Abstract This study investigates the initial yield characteristics of closed-cell aluminium foam (Alporas) in multiaxial stress states using experimental and numerical approaches. The mechanical responses of foams with two relative densities (11.7% and 17.2%) are presented in uniaxial compression, uniaxial tension, biaxial compression, biaxial tension and combined tension-compression loading conditions. Cubic and dog-bone specimens are fabricated for uniaxial compression and tension tests respectively. A Modified Maltese Cross Specimen (MMCS) geometry is custom designed for testing closed-cell foams in biaxial stress states. The experimental investigations reveal a consistently stiffer response of closed-cell foams in tensile dominated stress states. This is attributed to the stretching mode of deformation observed in the cell walls in tensile loading conditions, in contrast to the bending/buckling dominant deformation in compressive loading conditions. To complement the experimental data, a wide range of multiaxial stress states is simulated using irregular 3D Voronoi models. An initial yield surface normalized with respect to the uniaxial compressive yield strengths is constructed in the mean-effective stress space using both experimental and numerical data. The normalized initial yield surfaces appear considerably shifted towards the positive mean stress axis. An yield criterion for closed-cell aluminium foams that adequately captures this asymmetric nature of the yield surface about the effective stress axis is proposed, which requires only uniaxial compressive yield strength as a parameter. An empirical relation function estimating the uniaxial compressive yield strength based on the density of the foam material is proposed to facilitate direct application of the yield criterion in early stages of the design.

中文翻译：

---

双轴加载下闭孔泡沫铝的初始屈服行为

摘要 本研究使用实验和数值方法研究了多轴应力状态下闭孔泡沫铝 (Alporas) 的初始屈服特性。两种相对密度（11.7% 和 17.2%）的泡沫在单轴压缩、单轴拉伸、双轴压缩、双轴拉伸和拉伸-压缩联合加载条件下的机械响应。分别为单轴压缩和拉伸试验制作了立方体和狗骨试样。改进的马耳他交叉试样 (MMCS) 几何形状是定制设计的，用于测试双轴应力状态下的闭孔泡沫。实验研究表明，闭孔泡沫在拉伸主导应力状态下的响应始终更硬。这归因于在拉伸加载条件下在单元壁中观察到的变形拉伸模式，与压缩加载条件下的弯曲/屈曲主要变形相反。为了补充实验数据，使用不规则的 3D Voronoi 模型模拟了广泛的多轴应力状态。使用实验数据和数值数据在平均有效应力空间中构建了相对于单轴压缩屈服强度归一化的初始屈服面。归一化的初始屈服面似乎朝着正平均应力轴显着偏移。提出了一种闭孔泡沫铝的屈服准则，该准则充分体现了屈服面围绕有效应力轴的这种不对称性质，它只需要单轴压缩屈服强度作为参数。提出了一种基于泡沫材料密度估计单轴压缩屈服强度的经验关系函数，以促进在设计的早期阶段直接应用屈服准则。