Tensile Strength- Estimation methods, Principles and Factors affecting the values.

-Omkar Kshirsagar-Saket Mulge-Renuka Patil-Sravya Nuguri

Introduction

One of the fundamental methods in material science.

Sample is subjected to controlled tension until failure.

Results are used for the selection of materials for various purposes considering how it will react under different types of forces.

Properties measured – UTS (Ultimate Tensile Strength), Maximum elongation, Reduction in area.

From these properties following properties can be determined: Young’s Modulus, Poisson’s Ratio, Yield strength

Uniaxial tensile testing – Isotropic materials

Biaxial tensile testing – Composite materials

Introduction

What is Tensile Testing 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.

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

Standard Polymer Tensile Testing Methods

D638 - Test Method for Tensile Properties of Plastics.

D5083 - Fiber-reinforced thermosetting laminates.

D882 - Thin Plastic Sheeting.

D1922 - Tearing resistance of various plastic films and thin sheeting by Pendulum method.

D412 - Vulcanized Rubber and Thermoplastic Elastomers.

D3039/D3039M - Polymer Matrix Composite Materials.

Types Of Tensile Testing

Adhesion/Bond Strength

Crimp joint pull-off force

Peel

Tear resistance

Advantages 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

Basic Approach Step 1: Original shape and size

of the specimen with no load.

Step 2: Specimen undergoing uniform elongation.

Step 3: Point of maximum load and ultimate tensile strength.

Step 4: The onset of necking (plastic instability).

Step 5: Specimen fractures.

Step 6: Final length.

ASTM D638 Cut or injection mold your material into “dog bone” shape under 14mm thickness.   Load the specimen into tensile grips. Begin the test by separating the tensile grips at a constant rate of speed.   Speed can range from 0.05 – 20 inches per minute. The target time from start of test to break should be from 30 seconds to 5 minutes. End the test after sample break (rupture)

ASTM D882

Thin Plastic Film less then 1mm in thickness Load your sample into your grips. Enter your specimen geometry (width,

thickness, and gage length) into your controller.

Speed : 20inch/min

ASTM D1922

Sample is a 63mm x 76mm rectangle The energy loss by the pendulum is

used to calculate an average tearing force.

Test results are presented as tearing force in milli-newtons.

Tearing force lies in the range of 0-800 gram force.

Sample thickness is also reported. Only results for samples of the same thickness can be compared.

ASTM 5083

Specimens are placed in the grips of a Universal Test Machine at a specified grip separation and pulled until failure.

For ASTM D5083 the test speed may be determined by the material specification.

The default test speed is 5 mm/min. Depending upon the reinforcement and type, testing in

more than one orientation may be necessary. The standard specimen has a constant rectangular

cross section, 25 mm wide and at least 250 mm long. Thickness can be between 2 mm (0.079 in) and 14 mm.

Factors Influencing Tensile Strength

The effect of additives and impurities Temperature Geometric size and shape Orientation and Morphology Surface Condition Energy and speed of loading The environment- Humidity. Strains in the article due to external loads Gauge Length Jaw Slippage, deformation due to jaw pressure

higher strain at the neck of the specimen contribute to the error.

Stress-strain graphs of two plastics(a) A rigid polymer at a temperature below Tg- High tensile strength but less area under sress strain graph(b) An amorphous polymer greater than Tg –low tensile strength but more area under stress strain curves

Tensile strength increases with

Effect Of Temperature:

Effect of Additives

References:• The Effect of Temperature and other Factors on Plastics and

Elastomers

-By Laurence W. McKeen

• Effect of temperature on tensile properties of injection moulded short glass fibre and glass bead filled ABS hybrids

- S.Hashemi

• Fundamentals of Material Science and Engineering

• ASTM website

• www.testresources.net

• www.ptli.com