【作者】 张豪；

【导师】 张征；

【作者基本信息】 浙江工业大学 ， 机械工程， 2019， 硕士

【摘要】 对比常规的直线铺设复合材料层合板,变刚度多稳态复合材料层合结构的纤维角度、材料属性和层数并不固定,给科研工作者提供了极大的设计空间。和常规的纤维直线铺设复合材料层合板比较,变刚度多稳态复合材料层合结构有许多优点:合理分布应力,减轻结构质量以及具有极大的设计自由度,通过有效的组合获得两种或两种以上的稳定状态,并通过智能控制材料、湿度温度载荷或者机械载荷等外在驱动方式进行不同稳态间的转变。以上优点,使变刚度多稳态复合材料层合结构在空间延展变形装置、赛车定风翼和大型风力叶片等许多领域具有广泛的应用需求。受特征参数变化影响,变刚度多稳态复合材料结构在实际应用过程中出现了许多新的问题,深入了解特征参数对变刚度多稳态复合材料结构影响规律对于新型复合材料结构的发展至关重要。本文主要通过理论、有限元数值模拟和实验研究对变刚度多稳态复合材料层合结构进行了研究,获得了铺设角度、材料属性、层数和湿度参数影响规律,并以特定场合下人体手肘、膝盖康复过程进行分析,对变刚度多稳态复合材料结构在人体外骨骼的潜在应用进行相关研究。主要研究内容如下:1.基于经典层合板理论建立变刚度多稳态复合材料层合结构的理论稳态构型,并预测了不同的稳态形状和稳态中面曲线位置。理论模型显示,反/正/反型变刚度多稳态复合材料层合结构第一稳态呈现中间弯曲、两边平直的状态;第二稳态中间弯曲,但曲率方向与第一稳态相反,两端也呈现弯曲状态,曲率方向与中间部分相反。正/反/正型变刚度多稳态复合材料层合结构第一稳态在左右两侧有较大的扭转现象,左右两侧的曲率方向与中间凸起部分曲率方向相反;第二稳态在左右两侧平直,在中间部分有扭转。2.为研究特征参数对变刚度多稳态复合材料层合结构在稳态转变过程中的影响规律,通过有限元方法研究了铺设角度、材料属性、层数和湿度的影响规律。研究表明,在反/正/反型试件中,层数较小的试件稳态到达第二稳态时的位移数值大于层数多的试件。而伴随着层数的变多,最大载荷数值在增大。正/反/正型试件到达第二稳态的位移随层数的增大而变大。湿度对反/正/反型试件最大载荷影响明显,随着湿度变大,最大位移减小。湿度不影响正/反/正型试件在稳态转变过程中的载荷-位移曲线趋势,但随着湿度变化的增大,试件的最大载荷与最大位移均变大。3.对实验试件进行稳态转变实验,获得载荷位移-曲线。采用热压冷却法制备表面平顺完整、稳态可保持的实验试件。通过实验方法,利用经改装的拉伸试验机测试平台得到变刚度多稳态复合材料结构在稳态转变之间的载荷-位移曲线,验证了铺设角度、材料属性、层数和湿度对变刚度多稳态复合材料结构变化规律,反/正/反型试件的最大载荷位移略大于正/反/正型试件。材料属性不会改变相同铺设角度的载荷—位移曲线变化趋势。层数对变刚度多稳态复合材料层合结构的载荷—位移曲线不同,反/正/反型和正/反/正型试件变化规律相反。湿度可同时改变最大载荷数值和转变到第二稳态时的位移。4.对变刚度多稳态复合材料结构在人体外骨骼中的应用进行初期探索性研究。当手肘、膝盖保持弯曲状态时,变刚度试件处于一个稳态构型;当手肘、膝盖转过一定角度保持伸直状态时,变刚度试件处于另一个稳态构型。由于固定的材料属性、铺设角度、层数及湿度环境导致变刚度试件在每个稳态具有固定的外形,通过测量每个试件在稳态时的夹角,确定试件在人体外骨骼中的应用性,展现了复合材料在人体外骨骼结构广泛应用前景。更多还原

【Abstract】 Variable stiffness multi-stable composite laminate structure is not fixed at each composite laminate,it gives designers greater freedom.Variable stiffness composite laminates offer several advantages over traditional straight composite laminates,such as avoiding stress concentrations,weight loss potential,and highly designability.With two or more combinations through effective combinations for more than one steady state,the transition between stable states can be performed by external driving method such as mechanical load,smart material or temperature field.The above advantages have broad application prospects for variable stiffness and multi-stable composite structures in aerospace deformable mechanisms and wind turbine blades.Affected by the variation of characteristic parameters,many new problems have appeared in the practical application of variable stiffness multi-stable composite laminate structure.The in-depth understanding of the influence of characteristic parameters on the structure of variable stiffness multi-stable composite laminate structure is crucial for the development of new composite structures.In this paper,variable stiffness multi-stable composite laminate structure is studied by theory,finite element simulation and experiment.The influences of laying angle,material properties,layer number and moisture parameters are obtained,and the human elbow and knee are carried out under specific circumstances.The process was analyzed to study the potential application of variable stiffness multi-stable composite structures in human exoskeleton.The main research contents are as follows:1.Based on the classical laminate theory,the theoretical stable configuration of the variable stiffness multi-stable composite laminate structure is established,and the different stable configurations and stable mid-plane curves are predicted.The theoretical model shows that the first stable of the anti-symmetry/orthogonal/antisymmetry variable stiffness multi-stable composite laminate structure exhibits intermediate bending and flat state on both sides;the second stable is curved in the middle,but the direction of curvature is opposite to the first stable,the end also exhibits a curved state with the direction of curvature opposite the middle portion.The orthogonal/anti-symmetry/orthogonal variable stiffness multi-stable composite laminate structure has a first twist phenomenon on the left and right sides,and the curvature directions of the left and right sides are opposite to the curvature direction of the middle convex portion;the second stable is around.The sides are straight and twisted in the middle.2.In order to study the influence of characteristic parameters on the stable transition process of variable stiffness multi-stable composite laminate structure,the effects of laying angle,material properties,layer number and moisture were studied by finite element method.The results show that the load-displacement of the antisymmetry/orthogonal/anti-symmetry specimen is different from that of the orthogonal/anti-symmetry/orthogonal specimens,and the maximum load is reached through two different trends.The maximum load displacement of antisymmetry/orthogonal/anti-symmetry specimens is slightly larger than that of orthogonal/anti-symmetry/orthogonal specimens,but the corresponding displacement value is smaller than that of orthogonal/anti-symmetry/orthogonal specimens.In the anti-symmetry/orthogonal/anti-symmetry specimens,the displacement value of the specimens with smaller layers is larger than that of the specimens with more layers when they reach the second stable.With the increase of layers,the maximum load increases.The displacement of orthogonal/anti-symmetry/orthogonal specimens to the second stable increases with the increase of layers.Moisture has a significant effect on the maximum load of the anti-symmetry/orthogonal/anti-symmetry specimens,and as the moisture becomes larger,the maximum displacement decreases.Moisture does not affect the load-displacement trend of the orthogonal/anti-symmetry/orthogonal specimen during steady-state transition,but as the moisture changes,the maximum load and maximum displacement of the specimen become larger.3.Stable transformation experiments were carried out on the experimental specimens,and load-displacement curve was obtained.The experimental specimens with smooth and complete surface and stable state were prepared by hot-pressing cooling method.Through the experimental method,the load-displacement of variable stiffness multi-stable composite laminate structure during the stable transformation is obtained by using the modified testing platform of the tensile testing machine.The changing rules of the laying angle,material properties,layers number and moisture on the variable stiffness multi-stable composite laminate structures are verified.The maximum load and displacement of the anti-symmetry/orthogonal/anti-symmetry specimen is larger than that of the orthogonal/anti-symmetry/orthogonal specimen.Material properties will not change the load-displacement curve of the same laying angle.The load-displacement curves of variable stiffness multi-stable composite laminate structures are different with the layers number,and the rules of antisymmetry/orthogonal/anti-symmetry and orthogonal/anti-symmetry/orthogonal specimens are opposite.Moisture can change both the maximum load and the displacement at the second stable state.4.An initial exploratory study on the application of variable stiffness multi-stable composite laminate structure in human exoskeleton.When the elbows and knees are kept in a bent state,the specimen is in a stable configuration;when the elbows and knees are rotated through a certain angle to maintain the straight state,the specimen is in another stable configuration.Due to the fixed material properties,laying angle,layer number and moisture,the variable stiffness multi-stable composite laminate structures have a fixed shape in each stable.By measuring the angle of each specimen in the stable configurations,the applicability of the specimens in human exoskeleton is determined which shows the extensive application prospect of composite materials in human exoskeleton.更多还原