Cee 300

ABSTRACT

Steel 4340 annealed is a high tensile strength material. The specimen was ran through an Instron load frame until it fractured, in order to calculate the stress strain relationship. The lab results for the ultimate strength were similar to the expected values, but the Young’s modulus was 19 percent different. To have a more accurate estimate of the actual results additional testing of the same material should be ran, so there is more data to compare with expected values.

1. INTRODUCTION

1.1 Tension Test

In the tensile test, a material is subjected to a load, or Force, that measures the resistance along one axis. The force gradually increases causing the subject to deform, and ultimately fracture or break. Tensile testing is used to identify the mechanical and material properties of the specimen, including the stress and strain data.

Two factors are used in order to normalize the testing data received from tension testing. The first is stress. Stress is given by the following equation:

| σ= FAo | (1) |

where σ represents the stress, F represents the tensile load applied along the axis, and Ao is the cross-sectional area over which the load is applied. The cross sectional area is that of the original, prior to any deformation caused by the specimen fracturing. All of the stress compiled in this laboratory is calculated by using Equation (1).

The second factor that is used is the strain. The strain can be calculated using the following equation:

| ℇ= li-lolo= ∆llo | (2) |

where ε represents the strain, Δl represents the change in length of the specimen, li is the instantaneous length and lo is the original length of the specimen prior to the load. Strain is given in a unit-less value.

1.2 Stress Strain Behavior

In order to define the properties of the material, a method based on the stress-strain relationship is used. When represented graphically, this relationship provides a visual representation of the elastic and plastic...