Deep-Joint Tear Analysis of Shoulder Residual Strain Crack in Pullout Mold
Introduction
Deep-joint tear is a crack in the shoulder area of a moulded part that usually occurs when the material between the moulded part and the mould has been pulled apart due to a high force applied during the pull test. This type of defect is rare but can be debilitating in terms of performance and aesthetics, as the part may have a retaining zone or gap which can degrade the performance and appearance of the product. To analyze the deep-joint tear phenomenon, we will use the finite element method (FEM) to simulate the pull-out test and then conduct microscopic data analysis to ascertain the cause of the deep-joint tear.
Simulation
The Pull-out Test is a typical test used to measure a product’s resistance to pull-out force and can detect any deep-joint tear that might occur before production. The FEM simulation was then used to model a tensile test on the moulded part in order to observe the shape of the deep-joint tear and the corresponding force-displacement diagram. The material model used for the simulation was plastic with a linear elastic model. The modal was validated by measuring the simulated Poisson’s ratio of the model and the experimentally measured Poisson’s ratio of the moulded part.
Measurement
The deep-joint tear in the moulded part was then measured under an optical microscope at a magnification of 200× and compared with the FEM simulation. The results of this comparison showed that the tear was an angle-shaped notch that was 0.2 mm wide and 0.6 mm deep, situated 1.5 mm away from the shoulder area of the moulded part.
Analysis
In order to determine the potential cause of the deep-joint tear, a more detailed analysis was carried out on the shoulder area. This analysis showed that there was a significant residual strain in the shoulder area from the moulding process, which when combined with the high force applied during the pull-out test created a radial crack in the shoulder area of the moulded part. This radial crack was the cause of the deep-joint tear.
Conclusion
The experimental results show that the deep-joint tear in the moulded part was caused by a residual strain in the shoulder area due to the moulding process. This residual strain was then combined with the high force applied during the pull-out test to create the deep-joint tear. These findings provide an insight into the cause of deep-joint tear in pullout moulds and can be used to inform designers of the potential failure points in the product design.
