tafila technical university

Faculty engineering

Exp #1

Tensile test.

Name: Salam Fayez Albaradie.

Date of submission: 2/3/2014.

Lecturer name: Dr.Tamer Alshaqarin

1. Introduction

Tensile testing is a way of determining how something will react when it is pulled apart - when a force is

applied to it in tension.

Tensile testing is one of the simplest and most widely used mechanical tests. By measuring the force required to

elongate a specimen to breaking point, material properties can be determined that will allow designers and

quality managers to predict how materials and products will behave in their intended applications.

Many performance parameters can be measured by well executed tensile testing. The resulting data - a curve of

force vs. extension - shows the tensile profile of the test up to the point where the specimen breaks. Along this

tensile profile there are many points of interest, chief among them the elastic limit and force to break or failure

point.

1.1 Benefits of Tensile Testing

Tensile testing provides data on the integrity and safety of materials, components and products, helping

manufacturers ensure that their finished products are fit-for-purpose and manufactured to the highest quality.

The data produced in a tensile test can be used in many ways including:

To determine batch quality

To determine consistency in manufacture

To aid in the design process

To reduce material costs and achieve lean manufacturing goals

To ensure compliance with international and industry standards

1.2 Applications of Tensile Testing

Tensile testing is used to guarantee the quality of components, materials and finished products within wide

range industries. Typical applications of tensile testing are highlighted in the following sections on:

Aerospace Industry

Automotive Industry

Beverage Industry

Construction Industry

Electrical and Electronics Industry

Medical Device Industry

Packaging Industry

2. Theory

2.1 Stress and strain relationship

When a specimen is subjected to an external tensile loading, the metal will undergo elastic

And plastic deformation. Initially, the metal will elastically deform giving a linear relationship of load

And extension. These two parameters are then used for the calculation of the engineering stress and

Engineering strain to give a relationship as illustrated using equations 1 and 2 as follows

2.2 Graphs illustrating the difference between nominal stress and

strain and true stress and strain.

There are two main types of strain - elastic strain and plastic strain. Elastic strain is the stretching of atomic

bonds, and is reversible. Elastic strain can be related to the stress by Hooke's law :

= Eϵ

Where E is the Young's modulus .

Plastic strain, or plastic flow, is irreversible deformation of a material. There is no equation to relate the stress to

plastic strain.

Several points on the graph can be defined:

A - Limit of proportionality - the point beyond which Hooke's Law is no longer obeyed. This is the point at

which slip (or glide ) due to dislocation movement occurs in favorably oriented grains. The graph is linear up to

this point, and begins the transition from elastic to plastic deformation above this.

B - Yield stress - the stress at which yielding occurs across the whole specimen. The stress required for slip in a

particular grain will vary depending on how the grain is oriented, so points A and B will not generally be

coincident in a polycrystalline sample. At this point, the deformation is purely plastic.

C - Proof stress - a third point is sometimes used to describe the yield stress of the material. This is the point at

which the specimen has undergone a certain (arbitrary) value of permanent strain, usually 0.2%. The stress at

this point is then known as the 0.2% proof stress. This is used because the precise positions of A and B are often

difficult to define, and depend to some extent on the accuracy of the testing machine.

D - Ultimate tensile strength (UTS) - the point at which plastic deformation becomes unstable and a narrow

region (a neck) forms in the specimen. The UTS is the peak value of nominal stress during the test. Deformation

will continue in the necked region until fracture occurs.

E - Final instability point - the point at which fracture occurs, ie the failure point

F - Fracture stress - The stress at which fracture occurs - only obtainable from the true stress-strain curve.

3. Calculation And Figures

3.1. Figures

Graph (1): Engineering stress and strain

Graph (2): ult stress and ult strain

Graph (3): log ult stress and log ult strain

3. conclusions

The material that use in this experiment is aluminum contains impurities which have failure at ultimate stress

equal to 450 mpa. From graph (3) which determine the relation between log ultimate stress and log ultimate

strain The linear slope of this line is (n) The strain-hardening in this experiment n equal to 4.16667±.1 and the

log(A) is equal to 0.05; the failure not happen at the middle of material due to impurities.