| 摘要: | 金屬孔洞材料由於其輕量化和高能量吸收能力，在國防領域中展現出顯著的應用潛力。這種材料能夠有效吸收和分散衝擊能量，因此被廣泛應用於軍事裝備和防禦系統。由於孔洞材料的微觀結構不易直接觀察，因此使用有限元素分析透過數值模擬來評估孔洞材料在各種負載條件下的行為，不僅可以節省時間和成本，還能提供對材料內部應力分佈和變形過程的深入洞察，從而有助於優化結構設計和改進其能量吸收特性。
本研究主要探討封閉式多孔金屬材料之機械行為，內容包含壓縮實驗及數值模擬兩大部分。在實驗方面，多孔金屬試片藉由施加不同應變速率的壓力負載觀察其機械行為的應變速率敏感性。實驗結果顯示，隨著應變速率的提高，材料的降伏應力、平台應力以及能量吸收能力均有所增加。在數值模擬方面採用有限元軟體ABAQUS/Explicit 建立多孔金屬材料的數值模型，模擬涵蓋兩種不同的幾何模型，一種是無內部孔隙的實心結構，另一種則是具有規則分佈孔隙的結構。模型的材料性質採用塊材的數值，應力應變曲線則是由實驗壓縮孔洞材料所獲取的實際資料。在塑性模型的選用方面，分別採用了等向性硬化（isotropic hardening）和可壓縮泡沫（crushable foam）兩種模型，並加入材料延性損傷準則，使模擬結果更接近實驗數據。此外，本研究亦使用隨機孔洞分佈之不規則模型，分析孔洞分佈、孔洞大小及孔隙率對空孔結構機械行為之影響，結果顯示較低的孔隙率及較小的孔徑對於提高泡沫材料的壓縮機械性能表現有正面的效益。最終比較規則分佈孔洞的結構與隨機分佈孔洞的結構機械行為及變形機制之差異，結果顯示規則分布孔洞的結構展示了均勻的塑性變形，相比之下，隨機分佈孔洞的結構由於孔洞分佈的隨機性，可能導致較薄的細胞壁，從而引發彎曲及塑性塌陷等現象，進而降低泡沫結構的強度和剛性。而在這兩種模型中，薄孔壁是主要發生變形和塌陷的區域。
;The application of metal foams with internal pores has shown significant potential in the defense industry due to their lightweight and high energy absorption capabilities. These materials effectively absorb and dissipate impact energy, thus widely utilized in military equipment and defense systems. Due to the microscopic structure of porous materials being challenging to observe directly, finite element method (FEM) is able to assess the mechanical behavior of the foam materials under various load conditions through numerical simulation. This method not only saves time and cost but also provides in-depth insights into the internal stress distribution and deformation process, thereby helping to optimize structural design and improve its energy absorption characteristics.
This study primarily investigates the mechanical behavior of metallic foams through both compression experiments and numerical simulations. In the experimental section, specimens of a metallic foam were used in compression test by applying various strain rates. The results demonstrated that the yield stress, plateau stress, and energy absorption capacity increased with the strain rate. For numerical simulations, the FEM code ABAQUS/Explicit was used to establish numerical models of a porous metal. Two geometric models were considered, namely one without internal pores and the other with regularly distributed pores. The material properties imported were from bulk material data, while the stress-strain data were taken from the compression test results of the given foam material. Moreover, two plasticity models, namely isotropic hardening and crushable foam models, were employed in the FEM simulation. A ductile damage criterion was also implemented to align the simulation more closely to the experimental data. Additionally, the effects of pore distribution, pore size, and porosity on the mechanical response of porous structure were investigated using a geometric model of randomly distributed pores. The results indicate that a lower porosity and a smaller pore size are beneficial for enhancing the structural performance and integrity of foam materials. Finally, the comparison between structures with regularly distributed pores and those with randomly distributed pores reveals differences in mechanical behavior and deformation mechanisms. The results show that structures with regularly distributed pores exhibit uniform plastic deformation. In contrast, structures with randomly distributed pores, due to the randomness in pore distribution, may result in thinner cell walls, leading to phenomena such as bending and plastic collapse, which significantly reduce the strength and rigidity of the foamed structure. In both models, thin cell walls predominantly undergo deformation and collapse. |
