Test and Research on the hottest plastic packaging

2022-07-25
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Test and Research on plastic packaging containers IV

IV. shear strength test

in packaging containers, some components are subject to shear, and the deformation of components after shear is shear deformation. The stress characteristics are shown in Figure 17

1 Basic principle

shear strength is the load value that a specimen can bear per unit area under the action of shear force

single side shear strength

σ s= × 104 (PA) (9)

double sided shear strength

σ s= × 104 (PA)

in the formula: P - the maximum breaking load of the sample R - the distance between the center of the test piece and the center of the rotating axis of the disc (n)

b - shear width of sample (CM)

l - length of sample shear plane (CM)

2 ﹐ selection of shear mode and specimen shape

the stress modes generally include single-sided tensile shear, single-sided compression shear, double-sided compression shear and pure shear

according to the requirements of practical application, there are many kinds of shear specimen shapes. The common shear methods and specimen shapes are shown in Fig. 18, FIG. 19, FIG. 20 and Fig. 21

the difference of shear strength values is very significant due to different specimen shapes and stress modes. Table 6 shows the shear strength of glass cloth laminate measured under three shear stress modes at room temperature. It can be seen from the table that the measured values of the stress mode of a sample are quite different from each other

3 selection of test speed

the test speed has a certain impact on the shear strength; Free fall test. Due to the different structure of the material itself, the influence degree is also different. Therefore, when selecting the test speed, the main machine of the testing machine must have enough rigidity, and the characteristics of the material must be taken into account. It is observed from practice that the speed is too high, the test results are not stable enough, and the error is relatively large. Generally, it should be less than 25mm/min. Refer to table 7

Author: zhaoyanwei

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