The stretching rate of the film biaxial stretching apparatus is not a simple operating parameter. It will profoundly affect the microstructural changes and macroscopic mechanical performance of the material during the stretching process, and thus influence the test results. Understanding the relationship between the stretching rate and the test results is crucial for obtaining accurate and reliable data and analyzing the properties of film materials.
When the stretching rate is low, the film material has relatively ample time to respond to the applied external force. In this case, the molecular chains inside the material can slowly adjust and rearrange. The molecular chains have the opportunity to gradually stretch and orient along the force direction, making the molecular arrangement of the film in the stretching direction more orderly. This orderly molecular arrangement will allow the film to show better ductility and flexibility during the stretching process. From the macroscopic test results, at a low stretching rate, the film may require a relatively small force to achieve a large deformation, and its elongation at break will be relatively high, while the tensile strength may be relatively low, because the slow adjustment of the molecular chains allows the material to buffer the impact of external forces to a certain extent.
As the stretching rate gradually increases, the time for the film material to be subjected to external forces is greatly shortened. The molecular chains inside the material do not have time to fully adjust and orient, and the interaction between the molecular chains becomes more complicated. Some molecular chains are pulled by greater external forces before they can stretch, which will cause greater internal stress inside the film. In this case, the film is more likely to experience stress concentration locally. Macroscopically, a higher stretching rate requires the film to withstand greater tensile force to deform during the stretching process, and the tensile strength value obtained by the test will be significantly increased. However, due to the failure of the molecular chains to be fully oriented, the toughness of the film becomes worse, and brittle fracture is more likely to occur, and the elongation at break will decrease accordingly.
Changes in the stretching rate not only affect the mechanical properties test data of the film, but also have different effects on its microstructure. The highly oriented molecular structure formed at a low stretching rate will give the film specific optical and physical properties, such as better transparency and uniformity. However, at a high stretching rate, due to stress concentration and disordered arrangement of molecular chains, defects such as microcracks and voids may appear inside the film. These microscopic defects will be reflected in the macroscopic performance test and affect the overall quality assessment of the material.
Different types of film materials have different sensitivities to stretching rates. Some polymer films have strong molecular chain activity and can achieve good molecular orientation and structural adjustment at a lower stretching rate; while other film materials with greater rigidity or stronger intermolecular forces require a relatively high stretching rate to cause significant changes in the molecular chain. Therefore, choosing the appropriate stretching rate for different materials for testing can accurately reflect their true performance.
In the actual test process, if the stretching rate is not selected properly, the test results may be biased and fail to truly reflect the characteristics of the film material. For example, using too high a stretching rate to test a film with good toughness may break the film prematurely, making the test values of tensile strength and elongation at break lower than the actual level; conversely, using too low a stretching rate to test a brittle film may cause the film to creep during the stretching process, which also affects the accuracy of the test results.
In order to obtain reliable test results, when using the film biaxial stretching apparatus, it is necessary to reasonably select the stretching rate according to the characteristics of the film material, the test purpose and the industry standards. At the same time, it is also very important to maintain the stability of the stretching rate during the test. Any fluctuation in the rate may interfere with the deformation process of the material and cause errors in the test data. If necessary, you can set multiple different stretching rates for comparative testing and comprehensively analyze the test results to gain a more comprehensive understanding of the performance characteristics of the film material.
The stretching rate of the film biaxial stretching apparatus has an all-round impact on the test results from the microscopic molecular chain movement to the macroscopic mechanical performance. Only by fully understanding this influence law and scientifically and rationally selecting and controlling the stretching rate can we ensure that the test results are accurate and reliable, and provide a valuable reference for the research and development, production and quality control of film materials.
