Lecture 9 – Deformation and Damage Review of terms: Normal stress, σ: Force per unit area applied perpendicular to the plane Normal strain, ε: Change in length per unit of length in the direction of the applied normal stress. Plastic strain: the strain not recovered during unloading Elastic strain: the strain recovered during unloading Degree of plasticity: (plastic strain)/(total strain) Degree of elasticity: (elastic strain)/(total strain) 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 9 – Deformation and Damage Review of terms: Modulus of elasticity, E: E = σ/ ε Tangent Definition: slope; Et = (σx + Δx - σ x - Δx )/ (ε x + Δx - ε x - Δx ) Poisson’s Ratio, μ: ratio of strain perpendicular to the applied force to the strain in the direction of the applied force... εz = σz/E ; εy = - μ εz ; εx = - μ εz Shear stress: F/A parallel to surface of the plane, τ Shear strain: change in angle, δ Shear Modulus, G: G = τ/δ 1/26/07 BAE2022/BAE4400 Physical Properties of Biological Materials