湿热环境下平纹编织面板蜂窝夹芯板的渐进损伤分析

为了研究侧向压缩载荷下单侧面板含穿孔的平纹编织面板蜂窝夹芯板的损伤行为,建立考虑湿热效应的渐进损伤模型.编写UMAT子程序将考虑湿热效应的本构关系、温度变化对材料属性的影响、选用的失效准则和刚度退化模型加入到考虑湿热效应的渐进损伤分析中.将模型在25℃、0吸湿量条件下预测的位移-载荷曲线及失效形式与实验进行对照,以验证建立模型的正确性.进一步在5个温度和5个湿度下研究湿热效应对受侧向压缩载荷的蜂窝夹芯板承载强度的影响.结果表明,建立的模型可有效预测损伤的扩展过程和湿热环境对蜂窝板性能的影响,随着温度和湿度的增加,蜂窝板的承载强度逐渐下降.     

蜂窝铝夹芯板结构三点弯曲力学特性有限元仿真分析

结构轻量化是航空航天、车辆、船舶等领域发展的永恒主题,蜂窝铝夹芯板是轻量化结构中的重要组成部分。该文建立了蜂窝铝夹芯板三点弯曲有限元模型,通过三点弯曲有限元仿真分析来研究蜂窝铝夹芯板结构的力学性能;同时分析了不同面板厚度和不同芯层厚度对结构极限载荷的影响。结果表明,蜂窝铝夹芯板结构的极限承载能力与面板厚度和芯层厚度均呈现正相关关系,且芯层厚度的变化对极限载荷的影响较大。所得研究结果和结论为蜂窝铝夹芯板结构的工程应用提供参考依据。     

蜂窝铝夹芯板动态冲击试验研究

采用落锤低速冲击试验测试蜂窝铝夹芯板的动态力学性能,研究了其破坏形态、破坏过程和典型荷载-位移曲线,分析了冲击速度和面板厚度两个因素对夹芯板极限冲击承载力和吸能量的影响,并和准静态试验下相应面板厚度的夹芯板进行力学性能对比。试验结果表明,蜂窝铝夹芯板的典型冲击荷载-位移曲线呈现出五个主要阶段,在不同冲击速度下夹芯板的极限冲击承载力和吸能量基本一致,而随着面板厚度的增加,夹芯板的极限冲击承载力和吸能量随之增加,三种不同面板厚度的夹芯板在落锤低速冲击作用下的极限冲击承载力和吸能量比在准静态作用下提高。     

蜂窝铝夹芯板准静态局压试验研究

通过准静态试验测试了蜂窝铝夹芯板的局压力学性能,分析了其破坏过程、破坏形态和典型荷载-位移曲线,研究了面层厚度、孔棱大小、压头类型、边界条件等因素对其极限荷载和吸能能力的影响。结果表明,蜂窝铝夹芯板局压荷载-位移曲线表现两种典型类型,呈现出弹性阶段、局部损伤阶段、强化阶段、整体损伤阶段、压缩致密阶段、底部破坏阶段等六个主要阶段。面层厚度和孔棱大小对夹芯板局压承载力和吸能能力有一定影响,压头类型对局压承载力和刚度有较大影响,但对吸能能力影响不大,边界条件和试件厚度对夹芯板强度和吸能能力影响不大。     

湿热环境下含脱粘损伤蜂窝夹芯材料弯曲性能研究

通过使用三明治夹芯等效理论将蜂窝芯层等效为均匀连续的实体单元,将湿热环境中的湿应力等效为热应力,建立湿热环境下的蜂窝夹芯材料本构方程,以改进Hashin准则与Besant准则作为蜂窝夹芯材料的失效判据,并通过编写VUMAT子程序实现.采用Cohesive单元模拟面板与芯层间的连接方式建立湿热环境下蜂窝夹芯板的有限元模型...     

蜂窝夹芯板参数化建模与优化设计

在蜂窝夹芯板的有限元分析过程中,为提高结构的建模和分析效率,基于有限元软件开发参数化建模与分析模块,可以完整地进行蜂窝结构的建模、分析、校核与后处理,使蜂窝结构的有限元分析过程流程化、高效化.在此基础上,以质量轻量化为目标,以结构强度为约束条件,基于MATLAB使用遗传算法、罚函数法、模式搜索法对蜂窝结构进行尺寸参数优...     

铝蜂窝夹芯板低速动态冲击响应研究

为研究不同结构参数对质量相同、强度不同的两种铝蜂窝夹芯板低速动态冲击响应的影响,建立了铝蜂窝夹芯板受半球型落锤低速冲击的数值模型,并将有限元计算结果与试验结果进行对比,检验了模型的可靠性。在此基础上,对比研究了不同上下铝板厚度和不同蜂窝芯壁厚对两种铝蜂窝夹芯板在低速冲击下吸能效果的影响。结果表明：在质量相同的情况下,强度小、高度大的夹芯板在低速冲击下力-位移曲线更易出现双峰模式,增加蜂窝芯壁厚或是上下铝板厚度都会使第一次的峰值力增加,第二次峰值力降低;强度小、高度大的夹芯板蜂窝芯在低速冲击中吸能占比更多,强度大、高度小的则是上层铝板吸收的能量更多,前者的质量、体积比吸能更高;铝蜂窝夹芯板质量比吸能和体积比吸能与壁厚边长比、板厚芯高比均呈幂次关系。     

复合材料蜂窝夹芯结构的三点弯曲性能

通过三点弯曲试验研究了纤维增强复合材料铝蜂窝夹芯结构的力学性能。分析了不同面板类型(碳纤维面板、玻璃纤维面板、碳纤维/玻璃纤维面板)以及面板厚度和芯体孔径大小对结构破坏模式、极限载荷和能量吸收的影响。结果表明,碳纤维/铝蜂窝夹芯结构相较于其他两种结构,其极限载荷和能量吸收更强;面板越厚,芯体孔径越小,结构的极限载荷和能量吸收越强;面板厚度对于能量吸收影响较大,芯体孔径对极限载荷影响较大。对碳纤维/铝蜂窝夹芯结构进行有限元模拟,对其破坏变形过程进行对比分析后,验证了模型的有效性,为试验的设计和分析提供了指导与帮助。     

直升机尾梁蜂窝夹层结构四点弯曲试验

对民用直升机尾梁蜂窝夹层结构进行了弯曲加载试验,应用四点弯曲的加载方式分析考核区的纯弯曲性能.设计了一种试验件的加强方式以防止加载区提前发生破坏,并对某型直升机尾梁封边框处使用不同胶膜的蜂窝夹层结构进行切割和修理来制备试验件,通过试验对直升机尾梁蜂窝区的界面连接强度与45°封边框处使用不同胶膜的相关性进行了分析.对比分...     

铝蜂窝夹芯板受爆炸载荷时的动力响应

在对爆炸载荷下铝蜂窝夹芯板的变形机理和失效模式研究的基础上,文中试图建立铝蜂窝夹芯板的刚塑性动力分析模型。首先给出考虑芯层强度的拉—弯联合作用的屈服条件,考虑到冲击载荷作用时间相对于芯层的压缩和夹芯板的整体动力响应时间要短的多,应用修正的哈密尔顿原理,得到固支边界条件下受爆炸载荷作用的夹芯方板三阶段变形的塑性动力响应,得出其表达式。并与实验结果进行比较和分析,研究表明在考虑有限变形情况下,文中的分析结果和实验结果吻合较好。     

The response of honeycomb sandwich panels under low-velocity impact loading

This paper describes the results of an experimental investigation and a numerical simulation on the impact damage on a range of sandwich panels. The test panels are representative of the composite sandwich structure of the engine nacelle Fan Cowl Doors of a large commercial aircraft. The low-velocity impact response of the composites sandwich panels is studied at five energy levels, ranging from 5 to 20 J, with the intention of investigating damage initiation, damage propagation, and failure mechanisms. These impact energy levels are typically causing barely visible impact damage (BVID) in the impacted composite facesheet.A numerical simulation was performed using LS-DYNA3D transient dynamic finite element analysis code for calculating contact forces during impact along with a failure analysis for predicting the threshold of impact damage and initiation of delaminations. Good agreement was obtained between numerical and experimental results. In particular, the numerical simulation was able to predict the extent of impact damage and impact energy absorbed by the structure. The results of this study is proving that a correct numerical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design a more efficient impact-resistant aircraft structure.     

The three-point bending of Y-frame and corrugated core sandwich beams

Sandwich beams comprising Y-frame and corrugated cores have been manufactured by assembling and brazing together pre-folded AISI type 304 stainless steel sheets. The longitudinal axis of the cores coincides with the axis of the beams. The quasi-static three-point bending response of both simply supported and clamped beams is measured along with the indentation response of the beams placed on a rigid foundation. The investigation reveals that the initial collapse strength of the beams is governed by the indentation of the Y-frame or corrugated core for all beam geometries considered here. The simply supported beams have a softening response beyond the initial peak load while the clamped beams display a hardening response due to the longitudinal stretching of the face-sheets. The experimental investigation reveals that sandwich beams with Y-frame or corrugated cores have comparable responses for each of the loading situations considered. Additional insight into the deformation modes is obtained by three-dimensional finite element (FE) calculations.     

Dynamic response of aluminum honeycomb sandwich panels subjected to hypervelocity impact by porous volcanic rock projectile

The dynamic response and damage behavior of aluminum honeycomb sandwich panels (HC/SPs) subjected to hypervelocity impact by volcanic rock projectiles were investigated by hypervelocity impact tests and hydrocode simulations. The experiments were conducted using a two stage light gas gun and the results showed that the failure modes in HC/SPs subjected to hypervelocity impact by volcanic rock projectiles mainly took forms of front-face denting and circular perforation, honeycomb core collapsing and rapture, rear-face petal-ling and perforation etc. A 3D discrete configuration of the porous volcanic rock projectiles was set up. The hypervelocity impact behavior of the HC/SPs was investigated through hydrocode modeling, within a Lagrange-SPH coupling method in LS-DYNA solver. It was found that the dynamic response and failure modes in the HC/SPs were significantly influenced by the impact location and the impact velocity of the volcanic rock projectile.

     

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.     

3D elasticity analysis of sandwich panels with graded core under distributed and concentrated loadings

Sandwich panels are a type of panel offering weight savings over standard single layer panels, whilst remaining both strong and stiff. However, due to the mismatch of properties between the face sheets and the core, stress concentrations can occur at the face sheet/core interfaces, often leading to delamination. One possible solution to this problem is the introduction of a functionally graded core—a core in which the properties vary gradually from the face sheets to the centre, eliminating any abrupt changes in properties. This paper presents a three-dimensional elasticity analysis for a sandwich panel with stiffness of the core graded in the thickness direction, on the basis of the recently developed 3D elasticity solution. A comparative study of panels with homogeneous and functionally graded cores is carried out to examine the effect of introducing a graded core on the stress and displacement fields under five different loading configurations (uniformly distributed, patch, point, hydrostatic and line).     

Effect of continuously grading fiber orientation face sheets on vibration of sandwich panels with FGM core

The main purpose of this paper is to investigate effect of continuously grading fiber orientation face sheets on free vibration of sandwich panels with functionally graded core using generalized power-law distribution. The benefit of using generalized power-law distribution is to illustrate and present useful results arising from symmetric, asymmetric and classic profiles. The fiber-reinforced composite material studied in the present work consists of silicon carbide fibers embedded in titanium matrix with the fiber volume fraction and fiber orientation graded in the radial direction. The face sheets have variation of the fiber orientation while the core has variation of fiber volume fraction. Generalized differential quadrature (GDQ) method is used to yield natural frequencies of the simply supported functionally graded sandwich (FGSW) panels on the basis of the 2-D, linear and small strain elasticity theory. The fast rate of convergence of the method is demonstrated and comparison studies are carried out to establish its very high accuracy and versatility. In this research work, a detailed parametric study is carried out to highlight the influences of continuously grading fiber orientation face sheets and different profile of fiber volume fraction and fiber orientation on the vibration characteristics of the FGSW panels.     

Experimental determination of elastic properties of the core in a thin sandwich plate with a metallic truss core

The deformation behavior and stress-strain relationships for a lightweight sandwich plate in the elastic regions are mainly dependent on the elastic properties of the core in the sandwich plate. The aim of this paper is to determine experimentally the elastic properties of a core in a thin sandwich plate with a metallic truss core. Three-points bending experiments were performed to obtain a linear relationship between compliance per span length and the square of the span length for the designed sandwich plate. The specimen was manufactured from the continuous multi-points resistance welding of SUS 3O4H sheets and crimped metallic truss cores. The elastic and shear moduli of the core were estimated by the slopes and the intercepts of the linear relationship, respectively. Through the comparison of the shear moduli and force-deflection considering the core stiffness with those disregarding the core stiffness, it was shown that the core stiffness should be considered to estimate accurately the elastic and shear moduli of a core as well as the force-deflection curves of a thin sandwich plate with a metallic truss core. The contribution ratios of the bending and shear deflections of the thin sandwich plate to the total deflection were investigated. In addition, the influence of the crimping angle on the elastic properties, the force-deflection curves, and the contribution ratios of both bending and shear deflections to the total deflection was examined.     

Analyses and preliminary tests of a balsa sandwich core with improved shear properties

End grain balsa is a common core material in sandwich structures. The main properties of interest of a sandwich core, in particular for marine applications, are the shear stiffness and shear strength. The end grain arrangement does not fully utilize the anisotropy of balsa wood for the benefit of shear properties. A new arrangement of balsa blocks in a sandwich core was developed and numerically analyzed. This new core, which consisted of an assembly of oddly shaped balsa blocks, allowed the grains in various balsa blocks to be oriented for example at 45° to the normal of the core. The effective out-of-plane shear stiffness was isotropic. Numerical analyses predicted a superior shear stiffness, which was confirmed by preliminary tests.     

Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part II: experimental investigation and numerical modelling

This study focuses on the competing collapse mechanisms for simply supported sandwich beams with composite faces and a PVC foam core subjected to three point bending. The faces comprise Hexcel Fibredux 7781-914G woven glass fibre-epoxy prepreg, while the core comprises closed cell Divinycell PVC foam of relative density 6.6% and 13.3%. The mechanical properties of the face sheets and core are measured independently. Depending upon the geometry of the beam and the relative properties of the constituents, collapse is by core shear, face sheet microbuckling or by indentation beneath the middle loading roller. A systematic series of experiments and finite element simulations have been performed in order to assess the accuracy of simple analytic expressions for the strength. In general, the analytic expressions for peak load are adequate; however, simple beam theory becomes inappropriate and the analytic models are inaccurate for stubby beams with thick faces relative to the core thickness. A failure mechanism map is constructed to reveal the dependence of the dominant collapse mechanism upon the geometry of the beam.     

Experimental study of honeycomb regenerator system for oxy-fuel combustion

An experimental study of a honeycomb regenerator for oxy-fuel combustion has been performed. A laboratory-scale test rig is set up and various experimental parameters such as cell density and length of the honeycomb regenerator, switching time, and bypass effect are investigated. The typical temperature trend of the heating and regenerating process is obtained for the oxy-fuel combustion. The regenerative characteristics for various combinations of these parameters are shown. It is found that part of the exhaust gas should be bypassed to use waste heat more efficiently and to optimize the efficiency of the honeycomb regenerator system for oxy-fuel combustion.