蜂窝夹层木质复合材横向承载力学特性研究

发布时间：2018-04-09 06:14

本文选题：夹层结构　切入点：木质面板　出处：《中南林业科技大学》2017年博士论文

【摘要】：蜂窝夹层木质复合材由于等效密度低、制造的便利性、力学的复合效应、可设计性及平整度高等优点在家具产品、室内装饰、包装运输等民用领域具有广泛应用前景。研究该种复合结构材在横向承载下的力学特性,为产品优化设计与工程应用提供理论基础,意义重大。本文以蜂窝夹层木质复合材为研究对象,系统研究了横向载荷作用下夹层梁的弯曲性能及夹层板的平压性能,结论如下:(1)推导出了基于等效单层梁理论计算软夹芯夹层梁最大弯曲正应力的公式。运用正交试验法进行蜂窝夹层梁三点弯曲试验,结果表明:蜂窝边长对静曲强度的影响极其显著,表板类型、涂胶量对静曲强度的影响不显著;芯层厚度对“//”方向试件静曲强度的影响显著,而对“⊥”方向试件影响极其显著。“⊥”方向试件的静曲强度值均高于“//”方向试件。在Winkle弹性地基梁理论的基础上,考虑了表板弯曲正应力对局部凹陷的影响,推导出软夹芯夹层梁三点弯曲试验表面压溃载荷的计算公式。系统分析了芯层剪切失效与表面压溃二种弯曲破坏模式,并将理论模型与试验数据进行对比分析,相对误差约±20%以内。(2)建立了基于二变量的夹层梁弯曲变形的分层一阶剪切理论。该理论与三点弯曲试验结果、传统一阶剪切理论的对比分析,结果表明:小弹性变形范围内,分层一阶剪切理论比传统一阶剪切理论预测的跨中挠度值保守。在同样的受力条件下,“//”方向试件跨中挠度均大于“⊥”方向试件。分层一阶剪切理论计算的芯层切应变与切应力值比传统一阶剪切理论低,但随着芯层厚度的增加,二种理论的计算差异逐渐变小。将分层一阶剪切理论计算的切应力在横截面积分,其剪力值满足于静力平衡条件。(3)在分层一阶剪切理论的基础上,建立了二节点六自由度的有限元梁单元模型。数值分析结果表明:小弹性变形范围内,有限元模型与分层一阶剪切理论计算的跨中挠度十分接近,平均差异小于10%。当芯层厚度较小时,有限元模型计算的横截面切应变与切应力接近于分层一阶剪切理论;随着芯层厚度的增加,其值逐渐靠近传统一阶剪切理论。(4)在传统一阶剪切理论的基础上,修正了夹层梁横截面切应力值和芯层剪切模量,建立了修正一阶剪切理论。数值分析结果表明:当芯层厚度较小时,修正一阶剪切理论与分层一阶剪切理论计算的跨中挠度十分接近;当芯层厚度增加时,修正一阶剪切理论的模型预测值逐渐介于分层一阶剪切理论与传统一阶剪切理论之间;同时,剪切挠度、因弯矩引起的挠度随之减小,但剪切挠度占总挠度的比重越来越大。另外,当芯层厚度增加时,修正一阶剪切理论与传统一阶剪切理论计算的剪切挠度值趋于一致。(5)在三点弯曲试验的基础上,推导出考虑上表板弯曲正应力的表面压痕位移计算公式。对比试验数据,考虑压痕分层一阶剪切理论与考虑压痕修正一阶剪切理论的跨中挠度预测精度好于传统一阶剪切理论。(6)运用正交试验法进行蜂窝夹层板平压性能试验,结果表明:蜂窝边长对芯层横向弹性模量和平压强度的影响极其显著,涂胶量对芯层横向弹性模量和平压强度的影响较显著,表板类型、芯层厚度对芯层横向弹性模量和平压强度的影响不显著。在平压强度试验的基础上,推导出基于Timoshenko薄板稳定理论的夹层板受压等效临界屈曲应力的计算公式,并与试验数据进行对比,相对误差约±15%以内。在芯层蜂窝材料选定的情况下,增加胞元壁厚和减小胞元的边长能有效增强蜂窝夹层板的抗压性能。
[Abstract]:Honeycomb sandwich wood composites due to the equivalent of low density, convenient manufacturing, composite effect of mechanical design, and the flatness of the advantages in furniture, interior decoration, and has wide application prospect in civil field of packaging and transportation. The study on the mechanical properties of the composite material in the structure under the lateral load, and provide a theoretical basis for. Product optimization design and engineering application of great significance. This paper honeycomb sandwich wood composites as the research object, the bending properties of sandwich beam under transverse loading and flat sandwich compression performance of the system, the research conclusions are as follows: (1) derived the soft sandwich beam of maximum bending stress calculation based on the theory of equivalent single beam the formula. Using the orthogonal testing method of honeycomb sandwich three-point bending test, the results show that the influence of the edge length of static bending strength is extremely significant, table board type, amount of glue on the static bending strength No significant influence; the core layer thickness on the "/ /" direction effect of static bending strength and a significant, on the "t" direction of specimen effect is extremely significant. "An" direction of specimen mor values were higher than the "/ /" direction of specimen. Based on Winkle elastic foundation beam theory, considering the the table plate bending stress influence on local depression, calculation formula of soft sandwich three-point bending test surface crushing load. The system analyzes the core shear failure and surface collapse two bending failure mode, and the theoretical model and the experimental data were analyzed, the relative error is about 20%.. (2) established a layered bending deformation of the beam dissection in two variables based on the first-order shear deformation theory. The theory and three point bending test results, analysis, comparing with the traditional first-order shearing theory shows that the small elastic deformation range, a hierarchical order shear theory than. Unified prediction order shear theory deflection value. In the conservative force under the same conditions, "/ /" direction of specimen deflection are greater than the "t" direction of specimen. The core layer calculation of layered first-order shearing theory of shear strain and shear stress values than conventional first-order shearing theory is low, but with the increase the thickness of core layer, calculate the difference between the two theories gradually become smaller. The calculation of layered first-order shear deformation theory of the shear stress in the cross section of the shear integral value satisfies in static equilibrium conditions. (3) based on a hierarchical order shear deformation theory, a finite element beam element model of six degree of freedom two nodes. The numerical results show that the small range of elastic deformation, finite element model and a hierarchical order shear theory calculation of deflection is very close, the average difference is less than 10%. when the core layer thickness is small, the cross section calculation of finite element model of shear strain and shear stress is close to A hierarchical order shear theory; with the increase of the thickness of core layer, its value is gradually close to the traditional first order shear theory. (4) based on the traditional first-order shearing theory, modified sandwich beam cross section of shear stress and shear modulus of core layer, a modified first order shear deformation theory and numerical analysis results. Show that: when the core layer thickness is small, modified first order shear deformation theory and layered first-order shear deformation theory calculated deflection is very close; when the core layer thickness increases, forecast the first-order shear deformation theory model gradually between layered unified first-order shear deformation theory and order shear theory; at the same time, shear deflection due to the deflection caused by the bending moment, shear deflection decreases, but the increasing proportion of the total deflection is larger. In addition, when the core layer thickness increases, the shear deflection correction calculation of the first-order shear deformation theory and the traditional first-order shearing theory value tends to be consistent. (5) in three point bending Based on the test of curved surface indentation displacement is derived, the table plate bending stress formula. Compared with experimental data, and considering the deflection prediction accuracy of indentation modified first-order shearing theory is better than the traditional first-order shear deformation theory considering indentation layered first-order shear deformation theory. (6) by using orthogonal test method the honeycomb sandwich plate flat compression test, the results show that the influence of the edge length of the transverse elastic modulus of compressive strength of core layer and the effect is extremely significant, amount of glue on the transverse elastic modulus and compressive strength of the core layer and significantly, table board type, core layer thickness on the transverse elastic modulus of the core layer of peace pressure strength is not significant based on the compressive strength test, stress calculation formula of the critical buckling pressure equivalent sandwich plate Timoshenko plate based on stability theory is derived, and compared with the experimental data, the relative error less than about 15%. In the selected core layer of honeycomb material under the condition of increased cell wall thickness and length reduction swelling element can effectively enhance the compression performance of honeycomb sandwich plates.

【学位授予单位】：中南林业科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB33

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