对有机玻璃拉伸疲劳性能的测试得到了疲劳S-N曲线和条件疲劳极限;比较了不同应力比下的有机玻璃拉伸疲劳S-N曲线,随着应力比的增加曲线整体上移.

With superior light transmission and mechanical performance,perspex has been widely used in aircrafts.Based on the mathematic models for tensile fatigue properties of metals,three models describing the tensile fatigue S-N curves of perspex were put forward,named power function,exponential function and three-parameter logarithmic function.According to the analysis of tensile fatigue testing results of aeronautic perspex,it is concluded that the three mathematic models are all suitable for describing the tensile fatigue properties of perspex,and the three-parameter logarithmic function is the most accurate one among them.

The accelerated aging experiments for perspex specimens have been conducted for 70 days under the conditions of heat air(50 ℃) and hygrotherm air(50 ℃,relative humidity 85%) and ultraviolet(50 ℃,313 nm wavelength) and tap water(50 ℃) and brine(50 ℃,3% NaCl Solution).The macro-mechanical characteristics of perspex were tested at different time during the experiments in different environment,and structure difference were analyzed between samples before aging and after aging by methods of GPC and DSC.Combined with the mechanical data,the aging rule and aging mechanisms for perspex in above typical environment were clarified qualitatively.

The tensile strength of glass fiber reinforced composites was tested using tensile method at different temperatures and the strength distribution was studied on simple linear regression. The tensile strength at different temperatures was fitted,furthermore,the tensile strength at lower temperature was predicted,and the predicted results are basically in agreement with the experimental data.The present work established a referrence for the application of glass fiber reinforced composites.

The accelerated aging experiments for PMMA specimens have been conducted for 70 days under the conditions of ultraviolet air(50℃ temperature,313nm wavelength),and macro-mechanical characteristics of PMMA were tested at different time during the experiments,and structure difference were analyzed between samples before aging and after aging by methods of GPC and DSC.Combined with the mechanical data,the aging rule and aging mechanisms for PMMA in ultraviolet were clarified qualitatively.

The research progress of the aeronautical perspex aging is presented including aging properties, experimental method, and atmospheric aging lifetime. The research works in this field, which should be done in the future, are shown.