关键词： Multiobjective optimization  

摘要： In order to synergistically improve the crashworthiness safety and lightweight level of the oar body, a novel functionally-graded variable section double-hexagonal crash box was designed and proposed. The substructure at its lower end with regulär shape, namely functionally-graded variable section double-hexagonal tube (FS-DHT), was extracted as research subject, on which parametric geometric modeling was conducted. The finite element model of FS-DHT under axial crushing was established and verified by experiments. A comparative study concerning crashworthiness and energy absorption characteristics under axial crushing was conducted among FS-DHT, traditional straight DHT (S-DHT) and conical DHT (C-DHT). The influence of the tube wall thickness, the circumcircle radius differences at upper and lower end face of inner and outer hexagonal tubes, and the gradient exponent on the crashworthiness and energy absorption characteristics of FS-DHT under axial crushing was explored. A multi-objective optimization was carried out on FS-DHT by combining the optimal Latin hypercube sampling, response surface Surrogate model and the second-generation non-dominating sorting genetic algorithm, then verified. The finite element model of " bumper-crash box" assembly under axial crushingwas further established to verify the improvement effect of FS-DHT optimization on the crashworthiness of functionally-graded variable section double-hexagonal crash box. The results show that after optimization of FS-DHT, its specific energy absorption (SEA) increases by 21. 61% while its initial peak crushing force (IPCF) decreases by 13.40%, which meanwhile promotes the energy absorption (EA) of functionally-graded variable section double-hexagonal crash box to increase by 17. 14% and the corresponding IPCF at the bumper to decrease by 6. 46%, indicating a good multi-objective collaborative crashworthiness optimization is obtained. An effective novel structure and new approach are provided for synerg

关键词： 负泊松比   双材料胞元   梯度结构   失效变形模式   能量吸收   斜向加载  

摘要： 本文提出了基于曲边内凹双材料胞元的梯度负泊松比蜂窝结构,通过改变横纵向曲杆材料,设计了正梯度、负梯度、对称正梯度和对称负梯度四种材料递变泊松比梯度蜂窝结构.利用数值方法研究了各梯度结构的面内斜向冲击载荷作用时的动力学性能.研究发现,在斜向碰撞时下负梯度双材料排列模式的蜂窝结构吸能效果最好.针对负梯度双材料蜂窝结构,具体讨论了在不同冲击速度和冲击倾斜角度时的压溃变形模式、名义应力应变曲线与能量吸收效果的变化规律.结果表明,冲击速度和冲击倾斜角度对模式吸能效果的影响非常大;无论在何种速度下,倾斜角度越小,结构的吸能效果越好,即结构的耐撞性随碰撞倾斜角度的增大而减小.

关键词： 吸能盒   非线性有限元   双变梯度   耐撞性能   变形模式  

摘要： 为了提升车辆吸能盒的耐撞性,设计了厚度梯度、材料梯度及材料厚度双梯度变化的吸能盒。建立了吸能盒的有限元模型,采用非线性动力学有限元分析软件LS-DYNA进行仿真分析,并通过试验验证了有限元模型的可靠性。结果表明:厚度对耐撞性的影响较大。与匀质吸能盒相比,最优的厚度梯度吸能盒的比吸能(SEA)提高了53.37%,而其初始峰值力(PCF)仅增大了4.08%。提出两种双变梯度吸能盒,与匀质吸能盒相比,最优双变梯度吸能盒的SEA值提升了143.18%,但是其PCF值仅仅增大了3.9%。

关键词： 点阵材料   能量吸收   数值模拟   梯度结构   优化设计  

摘要： 提出了一种新型的余弦函数胞元基(Cosine function cell-based,CFCB)点阵材料,并对其面外压缩载荷下的力学性能开展试验及仿真研究,试验结果表明新型CFCB点阵材料在准静态面外压缩载荷下的能量吸收较相同质量的体心立方(Body centered cubic,BCC)点阵材料提升了134.4%;此外,通过有限元仿真发现CFCB点阵材料的能量吸收随胞元单杆直径增加而增加。为了进一步改善均匀型CFCB点阵材料的面外压缩变形模式并提高其承载性能,设计了一种层间梯度CFCB点阵构型,并结合试验与仿真手段探究了梯度CFCB点阵材料在准静态面外压缩载荷下的能量吸收特性及关键参数对其吸能特性的影响规律。结果表明:与均匀CFCB点阵材料相比,梯度CFCB点阵材料在吸能方面具有更强的优势,且增大梯度系数可以提高层间梯度点阵材料的承载能力与能量吸收能力。最后,采用离散变量多目标优化方法对层间梯度CFCB点阵材料进行了优化设计,优化后的梯度CFCB点阵材料的比吸能提高了35.3%,能量吸收增加7.1%。研究能够对新型CFCB点阵材料及其梯度构型设计提供可靠的试验结果、准确的数值模型及高效的优化方法。

关键词： 吸能盒   功能梯度结构   仿生截面   结构设计   多目标优化  

摘要： 传统的吸能盒结构,碰撞过程无法实现稳定有序折叠溃缩,同时存在单位质量吸能效果差的缺点,限制了汽车安全性能的提高。引入一种功能梯度材料(Functionally Graded Material,FGM)结构吸能盒,即在传统316L不锈钢基体上添加铝合金成分形成梯度材料结构,同时仿照竹节虫胫骨截面结构对其横截面形状进行优化,并基于优化拉丁超立方体试验设计和响应面模型对竹节虫胫骨横截面的具体结构进行多目标优化。仿真结果表明,优化后的仿生功能梯度材料吸能盒能够实现稳定的从头部至尾部的折叠溃缩。和传统吸能盒相比,仿生结构功能梯度吸能盒单位质量吸能效果提升,能够有效削弱碰撞对车身的损伤。

关键词： 梯度功能柱胞   吸能材料   准静态压缩   变形规律   吸能性能  

摘要： 通过万能试验机对梯度功能柱胞吸能材料进行了准静态压缩试验,研究了材料种类梯度配置、赤道半径梯度配置、极半径梯度配置、壁厚梯度配置4种不同芯层配置方式对梯度功能柱胞吸能材料变形规律和吸能性能的影响。结果表明,试样的变形吸能性能在压缩过程的前期主要受上层柱胞影响,后期主要受下层柱胞影响。均质柱胞吸能材料的上下层柱胞在整个变形过程差异较小,而梯度功能柱胞吸能材料都具有逐层变形、渐进吸能的特点。在准静态压缩荷载作用下,压缩80%的情况下,由于所有试样的变形程度均较为充分,此时试样的吸能量主要受压溃力指标影响,压溃力指标越高,吸能量越高;反之,压溃力指标较小时,位移越大的试样,吸能量越高。

关键词： 折纸结构   薄壁管   梯度泡沫填充   吸能特性   多目标优化  

摘要： 随着汽车工业的快速发展,我国车辆保有量持续激增。由此引发的交通安全事故也日益凸显,汽车安全问题愈发严重。为降低因车辆发生事故后的伤亡和损失,汽车被动安全设计显得尤为重要,传统汽车吸能结构以金属单胞薄壁管为主,存在吸能效率低,峰值载荷力较大、载荷稳定性差等缺陷。近年来,将折纸图案引入薄壁结构设计,通过预折痕控制压溃变形模式,以此改善其吸能特性,具有较大的应用潜力。同时,聚氨酯泡沫具有密度低、质量轻、吸能效果好等优点,是理想的吸能填充材料。 本文针对梯度泡沫填充的折纸型薄壁方管吸能特性及优化设计进行研究。确定了折纸型填充管的折纸图案和几何模型。利用3D打印技术成功制作试验样件,并对其进行轴向准静态压缩实验,对比分析折纸型填充管层数、层间二面角、壁厚和不同密度泡沫填充对结构吸能特性的影响规律。研究结果表明:引入折痕设计能够有效改善吸能结构的吸能特性,初始峰值力PCF显著降低,同时总吸能E A仍处于较高水平。折纸型填充管采用正梯度泡沫填充方式,其吸能能力优于负梯度和单一密度泡沫填充方式。最后,针对折纸型填充管进行多目标优化设计,建立代理模型预测层间二面角、层数以及填充不同密度的泡沫与模型的相关性。分别采用NSGA-II算法与CHC算法进行多目标优化求解分析,并通过仿真和试验对比验证优化后结构参数的准确性。结果表明,CHC算法较NSGA-II算法的优化结果更为准确。优化后的最优参数解为:层间二面角度数为150°,折纸管层数为8层,填充泡沫密度为0.3g/cm3。对应的折纸型填充管其比吸能SEA较普通直管提升10.3%,初始峰值载荷PCF下降47.4%。 综上所述,本文结果表明带有折纸图案设计和泡沫填充的折纸型填充管具有优良的吸能特性,这一研究可为后续引入更复杂的折纸图案设计和工程化实际应用提供研究思路和参考价值。

关键词： additive manufacturing   lattice structure   triply periodic minimal surface   energy absorption   sound absorption  

摘要： Lattice structures have drawn much attention in engineering applications due to their lightweight and multi-functional *** this work,a mathematical design approach for functionally graded(FG)and helicoidal lattice structures with triply periodic minimal surfaces is *** types of lattice structures including uniform,helicoidal,FG,and combined FG and helicoidal are fabricated by the additive manufacturing *** deformation behaviors,mechanical properties,energy absorption,and acoustic properties of lattice samples are thoroughly *** load-bearing capability of helicoidal lattice samples is gradually improved in the plateau stage,leading to the plateau stress and total energy absorption improved by over 26.9%and 21.2%compared to the uniform sample,*** phenomenon was attributed to the helicoidal design reduces the gap in unit cells and enhances fracture *** acoustic properties,the design of helicoidal reduces the resonance frequency and improves the peak of absorption coefficient,while the FG design mainly influences the peak of absorption *** broad range of frequency from 1000 to 6300 Hz,the maximum value of absorption coefficient is improved by18.6%-30%,and the number of points higher than 0.6 increased by 55.2%-61.7%by combining the FG and helicoidal *** study provides a novel strategy to simultaneously improve energy absorption and sound absorption properties by controlling the internal architecture of lattice structures.