1. When the load on the specimen increases, the compression on the specimen increases. The longitudinal strain increases by increasing of the load value. The young’s modulus gets increases with the longitudinal strain. The load compresses because of the load.
2. When a compressive force acts on the specimen, two types of stain occur one is lateral strain and another strain is the axial strain. The specimen undergoes lateral strain to some extent. The lateral strain occurs due to the overload applied on the specimen, but the specimen undergoes more longitudinal strain than the lateral strain. The specimen has a high level of compression withstanding capacity.
Poisson Ratio = Lateral Strain/Longitudinal Strain; both the compression and the expansion takes place linearly.
3. The lateral strain increases with the longitudinal strain, which was shown in the graph. The specimen undergoes both the lateral and the longitudinal strain simultaneously because of the linear graph. When the specimen undergoes the linear strain, it undergoes compression (Longitudinal Strain) and expansion simultaneously. The fraction of expansion to the fraction of compression is shown in the graph, which is called Poisson ratio
Tensile Stress Demonstration
(A). Stress
The stress is defined as the force per unit area. The stress Is the ratio applied to the force F. The direct stress is known as the stress normal to the plane.
Direct Stress = σ=Fn/A
σ = Normal Stress (Pa) N/M2
Fn = Normal component force (N, lbf (alt, kips))
A = Area (m2, in2)
Shear Stress
The stress parallel to the plane is called shear stress
r = Fp/A
r = Shear Stress (N/M2)
Fp = Parallel Component force (N, Lbf)
A = area (M2, in2)
Strain
Strain is defined as the deformation of solid due to stress
∈ =dllo= σ/∈
dl = Change of length
lo = initial length (Min)
∈ =unit less measure
E = Young’s modulus
Young’s Modulus
Young’s modulus is defined as the ration of stress to the strain
∈ =Stress/Strain = σ/∈
(B) The curve shows the tensile strength (Young’s modulus). After the yield point, the curve slightly decreases because of the dislocation and escaping from the Cotrell atmosphere. After sometime the deformation takes place, the stress increases because of the strain hardening. The deformation continues for a long time and the rupture point is reached. The cross section area decreases because of the Poisson contraction. In the yield stress, at the true elastic limit the dislocation takes place. The stress – strain curve looks like a straight line in proportionality limit, but beyond the elastic limit the deformation occurs. The plastic deformation occurs at the yield strength.
Works Cited
1. The Stress, Strain, Young’s modulus, The Engineering Tool Box. 10 Feb 2011. Web. 11 Feb 2014 http://www.engineeringtoolbox.com/stress-strain-d_950.html
2. Longitudinal Strain and the lateral strain, The strength of materials. Web. 11 Feb 2014 http://strengthofmaterials0111.blogspot.in/2013/06/strain-and-types-of-strains.html
