Electronic tensile testing machine testing the tensile strength of packaging film

Introduction

As a flexible material widely used in modern industry, the mechanical properties of packaging film are directly related to the protective effect and transportation safety of products. Tensile strength is one of the key indicators to evaluate the ability of packaging film to resist tensile deformation and breakage. With its high precision, programmable control and automatic data collection and analysis, the electronic tensile testing machine has become the core equipment for determining the tensile strength of packaging film. This article will systematically explain the principles, standard methods, operation points and data analysis of packaging film tensile strength testing based on electronic tensile testing machine, aiming to provide professional reference for related testing work.

Test Principle:

The working principle of the electronic tensile testing machine is to apply an axial tensile load to the specimen through the drive system, and at the same time use the force sensor and deformation measurement device to record the force-displacement data in real time until the specimen breaks. According to Hooke's law and the formula of material mechanics, the tensile strength (σ) can be obtained by the maximum tensile force (F_max) and the original cross-sectional area of the specimen (A₀The formula is as follows:

σ = F_max / A₀

The equipment is mainly composed of a loading frame, a precision servo drive system, a high-precision force value sensor, a clamping system (usually including pneumatic or manual fixtures), an elongation measurement device (such as an extensometer or optical tracking system), and computer control and data processing software. For thin soft materials such as packaging films, the gripper should be equipped with a non-slip liner to avoid slipping or pinching the specimen, and to ensure uniform gripping force.

Sample preparation

Packaging film tensile testing needs to follow relevant national or international standards to ensure comparability and accuracy of results. Common standards include ISO 527-3 (Determination of tensile properties of plastic films and sheets) and GB/T 1040.3 (Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets). These standards clearly stipulate the shape, size, preparation method, test speed and environmental conditions of the specimen.

Specimens are usually cut into dumbbell shapes or strips. Preparation is carried out using a standard cutting knife to ensure that the incision is flat and burr-free, and samples are taken along the membrane longitudinally (MD) and transversely (TD) to assess anisotropy. Before testing, the specimen should be conditioned for at least 4 hours in a standard temperature and humidity environment (e.g., 23±2°C, 50±10% RH).

Testing process

Before the formal test, the equipment needs to be calibrated to ensure that the force value and displacement measurement system is accurate. The key steps and parameters are as follows:

When installing the specimen, it is necessary to ensure that its longitudinal axis and the direction of the tensile force are consistent and the force is uniform. During the test, the software draws the stress-strain curve in real time and automatically records data such as breaking force and elongation. It is recommended to test at least 5 valid data per set of specimens and eliminate outliers.

Data analysis

Once the test is complete, the software usually automatically calculates the following typical performance parameters: tensile strength (fracture or maximum stress), elongation at break, modulus of elasticity (calculated by the slope of the initial linear segment of the curve), etc. For packaging films, tensile strength and elongation at break are often used as the core indicators to evaluate their toughness and bearing capacity.

During the analysis, attention should be paid to the shape of the stress-strain curve. For example, a curve showing obvious yield points may indicate that the material has plastic deformation characteristics; while the smooth rise of the curve to the fracture may reflect brittleness. The result report should clearly indicate the test standard, specimen direction, size, test speed and environmental conditions, and give statistical information such as average value and standard deviation.

Notes:

The accuracy of test results is influenced by various factors. Specimen preparation defects such as edge damage and dimensional deviations can directly lead to stress concentration or cross-sectional area errors. Improper selection of fixtures may cause specimen slippage or premature breakage of the clamping site. Too high a test speed can cause the material to respond more brittle, affecting the measurement of elongation at break. In addition, fluctuations in ambient temperature and humidity can have a significant impact on the mechanical behavior of polymer materials, so laboratory environmental control is crucial. Operators should undergo professional training and regularly calibrate and maintain equipment.

Conclusion

Using an electronic tensile testing machine to test the tensile strength of packaging film is a proven and reliable method. By strictly following standard processes and controlling specimen preparation, equipment parameters, and environmental conditions, accurate and reproducible data on the mechanical properties of materials can be obtained. These data have important guiding value for raw material selection, process optimization, quality control, and product development of packaging films. As sensor technology and data analysis software continue to advance, the efficiency and depth of this test method will be further improved.

References

ISO 527-3:2018, Plastics — Determination of tensile properties — Part 3: Test conditions for films and sheets.

GB/T 1040.3-2006, Determination of tensile properties of plastics - Part 3: Test conditions of films and sheets.

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