摘要
制备了一种正交梯形蜂窝铝材料,代替传统形式吸能盒作为车辆的吸能装置,研究该材料在面内方向低速碰撞下的力学性能及能量吸收特性. 首先,用胶接的手段制备一种正交梯形蜂窝铝结构,用试验方法研究该材料的面内压缩过程,获得材料的应力与吸能特性. 其次,以理论分析方法研究材料的变形与受力情况,获得材料的吸能特性,并与试验结果进行比较. 最后,以仿真手段模拟材料的受载过程,结合优化设计方法,获得材料的最佳吸能参数分别为板厚0.50 mm,上板边长3.0 mm,此时正交梯形蜂窝铝材料质量比吸能可达28.8 kJ/kg,优于传统形式吸能盒结构,这表明正交梯形蜂窝铝代替传统吸能材料的可行性.
随着汽车数量的增多,行驶过程中出现的交通事故也逐步增加. 当汽车行驶速度过快发生碰撞时,汽车车体出现损坏,当以较低行车速度发生碰撞时,汽车的破坏部位一般出现在车
吸能盒的结构通常为方形,为改善吸能盒的吸能量,改变吸能盒的尺寸、形状、材料成为研究热
吸能盒是车身防撞梁的重要组成部分,它能够在碰撞过程中吸收20%左右的能量,尤其在中低速碰撞中可防止车身纵梁发生变形,以降低车辆的维修成
为满足汽车轻量化设计以及吸收更大的撞击载荷,对吸能盒进行材料填充成为研究热点. 张鹏
随着新工艺、新材料的出现,许多新型轻质吸能材料得到应用,以期起到代替传统吸能盒的作
以上新型结构的性能较传统蜂窝结构有较大的提升,但新型结构的制备一般采用3D打印的形式,制备工艺较传统形式复杂. 本文通过胶接方法制备一种正交梯形蜂窝铝新型吸能材料,通过试验方法分析其在中低速度下的力学性能及吸能情况,与传统车用吸能材料(吸能盒)相比,表明其作为汽车低速碰撞吸能材料的可行性;通过塑性能量耗散理论分析,表明试验结果的可靠性;通过仿真模拟获得仿真结果对标试验结果,从而减少试验次数,进一步通过优化方法优化材料结构尺寸,获得正交梯形蜂窝铝最优构型与最佳比吸能.
1 正交梯形蜂窝铝的制备及试验
1.1 正交梯形蜂窝铝的制备

图1 汽车用吸能盒材料和结
Fig.1 Energy-absorbing box materials and structures for automobile
正交梯形蜂窝铝制备过程如

图2 正交梯形蜂窝铝制备过程
Fig.2 Preparation process of orthogonal trapezoidal aluminum honeycomb
正交梯形蜂窝铝单瓦楞结构形状如

图3 单瓦楞结构形状
Fig.3 The shape of single corrugated structure
1.2 压缩试验过程
压缩试验装置是济南时代试金试验机有限公司制造的YAW-3000A微机控制电液伺服压力试验机,最大压力可达3 000 kN,采用下端加载,上端固定的方法. 当压缩达到60%的材料高度时停止,材料的加载方向为X向,试验获得的数据由程序自动记录,并且工程应力和应变数据自动保存在硬盘中.
当正交梯形蜂窝铝压缩变形时,单位体积比吸能为JSEA
(1) |
式中:σ为应力;ε为应变.
2 结果与分析
2.1 试验结果分析
材料的变形过程如

(a) 应变为0
(b) 应变为0.1

(c) 应变为0.4
(d) 应变为0.6
图4 材料的变形过程
Fig.4 Material deformation process
材料的应力-应变-比吸能曲线如

(a) 应力-应变曲线

(b) 应变-比吸能曲线
图5 材料的应力-应变-比吸能曲线
Fig.5 Material stress-strain-specific energy absorption curve
材料缓慢上升阶段为材料的主要吸能阶段,该阶段处于0.05~0.5变形之间,该阶段之所以会出现逐渐上升趋势是因为材料孔洞坍塌折叠后,平板与孔洞壁堆叠在一起,材料厚度增大,出现应力强化,材料的单位体积比吸能可达25.5 MJ/
2.2 材料吸能理论推导
定义首层压溃应力为最先被压溃的瓦楞在压溃全过程中所受到的平均外部应力. 根据能量守恒定律,压溃全过程中外力所做的功等于塑性变形耗散的能量,其中塑性变形耗散的能量主要为转向竖直方向的棱腰产生皱褶所耗散的能量.
理想情况下材料单胞变形过程如

(a) 理想情况

(b) 实际情况
图6 材料单胞变形过程
Fig.6 Deformation process of material unit cell
单胞的吸能可以简化为两部分[
E=E1+E2 | (2) |
(3) |
式中:,,σy为屈服强度,σu为极限应力,n取0.
用于试验的材料每一层发生形变吸能的瓦楞数约为12个,共17层,实际有效吸能区间约为50%,故通过理论分析单块正交梯形蜂窝铝材料的单胞吸能可达到115 J,在有效应变下应变值为0.5,正交梯形蜂窝铝的单位体积比吸能约为28.56 MJ/
2.3 仿真模拟
非线性仿真材料的基材为5052铝合金,忽略胶黏剂的影响,正交梯形蜂窝铝的参数设置从试验数据获得 5052铝合金密度为2.7 g/c
仿真条件下正交梯形蜂窝铝变形过程如

(a) 应变为0
(b) 应变为0.1

(c) 应变为0.4
(d) 应变为0.6
图7 仿真条件下正交梯形蜂窝铝变形过程 (板厚t0=0.40 mm,上板边长a=2.5 mm)
Fig.7 The simulation deformation process of orthogonal trapezoidal honeycomb aluminum (0.40 mm thickness, 2.5 mm length)
正交梯形蜂窝铝试验与仿真应力-应变对比如

图8 正交梯形蜂窝铝试验与仿真应力-应变对比(板厚t0=0.40 mm,上板边长a=2.5 mm)
Fig.8 Comparison of stress and strain between test and simulation of orthogonal trapezoidal honeycomb aluminum (0.40 mm thickness, 2.5 mm length)
2.4 结构尺寸优化
材料的能量吸收与材料的结构相
(4) |
在一定尺寸范围内,材料受载后应尽量吸收更多的能量.为了加工制备的可行性以及作为蜂窝材料的合理性,孔洞尺寸a应为2.0~5.0 mm,板材料的厚度应为0.20~0.50 mm,在合理的尺寸范围内,做到单位体积比吸能最大化.
蜂窝结构的力学性能与t0/a呈一定关
(5) |
序号 | 因子1 a/mm | 因子2 t0/mm | 响应 /(MJ∙ |
---|---|---|---|
1 | 2.0 | 0.20 | 17.602 |
2 | 2.0 | 0.35 | 24.698 |
3 | 2.0 | 0.50 | 15.809 |
4 | 3.5 | 0.20 | 6.299 |
5 | 3.5 | 0.35 | 17.621 |
6 | 3.5 | 0.50 | 23.198 |
7 | 5.0 | 0.20 | 0.414 |
8 | 5.0 | 0.35 | 10.287 |
9 | 5.0 | 0.50 | 17.549 |

图9 比吸能-上边长-板厚响应面曲面图
Fig.9 Specific energy absorption-upper side length-plate thickness response surface diagram
2.5 不同结构形貌吸能盒吸能对比
各截面类型吸能盒比吸能对比如
截面类型 | 质量比吸能/(kJ∙k |
---|---|
圆 | 18.6 |
正方 | 17.9 |
正六边形(钢 | 20.7 |
正六边形(铝 | 7.3 |
方形阶梯结 | 7.13 |
正交梯形蜂窝铝结构 | 28.8 |
3 结 论
本文制备了一种正交梯形蜂窝铝材料,研究其面向低速冲击吸能特性,以期将其用作汽车碰撞吸能材料,代替传统形式的吸能材料.通过试验与仿真手段研究了材料在低速撞击下的力学性能,得出的结论如下:
1)材料受到外载时,并不是最下或最上层出现变形,而是在材料制备缺陷处首先出现变形,之后逐层压缩,材料的应力-应变在吸能区呈现逐渐上升的趋势,仿真结果与试验结果趋势相同.
2)以板厚0.40 mm,上板边长2.5 mm的单胞为例,研究了材料的变形吸能性能,通过塑形折叠理论得出单胞的单位体积比吸能可达0.28 MJ/
3)对材料孔洞尺寸进行优化,以最佳吸能为目的,获取最佳尺寸结构. 通过仿真优化得出材料的单位体积比吸能与上板边长、板厚存在一定关系,但是材料的单位体积比吸能并不是随着板厚与上板边长比的增大而持续增大,这与材料的密实应变点、密度等参数相关,因此更加精确的吸能公式仍需要大量的试验或者仿真手段进一步完善. 通过与传统形式的吸能盒质量比吸能对比,正交梯形蜂窝铝的质量比吸能为28.8 kJ/kg,要高于传统形式吸能盒,表明正交梯形蜂窝铝代替传统吸能材料是可行的.
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