复合材料头盔壳体用超薄层合板冲击后的压缩性能

使用[0°/0°/0°]T、[45°/0°/45°]T两种铺层角度将碳纤维经面缎纹织物、碳纤维平纹织物预浸料、不同面密度芳纶纬编双轴向织物(MBWK)三种增强材料混杂铺层,制备出厚度为1.30 mm的复合材料头盔壳体用超薄层合板。测试分析了层板冲击后的压缩性能,用C扫描超声波检测仪测试了层合板冲击损伤图像,使用Image Pro Plus图像分析软件计算出不同冲击条件下的超薄层合板冲击损伤面积,研究了增强体结构类型、铺层角度对超薄复合材料层合板冲击后压缩性能的影响。结果表明,使用铺层角度为[45°/0°/45°]T的增强体结构可抑制层板沿纤维方向的冲击损伤裂纹的扩展,但是冲击点损伤破坏严重;纬编双轴向织物的面密度越大,则层板冲击后的凹坑深度越小。与其他铺层结构相比,当铺层角度为[0°/0°/0°]T时底层为碳纤维预浸料、中间层纬编双轴向织物面密度为630 g/m2、面层为碳纤维经面缎纹织物的复合材料超薄层板的冲击损伤面积与凹坑深度均最小,分别为225.28 mm2、0.16 mm,其剩余冲击后压缩强度达到最大值97.43 MPa,压缩强度保持率75.72%。这种结构,具有优异的冲击后压缩性能。     

复合材料层合板端部压溃试验研究EI北大核心CSCD

通过对T800复合材料层合板进行一系列的端部压溃试验,重点研究了长度、厚度、铺层顺序、触发角以及胶结压力等因素对复合材料层合板破坏模式和力学性能的影响。分析复合材料板在端部压溃过程中的载荷-位移曲线和观察试验样件端部破坏形貌,揭示其破坏机理。结果表明:复合材料平板的端部压溃过程为非稳态脆性断裂模式,而含45°触发角的复合材料层合板的端部压溃过程为层束弯曲破坏模式;在端部压溃试验中复合材料平板压缩强度随着厚度的增加逐渐上升,而长度的增加会减少其压缩强度,同时[45°/0°/-45°/0°]_(3s)铺层比[45°/90°/-45°/0°]_(3s)铺层拥有更好的抗轴向承载能力;触发角的加入会改变试件在压溃过程中的破坏模式并极大降低试件压溃时的压缩强度,是影响复合材料结构吸能能力的关键因素;研究还发现不同胶结压力下,复合材料层板的力学性能随着胶结压力的增加逐渐提高,但达到一定胶结压力值后,继续增加胶结压力力学性能反而下降。     

搭接长度和铺层方式对CFRP复合材料层合板胶接结构连接性能和损伤行为的影响

针对不同搭接长度和铺层方式的碳纤维增强树脂（CFRP）复合材料层合板单搭胶接结构进行了拉伸试验,观察了试件的受力过程和失效形态,获得了载荷-位移曲线;同时基于连续损伤力学模型和三维Hashin失效准则模拟了CFRP复合材料层合板的层内损伤形成和演化,并利用内聚力模型来模拟层间及胶层的失效损伤,对CFRP复合材料层合板单搭胶接结构在拉伸作用下的失效强度和损伤机制进行了预测,通过对比验证了该数值方法的有效性;通过数值试验比较不同搭接长度和铺层方式的单搭胶接结构及双搭胶接结构的连接强度和损伤行为,并提出了一种优化的CFRP复合材料层合板胶接结构。结果表明:CFRP复合材料层合板胶接结构的极限失效载荷随着搭接长度的增大逐渐增加并趋于稳定值,且结构的失效形式逐渐从胶层自身剪切失效过渡到邻近胶层的层合板层间分层失效;CFRP复合材料层合板胶接结构的连接强度和损伤行为随着铺层方式的不同而改变,通过对3种铺层方式的对比和分析,得到性能最好的铺层方式是[0₃/90₃]_2S;在搭接长度为5~20 mm时,通过对搭接长度进行优化,得到单搭胶接结构的最优搭接长度是17 mm,双搭胶接结构的最优搭接长度是19.3 mm,与搭接长度为20 mm相比,单搭胶接结构和双搭胶接结构的连接强度分别提高了13.26%和0.43%。      

三维织物间隔复合材料的力学性能

三维织物间隔复合材料是一种由垂向机织物连接两个平行织物平面的三维机织间隔复合材料,具有整体性好、可设计性强等特点。以玻璃纤维、碳纤维为原料,对三维间隔织物的结构进行设计,制备三维织物间隔复合材料,研究材料在平压和三点弯曲载荷作用下的力学特性,并分析纤维种类、夹芯层间距等结构参数对材料压缩、弯曲性能的影响。结果表明:随着夹芯层间距的增加,材料的压缩强度逐渐降低;材料的弯曲强度也逐渐降低,且纬向弯曲强度大于经向;采用碳纤维与玻璃纤维分别作为纬纱进行织造,前者制备的复合材料的压缩和弯曲强度均高于后者。     

铺层拼接层合板的抗拉强度

针对复合材料结构设计中遇到含铺层拼接的层合板强度预测问题,本文设计了含铺层交错拼接区的碳/双马复合材料层合板试件,采用拉伸试验方法测定了该材料的力学性能,得到了不同拼接长度层合板的抗拉强度。试验结果表明,铺层拼接状态差异对复合材料层合板的承载能力有显著影响,文中根据试验结果建立了抗拉强度随拼接长度变化的经验公式,为复合材料层合板结构的铺层设计和强度分析提供了理论依据。     

HF30F-24K碳纤维经编织物性能分析

对国产HF30F-24K碳纤维的力学性能、表截面形貌、单向和0°/90°经编织物性能及其复合材料性能进行了测试分析，结果表明：HF30F-24K碳纤维拉伸强度达到5000MPa以上，拉伸模量超过250GPa,且拉伸强度、拉伸模量和断裂伸长率的离散系数即C_v值全部低于5%,该产品具有较好的力学性能和稳定性，并具有典型的湿法纺丝工艺特点；HF30F-24K碳纤维单向织物经向断裂强力达到了3800N/25mm以上，0°/90°经编织物经向断裂强力超过了2800N/25mm,纬向断裂强力大于2600N/25mm; HF30F-24K碳纤维单向和0°/90°经编织物复合材料层间剪切强度分别为125.8MPa和77.2MPa,体现了湿法纺丝工艺碳纤维的界面结合优势，HF30F-24K碳纤维的单向和0°/90°经编织物预浸料复合材料也因此表现出较好的拉伸、压缩、弯曲性能。     

表面带金属层的复合材料层合板低速冲击数值模拟

使用Abaqus/Explicit建立表面带金属层的复合材料层合板和复合材料裸板低速冲击有限元模型,与已有文献对比验证结果的可靠性,研究结果对复合抗弹结构有很好的借鉴和参考价值.采用Johnson-Cook本构关系模拟铝合金和钛合金层的力学行为,选用Hashin准则对复合材料层内损伤进行失效判断,用二次应力准则来模拟粘结层Cohesive单元的层间失效.结果表明,相同铺层与冲击能量下,表面带铝合金层合板对内部纤维的保护性能优于表面带钛合金层合板,表面带钛合金层合板的抗冲击性能优于复合材料裸板;[§/0°/90°/0°/90°/0°]s铺层层合板的抗冲击性能优于[§/-45°/90°/0°/45°/-45°]s铺层层合板的抗冲击性能;在子弹刚冲破层合板与子弹完全离开层合板阶段,表面带铝合金层合板对子弹动能吸收率最大.     

基于断裂韧性预报复合材料层合板的开孔拉伸强度

开孔层合板的强度预报往往取决于孔边的临界长度,它不仅与材料性能,而且与铺层、孔径都有关。本文基于线弹性断裂力学,提出了一种预报对称铺层层合板开孔拉伸强度的新方法,只需提供正交层合板的断裂韧性和无缺口层合板的拉伸强度,显著降低对实验数据的依赖性。首先,将临界长度表作为层合板断裂韧性和无缺口拉伸强度的函数,再通过正交层合板[90/0]_8s的紧凑拉伸试验和虚拟裂纹闭合技术,确定出0°层断裂韧性,进而计算得到任意对称铺层层合板的断裂韧性。本文测试了T300/7901层合板[0/±45/90]_2s和[0/±30/±60/90]_s的开孔拉伸强度,孔径分别为3 mm、6 mm和9 mm。理论预报结果与试验值吻合较好,最大误差为15.2%,满足工程应用需求。      

碳纤维增强聚酰亚胺树脂基复合材料MT300/KH420高温力学性能(Ⅰ)——拉伸和层间剪切性能

研究了碳纤维增强聚酰亚胺树脂基复合材料MT300/KH420的高温力学性能,重点揭示了MT300/KH420的[0°]_7、[0°]_(14)和[±45°/0°/90°/+45°/0°_2]_s层合板在常温~500℃的拉伸和层间剪切性能的变化规律。结果表明:在350℃以内,[0°]_7层合板拉伸强度随温度升高有所提高,拉伸模量几乎不变,在420℃时拉伸强度和模量均出现明显下降,在500℃时分别保持在65%和83%以上,表现出优异的高温拉伸性能。MT300/KH420的[0°]_(14)层合板层间剪切强度在常温~420℃随温度升高不断降低至52.8%,在高温下呈现出黏弹效应,且在420℃时最为明显。相比于单向层合板,[±45°/0°/90°/+45°/0°_2]_s多向层合板高温力学性能较为稳定,且由纤维控制的纵向试件力学性能受温度影响较小。     

碳纤维增强聚酰亚胺树脂基复合材料MT300/KH420高温力学性能(I)——拉伸和层间剪切性能

研究了碳纤维增强聚酰亚胺树脂基复合材料MT300/KH420的高温力学性能, 重点揭示了MT300/KH420的[0°]₇、[0°]₁₄ 和[±45°/0°/90°/+45°/0°₂]_s层合板在常温~500 ℃的拉伸和层间剪切性能的变化规律。结果表明:在350 ℃以内,[0°]₇层合板拉伸强度随温度升高有所提高, 拉伸模量几乎不变, 在420 ℃时拉伸强度和模量均出现明显下降, 在500 ℃时分别保持在65%和83%以上, 表现出优异的高温拉伸性能。MT300/KH420的[0°]₁₄层合板层间剪切强度在常温~420 ℃随温度升高不断降低至52.8%, 在高温下呈现出黏弹效应, 且在420 ℃时最为明显。相比于单向层合板, [±45°/0°/90°/+45°/0°₂]_s多向层合板高温力学性能较为稳定, 且由纤维控制的纵向试件力学性能受温度影响较小。      

Prediction of bending strength of long corrugated boxes

Long corrugated boxes were supported at both ends and bent by a concentrated force applied at the middle. Boxes with different lengths, cross‐sectional shapes, flute directions and board strengths were tested, using a standard compression tester with a fixed platen in accordance with ASTM D‐642. An equation was developed to relate compression strength to the various properties of the box. The correlation coefficient R² for the fit to actual data was about 0.4. Boxes having the flutes run around the box had a 20% higher compression strength than with horizontal flutes. The most significant factor was found to be the board edge crush strength. The results suggest that failure of boxes in bending is due to localized crushing at the point of application of the load, rather than whole‐box collapse. Copyright © 2001 John Wiley & Sons, Ltd.     

The effect of adding nano-SiO2 and nano-Al2O3 on properties of high calcium fly ash geopolymer cured at ambient temperature

This article presents the effect of adding nano-SiO₂ and nano-Al₂O₃ on the properties of high calcium fly ash geopolymer pastes. Nano-particles were added to fly ash at the dosages of 0%, 1%, 2%, and 3% by weight. The sodium hydroxide concentration of 10 molars, sodium silicate to sodium hydroxide weight ratio of 2.0, the alkaline liquid/binder ratio of 0.60 and curing at ambient temperature of 23 °C were used in all mixtures. The results showed that the use of nano-SiO₂ as additive to fly ash results in the decrease of the setting time, while the addition of nano-Al₂O₃ results in only a slight reduction in setting time. Adding 1–2% nano-particles could improve compressive strength, flexural strength, and elastic modulus of pastes due to the formation of additional calcium silicate hydrate (CSH) or calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) or geopolymer gel in geopolymer matrix. In addition, the additions of both nano-SiO₂ and nano-Al₂O₃ enhances the shear bond strength between concrete substrate and geopolymer.     

新型4层瓦楞纸板的性能分析

研究了一种新型的4层瓦楞纸板结构,并将4层瓦楞纸板和3层、5层瓦楞纸板的平压强度、边压强度、戳穿强度和耐破度性能进行比较,最后得到新型4层瓦楞纸板的主要优点是:厚度比5层瓦楞纸板要薄,节省了夹芯纸的用量,降低瓦楞纸板的成本,而且强度高,在一定情况下可以代替5层瓦楞纸板达到抗压、防震、缓冲的目的。     

The role of 0–2 mm fine recycled concrete aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate concrete

The aim of this study is to investigate the role of 0–2 mm fine aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate (RCA) concrete with normal and high strengths. Normal coarse and fine aggregates were substituted with the same grading of RCAs in two normal and high strength concrete mixtures. In addition, to keep the same slump value for all mixes, additional water or superplasticizer were used in the RCA concretes. The compressive and splitting tensile strengths were measured at 3, 7 and 28 days. Test results show that coarse and fine RCAs, which were achieved from a parent concrete with 30 MPa compressive strength, have about 11.5 and 3.5 times higher water absorption than normal coarse and fine aggregates, respectively. The density of RCAs was about 20% less than normal aggregates, and, hence, the density of RCA concrete was about 8–13.5% less than normal aggregate concrete. The use of RCA instead of normal aggregates reduced the compressive and splitting tensile strengths in both normal and high strength concrete. The reduction in the splitting tensile strength was more pronounced than for the compressive strength. However, both strengths could be improved by incorporating silica fume and/or normal fine aggregates of 0–2 mm size in the RCA concrete mixture. The positive effect of the contribution of normal sand of 0–2 mm in RCA concrete is more pronounced in the compressive strength of a normal strength concrete and in the splitting tensile strength of high strength concrete. In addition, some equation predictions of the splitting tensile strength from compressive strength are recommended for both normal and RCA concretes.     

Yield strength in submicrovolumes of single crystals

The specificity of the transition from elastic to elastoplastic deformation in defect-free single crystals during the localization of the deformation in a submicron region has been studied by nanoindentation. A sharp transition from elastic to elastoplastic deformation has been observed in tested single crystals at depths of about 20–50 nm. To define the yield strength using the nanoindentation data, the stressed-strained state in the contact region has been analyzed. It has been shown that the yield strength in submicrovolumes of single crystals is tens-hundreds times higher than that at the macroscopic level and approaches the value of the theoretical shear strength. A mechanism of the transition from elastic to elastoplastic deformation has been discussed in the framework of the phenomenological model of the nucleation of dislocations. The transition has been induced by the homogeneous nucleation of dislocations in a contact.     

A practical model for efficient anti-fatigue design and selection of metallic materials:Ⅰ.Model building and fatigue strength prediction

The high cost and low efficiency of fatigue tests are bottleneck problem for the anti-fatigue design of metallic materials.For this problem,a theoretical fatigue model is proposed in this study,the possible applications have also been discussed.Specific results would be introduced in two serial papers,in which the first paper focuses on the model building and the applications on fatigue strength prediction;the second paper put emphasis on the influencing factors of the model parameters and the applications on fatigue strength improvement.In this first paper,a theoretical model is proposed considering both the strength and plastic restrictions of fatigue strength.As the model builds up a brief relationship among yield strength(Y),tensile strength(T)and fatigue strength(F),it is named as the Y-T-F model.Through the verification with fatigue strength data covering various kinds of metallic materials and loading condi-tions,this Y-T-F model exhibits both generality and accuracy.With the Y-T-F model,the efficient fatigue strength prediction could be conducted by brief linear fitting and calculation,just through yield strength,tensile strength and several known fatigue strength data.Moreover,through its deduced Y-F model,the analytical formula of fatigue strength continuously changing with materials strengthening can be obtained,as well as the maximum value of fatigue strength and corresponding critical yield strength.In summary,the Y-T-F model would be useful for reducing the fatigue tests,thus providing new possibilities on the efficient anti-fatigue design and selection of metallic materials.     

Concrete with ceramic waste aggregate

Use of hazardous industrial wastes in concrete-making will lead to greener environment. In ceramic industry about 30% production goes as waste, which is not recycled at present. In this study an attempt has been made to find the suitability of the ceramic industrial wastes as a possible substitute for conventional crushed stone coarse aggregate. Experiments were carried out to determine the compressive, splitting tensile and flexural strengths and the modulus of elasticity of concrete with ceramic waste coarse aggregate and to compare them with those of conventional concrete made with crushed stone coarse aggregate. The properties of the aggregates were also compared. Test results indicate that the workability of ceramic waste coarse aggregate concrete is good and the strength characteristics are comparable to those of the conventional concrete.     

碳/铝复合材料界面结合强度对拉伸性能的影响

本文主要研究C/Al复合材料先驱丝的界面结合强度的表征方法以及界面结合状态对复合材料拉伸性能的影响.用自行研制的小型剪切试验机测定复合材料先驱丝的纵向剪切强度,通过计算得到复合材料界面处的剪切强度以此作为界面结合强度的定量表征方法.实验证明,不同界面结合强度的复合丝在宏观上表现出有不同纵向剪切强度值,复合材料的界面结合强度可以用界面剪切强度值定量描述.复合材料拉伸强度随界面强度提高而减少,在满足复合材料横向强度要求前提下,降低复合材料界面结合有利于提高拉伸强度.     

High-Cycle Fatigue of Materials and Parts of Gas-Turbine Engines

We present a historical survey of the development of the scientific direction called “Structural Strength” at the Central Institute of Airplane Engine Manufacturing (CIAEM) for the last 30 years in connection with the 100th birthday of Academician S. V. Serensen, founder of this direction in the USSR, and the 75th anniversary of foundation of the CIAEM. We present the principal results obtained by the scientific staff of the Sector of Fatigue Strength of Materials of Gas-Turbine Engines at the CIAEM.__________Translated from Problemy Prochnosti, No. 3, pp. 5 – 21, May – June, 2005.     

膨胀螺栓与混凝土拉拔力的测试和分析

叙述了膨胀螺栓与混凝土拉拔力的设计准则和试验方法,并对影响拉拔性能的因素进行了分析和评价。