Mahanian S, Piziali R L
Mechanical Engineering Department, University of Puerto Rico, Mayaguez 00708.
J Biomech. 1988;21(5):347-56. doi: 10.1016/0021-9290(88)90140-6.
An elastic-plastic finite element analysis is performed on the AIA shear specimen to evaluate its effectiveness to yield ultimate shear strength values. The effect of geometry, material properties, and yield criteria are discussed in the light of applications to human femoral cortical bone. Specimen dimensions are noted as follows: W, width, D, hole diameter and H, distance between holes. As the H/D ratio increases the stress distribution tends more toward pure shear at the same time the overshoot in the shear distribution increases. An H/D ratio equal to 1.2-1.5 is optimal. The H/W parameter does not affect the overshoot noticeably but it does slightly affect the purity of shear. The material parameters do affect the performance of the shear specimen. However, the effect of the material parameters are far more pronounced in the anisotropic case than it is in the isotropic case. In the isotropic case, the Young modulus does not affect the overshoot. The increase in Poisson's ratio does slightly decrease the overshoot. For the anisotropic case, the increase in the ratio of shear modulus to Young modulus in the transverse direction (G/E2) results in an increase in the overshoot (in the shear distribution). The increase in the ratio of the Young modulus in the transverse direction to that of the axial direction (E2/E1) also results in an increase in the overshoot. Creating a notch at the top of the hole is shown to have the effect of decreasing the overshoot. Its effect on the purity of the shear is rather slight. It is found that plasticity is initiated at the sides of the two holes where the tensile normal stresses are maximum. The plastic region first expands around the perimeter of the hole then radially outward; and finally, it expands into the significant region. If the W/H parameter is less than 5, a sizable portion of the width of the specimen around the hole can go plastic with the significant region still being in the elastic state. Such a situation can cause tearing of the specimen across the width. A W/H ratio of 6 or more can prevent that danger. It is also found that the onset of plasticity brings about higher overshoot and higher purity of shear. The notched shear specimen performs better in actual tests and is more reliable in producing shear failures. The shear strength results obtained from AIA shear tests tend to confirm those shear strength results obtained from torsion tests.
对AIA剪切试样进行弹塑性有限元分析，以评估其得出极限抗剪强度值的有效性。结合在人体股骨皮质骨上的应用，讨论了几何形状、材料特性和屈服准则的影响。试样尺寸记录如下：W为宽度，D为孔径，H为孔间距。随着H/D比增加，应力分布更趋于纯剪切，同时剪切分布中的过冲增加。H/D比等于1.2 - 1.5是最佳的。H/W参数对过冲影响不明显，但对剪切的纯度有轻微影响。材料参数确实会影响剪切试样的性能。然而，材料参数在各向异性情况下的影响比在各向同性情况下更为显著。在各向同性情况下，杨氏模量不影响过冲。泊松比的增加确实会略微降低过冲。对于各向异性情况，横向剪切模量与杨氏模量之比（G/E2）的增加会导致过冲增加（在剪切分布中）。横向杨氏模量与轴向杨氏模量之比（E2/E1）的增加也会导致过冲增加。在孔顶部开一个缺口被证明有降低过冲的效果。它对剪切纯度的影响相当轻微。发现塑性在两个孔的侧面开始，此处拉向正应力最大。塑性区域首先围绕孔的周边扩展，然后径向向外扩展；最后，它扩展到显著区域。如果W/H参数小于5，孔周围试样宽度的相当一部分会进入塑性状态，而显著区域仍处于弹性状态。这种情况可能导致试样沿宽度撕裂。W/H比为6或更大可以防止这种危险。还发现塑性的开始会带来更高的过冲和更高的剪切纯度。带缺口的剪切试样在实际测试中表现更好，在产生剪切破坏方面更可靠。从AIA剪切试验获得的抗剪强度结果倾向于证实从扭转试验获得的那些抗剪强度结果。
