三向正交C/C复合材料弹性性能预测与分析

根据三向正交C/C复合材料的细观结构,建立典型单胞模型,运用均匀化法预测了材料的9个工程弹性常数,与试验值误差较小。采用预测的弹性常数对三向正交C/C复合材料开孔板的拉伸力学行为进行有限元模拟,得到的孔边应变与试验值吻合。讨论了该材料偏轴向弹性性能,分析了组分性能对材料弹性性能的影响。材料主方向拉伸模量主要由纤维控制,剪切模量由基体控制,当偏轴角为45°时,面内剪切模量转为纤维控制。     

纳米SiO2包覆硅灰石填充改性尼龙1010的摩擦学性能

以硅灰石和水玻璃为主要原料,用无机化学沉积法制备纳米SiO2包覆硅灰石复合颗粒;利用扫描电镜和X射线衍射分析对包覆效果进行表征。将复合颗粒填充到尼龙1010中,对此复合材料进行拉伸、硬度和摩擦磨损实验,并与分别用硬脂酸改性硅灰石、未处理硅灰石填充的尼龙复合材料进行对比。结果表明,将纳米颗粒包覆硅灰石填充到尼龙1010中,可获得较好的结合界面,提高了尼龙复合材料的拉伸强度和硬度,比硬脂酸改性和未经处理的硅灰石更有效地改善了尼龙的摩擦学性能。     

有机填料填充聚四氟乙烯复合材料摩擦学及力学性能

采用共混-冷压-烧结-整形的工艺制备有机物填充聚四氟乙烯(PTFE)复合材料,考察相同含量的不同有机填料对PTFE复合材料力学性能和摩擦学性能的影响。结果发现,加入有机填料后,复合材料的拉伸强度降低,但硬度和压缩强度均提高;有机填料有效地改善了PTFE复合材料的摩擦学性能,其中,质量分数15%聚苯酯填充的PTFE复合材料减摩效果最好,质量分数15%聚酰亚胺填充的PTFE复合材料的耐磨损性能最优。相比之下,质量分数15%芳纶填充的PTFE复合材料摩擦磨损性能及力学性能最好,其耐磨损性能较纯PTFE提高了近400倍,而摩擦因数仅为纯PTFE的84%。其原因在于芳纶的加入有效地改变了摩擦机制,能形成均匀连续的转移膜,进而降低了磨损。     

不同体积分数SiCp/Al复合材料精密磨削试验研究

对体积分数为40%和60%的SiC_p/Al复合材料进行ELID精密磨削试验。分析了体积分数对加工材料物理化学性能的影响;运用正交试验和极差分析方法探究了磨削深度、砂轮线速度、电解电流及占空比对磨削加工表面质量和精度的影响规律,并得到优化工艺参数。采用相同优化工艺参数,对不同体积分数SiC_p/Al复合材料进行ELID精密平面磨削试验,对所得到的加工样件表面质量、形貌和机械加工性能进行分析研究。试验结果表明:SiC_p/Al复合材料ELID精密磨削加工表面质量和机械加工性能随着体积分数的增加而降低。采用ELID磨削技术可以实现对SiC_p/Al复合材料的精密加工,加工样件的表面粗糙度为95nm和106nm。     

纳米SiO_2、硅灰石复合填充PA1010复合材料的摩擦学性能研究

用纳米SiO2机械包覆硅灰石填充尼龙1010制备复合材料,对复合材料进行拉伸、硬度和摩擦磨损实验,并与纯硅灰石填充尼龙1010的复合材料进行对比。结果表明:纳米SiO2机械包覆硅灰石填充尼龙1010大幅度提高了尼龙复合材料的耐磨性,降低了摩擦因数;当纳米SiO2/硅灰石复合颗粒填充质量分数为20%时,复合材料达到最低摩擦因数0.307和最低磨损量1.27 mg,分别比纯尼龙降低了51.35%和55.86%。     

纳米及微米石墨/聚四氟乙烯复合材料的力学与耐磨性能

用热压成型法分别制备了纳米、微米石墨填充聚四氟乙烯(PTFE)的复合材料,对纯PTFE和复合材料进行了硬度、耐磨性和拉伸试验,用SEM观察了拉伸断口形貌.结果表明:纳米和微米石墨均能提高复合材料的硬度和耐磨性,而复合材料的抗拉强度和断后伸长率均有所下降;纳米石墨/PTFE复合材科的硬度、耐磨性、抗拉强度和断后伸长率均比微米石墨/PTFE复合材料的高;当纳米石墨质量分数为7%时,复合材料的综合性能较好,当质量分数大于7%后,复合材料的断后伸长率迅速下降;纳米石墨与PTFE相容性较好,在PTFE中的分布均匀.     

石英纤维增强酚醛多孔复合材料的制备及性能

以耐高温酚醛树脂为基体,石英纤维为增强体,热膨胀型微胶囊及空心玻璃微珠为填料,通过模压法和热膨胀法相结合制备了新型石英纤维增强酚醛多孔复合材料。采用扫描电镜、热重分析及力学性能测试,研究了不同热膨胀型微胶囊含量对复合材料微观组织及性能的影响,并通过断口形貌分析,揭示了该多孔材料的结构失效模式。结果表明：采用热膨胀法制备的隔热材料泡孔结构完整,闭孔率高,材料的隔热性能优异。当热膨胀型微胶囊含量为20wt%时,材料的综合性能最好,进一步提高微胶囊含量会导致开孔空隙率升高,材料的隔热性能降低。材料的断口形貌分析表明,复合材料中石英纤维与基体结合良好,界面强度适中,材料在拉伸和压缩应力下表现出非脆性断裂特征。     

复合材料开孔层合板有限元网格划分方法研究

对复合材料开孔层合板有限元建模过程中网格划分方法进行量化研究。应用参数化的方法建立多种板宽孔径比、多种铺层比例的开孔层合板模型,逐级调整网格密度,计算单轴拉伸载荷作用下孔边最大应力集中系数。根据有限元结果,结合牛顿插值的数值计算方法,模拟出开孔层合板合理的网格密度划分方程。然后,对该网格划分方程下计算的数值解进行试验验证与解析解验证。结果表明,这种网格密度划分方程能有效地降低计算误差,可以在板宽孔径比大于3的复合材料开孔层合板的有限元计算中广泛使用。     

石英粉填充聚四氟乙烯复合材料的蠕变性能

以石英粉为填料,通过机械混合和冷压烧结的方法制备石英粉填充改性聚四氟乙烯复合材料,研究复合材料的硬度、抗拉强度、压缩与回复性能和长期压缩蠕变性能.借助SEM探讨拉伸断面的微观结构.结果表明:加入适量的石英粉可以提高复合材料的硬度、抗蠕变性能,改进PTFE压缩与回复性能;但由于存在相界面缺陷,复合材料的抗拉强度降低.当粉石英质量分数在20%-30%之间时,其综合性能能够满足密封材料的要求.     

纳米ZnO填充PTFE复合材料的力学及摩擦学性能

通过机械搅拌和超声分散制备纳米ZnO填充PTFE复合材料,研究纳米ZnO填充量对复合材料力学及摩擦磨损性能的影响。结果表明:当ZnO质量分数小于3%时,复合材料的拉伸强度与纯PTFE相比略有增高;复合材料的密度、硬度、摩擦因数随ZnO填充量的增加而逐渐增大;当ZnO填充质量分数为1%～3%时,复合材料的磨耗量大幅下降,但若继续增加ZnO填充量,复合材料的磨耗量却变化不大。     

Fracture prediction of thin plates under hemi-spherical punch with calibration and experimental verification

The response of thin clamped plates subjected to static punch indentation is investigated experimentally, analytically and numerically to determine the onset of fracture. The accumulated equivalent plastic strain with stress triaxiality as a weighing function is introduced as ductile fracture criterion in the finite-element simulation and analytical prediction. The fracture criterion was calibrated by finite-element simulations of uniaxial tensile tests. Based on the calibration, and calculated distributions and histories of stress and strain, the critical location, and penetration to fracture were predicted within 5–10% accuracy for three punch radii.The plots of force–penetration and locations of fracture initiation in the static punch indentation tests were compared with finite-element simulations and analytical approximations showing good agreement. The transverse deflection profiles of the plates at the point of fracture obtained numerically were shown to agree well with the closed-form solution derived by taking into account a variable stress ratio and varying stress triaxiality. The strain distribution along the plate radius is influenced by the friction between the interfaces of punch and plate. By changing the friction coefficient, the fracture-forming limit diagram was constructed numerically. The present procedure can replace the time-consuming experimental technique in which the strain path is controlled by changing the radius of a cut off.     

含缺陷铝合金厚板预拉伸断裂研究

由于材料中存在空洞等缺陷,铝合金厚板在预拉伸过程中易发生断裂,对拉伸设备造成损伤。基于GTN损伤本构方程,建立铝合金板预拉伸断裂模型。基于小试件拉伸断裂试验测试结合数值模拟,确定GTN损伤本构参数,对五种典型厚度铝合金板预拉伸断裂进行研究。计算铝合金板断裂过程中的应力应变及损伤变量的变化规律,并将表面位置和断裂截面位置处的各变量进行对比。结果表明,随着拉伸率的增大,铝合金板由平面应力状态变为应变集中,其部位由正中心位置向边缘偏移,空洞体积分数最大值也由正中心位置转移到应变集中处;随厚度增加断裂应变略有降低,且受初始空洞体积分数的影响较大。通过对不同厚度、不同拉伸率的铝合金板预拉伸分析,得到初始空洞体积分数和初始缺陷尺寸随厚度变化规律。     

The elastic-plastic wrinkling of rectangular plates subjected to locally uniform tension

After overcoming the difficulty with discontinuity in boundary conditions, the pre-buckling elastic stress field for a rectangular plate subjected to locally uniform tension is given. An iteration procedure for solving an elastic-plastic plane stress problem is developed, so as to obtain the pre-buckling elastic-plastic stress field for the same plates. The effects of the aspect ratio of plates, tensile non-uniformity and material properties upon the stress field are also discussed. By assuming the shape of wrinkling region and the wrinkling mode in it, the dependences of critical wrinkling load and the size of wrinkling region upon the material and geometrical parameters are revealed. It is found that wrinkling is dominant by a combined parameter in elastic case or in plastic case.     

2A12铝合金圆波纹夹芯板抗平头弹冲击特性的试验研究

为研究铝合金圆波纹夹芯板对平头弹体的抗冲击性能,通过一级气炮系统开展弹体冲击铝合金圆波纹夹芯板以及等面密度单层均质板的试验.基于冲击试验数据,分析圆波纹夹芯板对弹体冲击的防护性能、失效模式和能量吸收情况,并与单层板进行对比,以获得两种靶板抗冲击性能的差异及原因.研究结果表明:弹体冲击圆波纹夹芯板的弹道极限速度低于单层板...     

温度对机械密封金属波纹管力学性能的影响

为了研究温度对机械密封金属波纹管力学性能的影响,建立高温泵用机械密封焊接金属波纹管计算模型,利用ANSYS软件计算波片的温度场,并通过间接耦合法计算不同介质温度下的热应力与热应变场,得到温度对波纹管力学性能的影响规律.计算结果表明:在高温工况下波纹管波片内产生了较大的热应力和热应变,增大了波纹管断裂、失弹等形式的失效的危险,在设计和使用过程中必须对此引起足够重视;在高温工况下波纹管波片等效热应力、热应变的最大值均出现在波片波谷处.     

冷轧生产工艺对1100铝合金板塑性应变比与杯形件制耳率的影响

采用拉伸试验测定了三种不同冷轧工艺生产的1100铝合金板的塑性应变比,并通过各向异性分布函数对其进行了拟合处理;同时采用晶体取向分布函数(ODF)对其织构进行了检测,最后与拉深试验中的制耳率进行了对比,确定了合理冷轧生产工艺。结果表明:不同工艺生产的板材的拉伸性能表现出不同的各向异性,从而产生不同的制耳,其中尤以塑性应变比对制耳的影响最为明显;当冷轧生产工艺采用(550~580)℃×16 h中间退火时,通过改变织构组分及比例降低了板材的各向异性,满足了板材拉深杯形件对制耳率的要求。     

A new hyperbolic shear deformation theory for buckling and vibration of functionally graded sandwich plate

A new hyperbolic shear deformation theory taking into account transverse shear deformation effects is presented for the buckling and free vibration analysis of thick functionally graded sandwich plates. Unlike any other theory, the theory presented gives rise to only four governing equations. Number of unknown functions involved is only four, as against five in case of simple shear deformation theories of Mindlin and Reissner (first shear deformation theory). The plate properties are assumed to be varied through the thickness following a simple power law distribution in terms of volume fraction of material constituents. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. Equations of motion are derived from Hamilton's principle. The closed-form solutions of functionally graded sandwich plates are obtained using the Navier solution. The results obtained for plate with various thickness ratios using the theory are not only substantially more accurate than those obtained using the classical plate theory, but are almost comparable to those obtained using higher order theories with more number of unknown functions.     

岸边集装箱起重机节点板的有限元分析与比较

针对常见的长腰形节点板与圆形节点板,利用ANSYS软件对岸边集装箱起重机钢结构进行有限元建模,分析比较两种形状节点板的应力分布情况.通过分析对比,发现两种形状的节点板在应力分布上呈有相同的规律,也存在一些不同现象.结合二者优点,可使节点板的形状得到优化设计,有效地发挥自身作用,减少不必要的材料浪费.     

The stress and strain concentrations of out-of-plane bending plate containing a circular hole

The elastic stress and strain fields of a finite thickness plate containing a circular hole subjected to out-of-plane bending are systematically investigated using the finite element method. It is found that the stress and strain concentration factors of the finite thickness plate are different except at the notch root of the free surface even if the plate is in elasticity state. The through-thickness distributions of strain components are not linear with the distance from the mid-plane in the stress concentration region. The nonlinearity of these distributions is very severe near the free surface especially in thick plate. The Euler-Bernoulli hypothesis and Kane-Mindlin's plate theory may not be reasonable to be used in the stress concentration region especially near the free surface. The maximum stress and strain do not always occur on the free surface and their locations depend on the moment ratio and the plate thickness. The maximum stress and strain concentration factors occur on the free surface only in thin plates of small moment ratio. The differences between the maximum value and surface value of stress concentration factor increase with the plate thickness and the moment ratio. This relation of strain concentration factor is similar to the one of stress concentration factor. But the difference magnitude of stress concentration factor is larger than that of strain concentration factor in same plate.