Tensile and Elongation Testing for Wrap Films

Discover the critical role of tensile and elongation testing in ensuring stretch wrap films meet industrial durability and performance standards. Learn about ASTM D882, ISO 527-3, and advanced testing methods for tensile strength, elongation at break, and breaking elongation.

Wrap Film Tension and Stretch Test

Why is Tensile and Elongation Testing Essential for Wrap Films?

Wrap films, especially stretch wrap, are subjected to mechanical stress during transport and handling. Testing tensile strength and elongation properties ensures films can stretch without tearing, providing secure packaging.

Wrap films are engineered to stretch under tensile force, allowing them to conform to irregularly shaped loads while maintaining durability. This characteristic reduces material usage without compromising protection.

Standards That Define Tensile and Elongation Testing

ASTM D882-Standard Test Method for Tensile Properties of Thin Plastic Sheeting

ASTM D882 standard focuses on tensile testing of thin plastic films, defining parameters such as strain rate, sample size, and reporting methods to ensure uniformity.

 

Know More About ASTM D882

Plastics — Determination of tensile properties Part 3: Test conditions for films and sheets

ISO 527-3 is An internationally recognized standard for tensile properties, emphasizing plastic films’ behavior under stress and elongation.

Know More About ISO 527-3

Test Overview

Tensile and elongation testing is a fundamental method for evaluating the mechanical properties of packaging films, such as stretch wraps and other materials. It measures how a material reacts to stretching forces, providing essential data like tensile strength, tensile force, elongation at break, and breaking elongation. These parameters are critical for assessing strength, flexibility, and quality assurance in packaging products.

Test Description

A specimen of uniform cross-section is loaded in tension using a mechanical testing machine, such as TST-01 Tensile Tester. During the test, force and/or extension are recorded. A pair of specimen grips are used to hold the specimen, and these grips apply the tensile load, causing the specimen to elongate. The extension is then measured either directly through an extensometer or indirectly via the machine’s motor pulses that control the movement of the grips.

Various combinations of grip separation (distance between grips) and test speed (rate at which the grips are separated) are utilized to simulate different testing conditions. These parameters can influence the material’s behavior during testing.

From the test data, important material properties such as tensile stress (force per unit area) and elongation (increase in length) can be calculated. Tensile stress is typically determined by dividing the force applied by the original cross-sectional area of the specimen, while elongation is calculated based on the change in length relative to the original length of the specimen.

Step-by-Step Test Procedure

1.Select a proper tester force range, gauge length and sample width

About Test Range: To ensure accurate and reliable tensile testing, select a force range such that the specimen fails within the upper two-thirds of the chosen force range. This ensures that the material reaches its ultimate tensile strength and failure point while still operating within the measurable range of the testing machine. TST-01 Tensile Tester provides various ranges of loadcell, such as 30N, 50N, 100N, 200N, 300N, 500N, 700N, 1000N, etc. 

A few trial runs may be necessary to determine the optimal combination of force range and specimen width (or cross-sectional area). The specimen’s width influences the amount of force it can withstand before failure, and adjusting the force range appropriately ensures that the specimen undergoes failure in the expected region of the force curve, providing more useful and precise data.

For wrap film test, normally a 100N or 200N is widely chosen, the specimen width can be 10mm, 15mm, 20mm or 25.4mm. And gauge length, or grip length is set to 50mm or 100mm, according to the width and elongation range in trial tests. 

2.Sample Preparation

Conditioning—Condition the test specimens at 23±2°C (73.4±3.6°F) and 50%±10 % RH for not less than 40 h prior to test unless otherwise specified.

Test Conditions—Conduct the tests at 23±2°C (73.4±3.6°F) and 50±10%RH unless otherwise specified by agreement.

A stip sample prepared by a sample cutter is recommended. For wrap film sampling, a “sandwich” sample is easier for sample taking, in which the sample is placed between two pieces of papers.

film tensile test sample cutter
Tensile Sample Preparation
Tensile Sample Preparation

3.Parameter Setting and Start Test

Place the test specimen in the grips of the TST-01 Tensile Tester, ensuring that the long axis of the specimen is aligned with an imaginary line joining the grip attachment points on the machine. This alignment ensures that the force is applied evenly along the specimen’s length. Tighten the grips evenly and firmly, ensuring a secure hold on the specimen to prevent slipping during the test. The grip force should be sufficient to minimize slippage but not so tight that it causes specimen damage or premature failure at the grip points.

Set the tester crosshead speed at 300mm/min or else. Press the tester TEST button to initiate the protrusion test.

Sample gripping
Sample gripping
Tensile and Elongation Test in Process
Tensile and Elongation Test in Process

4. Calculation of Test Result

Maximum Force: The max force obtained during the test. The maximum force can occur at the yield point, the breaking point, or in the area between the yield point and the breaking point.

Tensile Strength shall be calculated by dividing the maximum force by the original average cross-sectional area of the specimen. The result is expressed in force per unit area, usually megapascals, MPa. 

Percent Elongation at Break shall be calculated by dividing the extension at the moment of rupture of the specimen by the initial gage length of the specimen and
multiplying by 100.

Elongation calculation formula

FAQs about ASTM D5748 Protrusion Puncture Resistance Test

What is the significance of tensile and elongation testing for material characterization?

Tensile and elongation testing is essential for identifying and characterizing materials, providing critical data on their mechanical properties such as strength, flexibility, and durability. These tests help manufacturers and researchers determine whether a material meets control and specification requirements. The data gathered can also guide decisions related to material selection, quality control, and the development of new materials. The results from tensile tests are valuable for understanding a material’s ability to perform under stress, ensuring that it is fit for its intended application.

Why is it important to follow standard procedures when conducting tensile tests?

Tensile test results can be significantly affected by factors such as specimen thickness, testing speed, grip type, and extension measurement method. To ensure accurate and reliable results, it is critical to follow established testing standards, such as ASTM D882 or ISO 527. These standards specify the testing conditions, which must be carefully controlled to ensure consistency and reproducibility. Moreover, specific material specifications may require adjustments to standard procedures, so it is important to refer to these specifications before conducting the test to ensure compliance and meaningful comparisons.

How do tensile properties contribute to material development and quality control?

Tensile properties, such as tensile strength, elongation at break, are vital for research and development as well as quality control in manufacturing. These properties help evaluate the performance of materials in real-world applications. For example, tensile strength indicates how much stress a material can withstand before breaking, while elongation provides insights into its ability to stretch without failure. Consistent testing allows manufacturers to ensure that materials meet the required standards and perform as expected in various environments. By maintaining precise control over test conditions, manufacturers can also optimize their products and ensure that they meet quality assurance criteria.

What factors can affect the results of tensile and elongation tests for wrap films?

Several factors can influence the results of tensile and elongation tests for wrap films, including specimen preparation, test speed, environmental conditions (e.g., humidity and temperature), and film thickness. The alignment of the specimen in the testing machine and the type of grips used are also critical. For accurate results, it’s important to follow standardized methods (such as ASTM D882) and conduct tests under controlled conditions.

How is elongation at break calculated for wrap films?

Elongation at break is calculated by measuring the change in length of the film specimen during the tensile test. The formula is:

Elongation calculation formula
Elongation calculation formula

This measurement indicates the maximum stretch the film can undergo before it breaks, providing insights into its flexibility and ductility, critical for packaging materials that need to stretch without tearing.

How do wrap film tensile and elongation tests contribute to quality control?

Tensile and elongation tests are essential for quality control in the production of wrap films. By ensuring that films meet specific strength and elongation criteria, manufacturers can guarantee product consistency and performance. These tests also help detect defects, such as weak spots or excessive brittleness, that may lead to failure during use. Regular testing allows manufacturers to make adjustments to the film formulation or production process, ensuring that the final product meets the required standards and performs as expected in real-world conditions.

More Tests For Wrap Film