基于薄层单元的螺栓连接结构接触面不确定性参数识别

提出了一种螺栓连接接触面不确定性参数识别方法,首先采用薄层单元对接触面进行参数化,然后根据不确定性识别方法识别薄层单元参数。以四螺栓搭接结构试验模型为研究对象,开展接触面不确定性参数识别方法仿真研究。采用Monte-Carlo方法构造待识别参数真实值样本,代入基准有限元模型中计算获得具有统计意义的仿真试验数据;采用不确定性参数识别方法预测薄层单元参数均值与标准差,仿真结果表明：该方法能够较为准确的模拟接触面法向和切向接触刚度,并显著提高连接结构的建模效率,建立反映真实结构动态性能统计特征的有限元模型。     

基于各向同性本构关系薄层单元的螺栓连接参数识别

针对螺栓连接建模与参数识别问题开展研究。基于各向同性本构关系薄层单元理论,提出螺栓连接结构接触面力学性能识别方法。对单个螺栓搭接及多个螺栓搭接两种结构分别进行有限元建模,忽略螺栓质量、螺孔影响,搭接界面采用各向同性本构关系的薄层单元模拟。根据试验模态参数构造优化问题,识别搭接界面薄层单元材料参数。结果表明,两种螺栓连接结构前四阶弯曲模态频率计算精度较高,薄层单元能准确反映接触界面力学性能。该方法适用于单个螺栓及螺栓较密集工况动力学精确模拟。     

基于动力学模型修正的螺纹连接结构建模

在结构动力学仿真分析中,螺纹连接件的等效处理对分析精度和效率有直接影响。针对目前螺纹连接等效处理模型复杂、精度不足的问题,提出了一种基于动力学模型修正技术、以集中刚度单元替代螺纹连接件的等效建模方法。首先,应用所提出的建模方法,以L形螺钉连接板为对象,建立了螺纹连接系统等效模型,通过模态测试,研究了固有频率随拧紧力矩的变化规律;然后应用动力学模型修正技术,对建立的简化模型中刚度参数进行了修正。修正后的简化模型能够在较大拧紧力矩范围内,将固有频率计算误差控制在2.5%,表明所提出的方法是一种高效可行的螺纹连接简化方法。     

基于接触单元的复合材料螺栓连接结合部的动力学分析

用螺栓连接复合材料板是直升机结构中常见的固定方式。为了能够准确模拟复合材料螺栓连接结构的振动特性,该文采用基于接触单元的建模方法来模拟结合部的动力学特性,详细介绍了整个有限元的建模过程,包括定义单元类型、定义材料属性、单元网格的划分、边界条件以及确定接触分析、求解和后处理。该文还探讨了不同预紧力下复合材料板螺栓连接的固有频率。由试验结果可知,采用该文提出的建模方法可以准确模拟其动态特性。     

螺栓连接框架结构的有限元模型修正

综合运用有限元仿真、试验模态测试和模型修正技术,对一个由螺栓连接的三层框架结构进行了动力学特性分析和响应预测,并对其中涉及到的相关问题进行了讨论。首先,采用不同类型单元分别建立结构的实体有限元模型、板-梁有限元模型以及三自由度集中参数模型,并进行模态计算。然后,对实际结构进行模态测试,并将三类模型的计算结果与测试数据进行对比,分析不同类型单元所建立模型的异同以及由螺栓连接的复杂性、加工装配的误差和材料参数的不准确等不确定因素对建模及计算误差所造成的影响,从而确定合理的修正参数。接着,用模态测试数据对模型参数进行修正,使得修正后的模型能够准确反映实际结构的固有频率和振型。最后,将测试获取的阻尼参数加到修正后的模型上,进行冲击激励下的响应预测,并与实际结构的测试结果进行对比,取得了满意的结果。     

轴向预紧作用下的组合转子轴系模态特性研究

组合转子轴系结构是空天动力装备中发动机转子系统的主要结构,由于轴系中各部件接触面的存在使得转子系统动力学特性难以准确掌握,当涉及转子工作转速裕度时会产生一定的设计风险。针对组合转子轴系单主轴多部件轴向预紧结构特点,考虑转子不同接触面之间非线性连接参数,提出一种综合利用薄层单元和零长单元建模的两步模型修正方法,采用基于响应面优化的静态结构非线性分析以及基于随机统计学模型的粗糙表面接触分析进行薄层单元材料参数以及零长单元接触刚度系数识别,建立组合转子轴系动力学模型。根据某型发动机氢涡轮泵转子结构特点设计制造转子试件,对其自由模态进行试验研究,得到了不同螺纹预紧状态以及轴向预紧作用对组合转子轴系前两阶模态特性的影响。对比试验数据可知所提模型优化方法可以很好地反映出不同轴向预紧作用下组合转子轴系前两阶模态频率的变化趋势,在转子模态参数线性变化范围内计算误差小于1%,验证了该方法的正确性和有效性,为组合转子轴系精细化建模提供了参考依据。     

应用梯度连接层的层合电工钢梁螺栓结合部简化模型研究EI北大核心CSCD

表征电工钢片间螺栓结合部连接参数是进行铁心结构动力学分析的关键,针对现有变压器铁心动力学模型参数识别误差大的问题,提出了考虑螺栓结合面压强分布不均匀的梯度连接层模型。通过理论计算获得了螺栓结合部的压强分布,推导了梯度连接层弹性参数与螺栓结合部接触压强的关系式。在获得层合电工钢梁试件等效材料参数的基础上,对由螺栓连接的两根相同层合电工钢梁,建立了梯度连接层模型模拟层合电工钢梁之间的螺栓结合部。经模态对比修正了梯度连接层的弹性参数,修正后螺栓连接层合电工钢梁试验模态与计算模态的前8阶振型一致,对应固有频率的误差在1%以内,证明了梯度连接层模型的准确性。在变压器铁心中应用修正后的梯度连接层模型,能够提高建模精度。     

考虑螺栓球节点半刚性的网格结构有限元模型修正研究

为获取用于螺栓球节点网格结构健康监测准确有限元模型,用具有刚度可调节点单元描述节点半刚性;采用神经网络技术,利用有限测点模态信息构造网络输入参数CPFM,提出对螺栓球节点单元刚度折减系数进行分步修正新方法。以单层柱面网壳振动台试验模型为例,在螺栓球节点精细化模型基础上,基于实测模态数据对其进行有限元模型修正。结果表明,修正后有限元模型能较好反映该网壳结构的真实动力特性,采用分步修正算法能精简神经网络结构,可有效用于螺栓球节点网格结构有限元模型修正,具有一定实用价值。     

螺栓与孔间隙对单搭单螺栓连接板模态频率的影响

由于装配需要或者制造误差等因素的影响,连接板的螺栓与螺栓孔之间不可避免地存在间隙,而且间隙的变化对连接板的模态频率有一定的影响。通过研究螺栓与孔间隙对单搭单螺栓连接板模态频率的影响机制,讨论一种基于变通孔直径的螺栓连接动力学设计方法。首先,基于ABAQUS软件和Python语言,建立了包含变通孔直径的单搭单螺栓连接板有限元计算模型;然后,探讨了螺栓连接板在一端固支、两端固支两种边界条件下螺栓与孔间隙变化对连接板模态频率的影响机制;最后,提出了一种基于变通孔直径的螺栓连接板动力学设计方法。结果表明:当通孔直径为螺栓直径的1.02~1.20倍时,通孔直径的变化对螺栓连接板各阶固有频率的影响可忽略;通孔直径大于螺栓直径的1.21倍时,其变化对连接板模态频率有明显的影响,且影响程度各异。研究表明在特定激励环境下可通过改变通孔直径来改变系统模态频率,从而避免结构共振。该方法为螺栓与孔间隙对复杂螺栓连接系统固有频率的影响分析提供了参考,也为螺栓连接系统的抗振疲劳设计问题提供了思路。     

基于Iwan模型的螺栓连接结合面非线性等效模型

螺栓连接结构在机械装备中应用广泛,但进行螺栓连接结合面动力学建模时,大量的结合面接触单元会导致计算效率低等问题,因此建立其简化等效模型具有重要意义。针对螺栓连接结合面恢复力及位移的滞回特性,基于修正的离散Iwan模型,对滞回曲线离散化得到Iwan模型参数,在ANSYS中用COMBIN40、COMBIN14、MASS21单元建立其等效模型。验证等效模型在不同载荷下静力滞回特性,滞回曲线面积误差小于10%,相关性误差小于1%;对动态特性进行验证,冲击和简谐激励下的响应和接触模型吻合较好。研究结果表明,所建等效模型单元数量大幅减少,计算效率提高,可以用于复杂装配体的接触简化并计算动态响应。     

Experimental characterization of hybrid composite-to-metal bolted joints under flexural loading

Presented is an investigation of the structural performance of hybrid composite-to-metal bolted joints loaded in flexure. The main goal was to develop a watertight, hybrid connection to resist bending loads. The effect of bolt type, doubler plate geometry and foam inserts was studied. Fourteen different joint configurations were tested including standard bolted joints and bolted joints with doubler plates. The performance of connections loaded cyclically in flexure was assessed by comparing: (1) the initial damage and failure loads; (2) the types of failure modes; and (3) the joint initial rotational stiffness. Instability in the hysteresis loops, where the load drops in subsequent cycles, is used as an indication of damage. A joint using a short doubler plate, a foam insert, and a single row of bolts, was found to be at least 33% stronger and 29% stiffer when compared to a standard bolted joint with two rows of the same diameter bolts. Use of doubler plates and foam inserts in a bolted joint resulted in higher strength and stiffness and can effectively mitigate joint opening, which improves the ability to seal the joint and maintain watertight integrity.     

三维六向编织复合材料单剪搭接连接结构在拉伸载荷下的力学性能

通过试验测试与数值模拟相结合的方法对三维六向编织复合材料的螺栓连接性能进行了研究。首先,通过拉伸试验对不同侧向约束螺接方式连接件的连接强度进行了测试。测试结果表明:单搭连接结构的二次弯曲现象明显,连接强度与侧向约束有一定的关系,使用垫片可有效提高连接强度,螺栓拧紧力矩增加对连接强度影响不大;连接结构的破坏模式包括挤压破坏和拉伸破坏,在孔径较小时其主导破坏模式是挤压破坏。随后,基于测试中发现的破坏模式,建立了基于点应力准则的分析模型,并使用升温法实现螺栓拧紧力矩的施加。通过数值结果与试验结果的比较验证了分析模型的可靠性。最后,利用得到验证的分析模型,分析了单搭连接的二次弯曲现象,获得了侧向约束面积、螺栓拧紧力矩及连接平板厚度对单搭单螺栓连接结构力学性能的影响规律。分析结果表明:当侧向约束应力增加时,连接强度表现为先增加后降低的规律。     

螺栓节点板抗剪连接的有限元模拟方法研究

为了分析螺栓节点板抗剪连接的受力性能,采用常见的三种有限元方法进行模拟计算,比较不同方法的计算结果、建模难度和计算效率等,并将某简单实例的有限元分析结果与试验结果进行比较,最后给出有限元模拟方法的应用建议。研究表明：接触加预紧力是相对最为合理的一种方法,但该方法建模复杂、计算费时;其次是耦合螺孔节点方法,但该方法会在耦合节点处产生应力和位移的畸变;直接粘接方法的模拟效果最差,主要因为该方法将各块连接板粘接成一个整体参与受力,从而导致连接板处的计算结果偏小。     

钢管混凝土梁柱加强环螺栓节点受力性能优化研究

为研究具有不同构造形式的加强环螺栓连接节点的力学性能,基于圆钢管混凝土柱-钢梁外加强环螺栓连接节点单调加载试验结果,采用合适的混凝土与钢材本构模型,通过ABAQUS建立该类节点的三维精细化有限元分析模型;对比分析试验和模型的受力特征和破坏形式,验证了数值模型的可靠性;与加强环焊接刚接节点对比,通过对不同构造措施下的加强环螺栓连接节点进行数值模拟,分析结果表明：加强环上采用4排螺栓并加设腹板加劲肋和环板加劲肋的加强环螺栓连接节点可达到全焊加强环刚接节点的初始刚度和抗弯承载力。     

Effects of various parameters on dynamic characteristics in adhesively bonded joints

Adhesively bonded lap joints are used extensively in various industries. Some disadvantages like holes, thermal effects occurring in the bolted, welded, riveted, and soldered joints are not in question in adhesively bonded joints. Strong adhesive materials used in bonding have been greatly developed in recent years, and then the properties of lightness, sealing, corrosion resistance, heat and sound isolation, damping, and quickly mounting facility have been highly improved. In this work, effects of various dynamic characteristics in the adhesively bonded joints subjected to dynamic forces are investigated using the finite element method. The investigation is conducted on a three-dimensional model. The finite element model of the joint is obtained using isoparametric three-dimensional elements having eight nodes with three degrees of freedom each. Mesh generation is accomplished automatically in a computer.The joint is modeled as a thin plate clamped from the left side. The in-plane vibration analysis is constructed. First, the natural frequencies and mode shapes are obtained, and then point and transfer receptances are extracted, employing structural damping. It is observed that the damping greatly decreased the resonance amplitudes.     

Thermal preconditioning study for bolted tension joints in pultruded GRP plate

Thermocouples have been used to monitor the time versus temperature rise response at the centre of four sizes of pultruded GRP plate used in bolted tension joints in order to demonstrate that all of the GRP plate is at the required temperature prior to testing the joints to failure. A simple one-dimensional finite element (FE) model has also been developed and used to predict time versus temperature rise response. The experimental and numerical results confirm that a thermal preconditioning period of 30 min duration is more than adequate for all of the pultruded GRP plates to achieve the actual test temperatures of 40, 60 and 80 °C.     

A novel predictive model for mechanical behavior of single-lap GFRP composite bolted joint under static and dynamic loading

Mechanical connection of composite is critical due to its complicated meso-structure and failure mode, which has become a bottleneck on reliability of composite material and structure. Although many researches on composite bolted joints have been carried out, the theory and experiment on mechanical behavior of such a joint structure under dynamic loading were rarely reported. Here, we propose a novel predictive model for quasi-static and dynamic stiffness of composite bolted joint by introducing the strain rate dependent elastic modulus into the mass spring model. Combined with the composite laminate theory and Tsai-Hill theory, the present model was capable of predicting the strain rate dependent stiffness and strength of the composite bolted joint. Quasi-static and impact loading experiments were carried out by Zwick universal hydraulic testing machine and split Hopkinson tension bar, respectively. The stiffness and strength predicted by our model showed good accordance with the experiment data with errors below 12% under quasi-static loading and below 30% under impact loading. The results indicated that under impact loading, stiffness and strength of the composite bolted joint were significantly higher than their quasi-static counterparts, while the failure mode of the joint structure trended towards localization which was mainly bearing failure. Among various lay-up ratios studied, the optimal lay-up ratio for quasi-static and dynamic stiffness was 0:±45:90 = 3:1:1.