Rationale
A tensile strength tester is an instrument used to measure the ability of a material to resist fracture under tensile forces. In paper strength evaluation, the instrument applies axial tension at a constant rate by clamping both ends of a standard-sized paper specimen until the specimen breaks. The instrument records the force value and elongation throughout the process, so that the key mechanical parameters are calculated. Its working principle follows the basic relationship of linear elastic regions of Hooke's law, that is, stress and strain are directly proportional, which can be expressed as:
σ = E · ε
Among them, σ represents stress (the force subjected to per unit area, usually expressed in kN/m or N/m), E is the elastic modulus, and ε is the strain (the ratio of elongation to the original length). Through the force-elongation curve, the instrument can automatically derive tensile strength, elongation at break, tensile energy absorption and other indicators.
The tensile resistance of paper is a key indicator of its reliability, directly affecting its processing suitability and end-use. The data provided by the tester mainly includes the following items:
Tensile strength: refers to the maximum tensile force that can be withstood per unit width of paper, usually expressed in kN/m. It reflects the paper's inherent ability to resist tensile damage.
Elongation at break: The percentage of elongation at break compared to the original length of the specimen. This parameter characterizes the flexibility and ductility of the paper.
Tensile energy absorption: The area under the force-elongation curve, which indicates the paper's ability to absorb energy before breaking, is important for assessing the toughness of the paper.
Modulus of elasticity: The ratio of stress to strain within the limit of proportion, reflecting the rigidity of the paper.
Together, these parameters constitute a complete system for evaluating the mechanical strength of paper, which provides a basis for production quality control and application selection.
Test methodology
Paper tensile strength testing adheres to strict international or national standards to ensure comparable and accurate results. Common standards include ISO 1924 series, TAPPI T 494, and GB/T 12914. Tests typically require constant ambient temperature and humidity (e.g., 23°C, 50% RH), specimens cut to standard dimensions (e.g., 15 mm wide, at least 150 mm long), and balanced under standard conditions. During the test, parameters such as chuck spacing and tensile speed should be set according to the standard. Typical test conditions are shown in the table below:
| Standard name | Specimen width |
| ISO 1924-2 | 15 mm |
| TAPPI T 494 | 15 mm (or 25.4 mm) |
| GB/T 12914 | 15 mm |
| Common clip spacing | 100 mm or 180 mm |
| Stretch speed | 20 mm/min or constant strain rate |
The standardized approach ensures consistency in test results across labs and batches of paper, allowing data to be used for process tuning and performance comparison.
The data from the tensile strength tester directly serves many aspects of paper manufacturing and use. During the production process, through online or offline testing, the influence of slurry ratio, grouting degree, wet chemistry and drying process on the strength of the finished product can be monitored, and the process parameters can be adjusted in time. For example, increasing the proportion of long fibers or optimizing beating often improves tensile strength but may reduce the softness of certain grades.
At the application level, tensile strength data is the key basis for the selection of packaging paper (such as corrugated base paper, paper bag paper), printing paper, and special technical paper. Packaging materials require sufficient tensile strength and energy absorption to withstand the stress of transportation; High-speed printing paper needs to have appropriate strength and elongation to ensure operational stability. Through system testing, users can match the mechanical requirements of paper performance and application scenarios.
Modern tensile strength testers are developing in the direction of greater automation, integration and intelligence. Many instruments have integrated features for automated injection, real-time data analysis, and connectivity to laboratory information management systems. At the same time, the research field pays more attention to dynamic tensile behavior, creep performance, and test methods coupled with multiple factors such as humidity and temperature.
Challenges include accurate gripping and measurement of ultra-thin or high elongation specialty papers, as well as how to more accurately predict the behavior of paper under real-world complex stress states using uniaxial stretch data from the lab. This requires continuous improvement of instrument design and the development of more comprehensive evaluation models.
As a basic tool for the evaluation of paper mechanical properties, the tensile strength tester provides quantitative and reliable strength data. The results are fundamental for guiding the optimization of paper production processes, controlling product quality, and ensuring end-application suitability. Following standardized testing methods and comprehensive evaluation in combination with other performance indicators can provide a more comprehensive understanding and improvement of paper product performance.
References
ISO 1924-2, Paper and board — Determination of tensile properties — Part 2: Constant rate of elongation method.
TAPPI T 494, Tensile properties of paper and paperboard.
GB/T 12914, Determination of tensile strength of paper and cardboard.
Britt, K.W., Paper Properties and Their Measurement. The principles and applications of tensile strength testing are discussed in the relevant chapters.