The tensile strength of paper is a key mechanical index to measure its ability to resist tensile fracture, and is crucial for product quality control and research and development in many industrial fields such as packaging materials, printing paper, and special paper products. Tensile testing machines, as the core equipment for material mechanical property testing, can accurately quantify this performance by simulating the behavior of paper under tensile. This paper will systematically describe the principle, standard method, key parameters and result analysis of paper tensile strength evaluation based on tensile testing machine.
Test Standards
The basic principle of the tensile testing machine to evaluate the tensile strength of paper is to clamp both ends of the specified size specimen in the upper and lower clamps of the testing machine, and apply an axial tensile load at a constant rate until the specimen breaks. The instrument synchronously records the load and elongation, so as to calculate the tensile strength, elongation at break and other parameters. Tensile strength is usually expressed as the breaking force per unit width, and is calculated as:
σ = F / w
Among them, σ is the tensile strength (kN/m), F is the maximum force value recorded at the fracture of the specimen (N), and w is the initial width of the specimen (m).
Relevant domestic and foreign standards, such as ISO 1924, TAPPI T494 and GB/T 12914, have strict regulations on specimen size, clamping distance, tensile speed, temperature and humidity pretreatment conditions, etc., to ensure the comparability and repeatability of test results.
Testing process
A complete evaluation process includes specimen preparation, conditioning, equipment calibration, test execution, and data analysis. Key test parameters directly impact the accuracy of the results:
| Stretch speed | Selected according to the standard, such as (20±5) mm/min, ensures a constant strain rate. |
| Clamp distance | The standard clamping distance is usually 180 mm or 100 mm, and the gripper is required to prevent specimen slippage or pinching. |
| Specimen size | The width is usually 15 mm or 25 mm, and the length must meet the clamping requirements. |
| Pretreatment environment | Treatment at temperature (23±1)°C and relative humidity (50±2)% for at least 4 hours. |
| Data acquisition frequency | High enough to accurately capture the breaking point. |
Analysis of results
After the test is completed, the tensile testing machine software usually directly outputs tensile strength, elongation at break, tensile energy absorption (TEA), tensile stiffness and other indicators. When analyzing, pay attention to:
1. The tensile strength index needs to distinguish between the longitudinal (machine direction) and the horizontal direction, and the difference between the two can reflect the anisotropy of the paper.
2. Elongation at break reflects the ductility of the paper and is particularly important for wrappers that need to withstand impact or deformation.
3. The shape of the load-elongation curve (stress-strain curve) provides more information such as material toughness, brittleness, etc.
In terms of technical considerations, the design of the fixture, such as the pneumatic flat grip, is crucial to prevent specimen slippage. In addition, the accuracy of the force value sensor, the accuracy of displacement measurement, and the rigidity of the system are the basis for ensuring the reliability of the data. Fluctuations in ambient temperature and humidity can significantly affect the moisture content of paper, which in turn changes its mechanical properties, so laboratory environmental control is necessary.
Conclusion
Using a tensile testing machine to assess the tensile strength of paper is a well-established, standardized method. By following strict testing procedures and understanding the intrinsic relationship between each parameter and the result, repeatable and highly comparable data can be obtained, providing a solid scientific basis for paper quality evaluation, process improvement, and new product development. In practical applications, combined with other tests such as tear degree and breaking resistance, the comprehensive performance of paper can be evaluated more comprehensively.
References
ISO 1924-2: Paper and board — Determination of tensile properties — Part 2: Constant rate of elongation method.
GB/T 12914-2018: Determination of tensile strength of paper and cardboard.
TAPPI T494 om-13: Tensile properties of paper and paperboard.