Study On The Fatigue Fracture Behavior Of The ABS Annular Specimen

In this thesis, the fatigue fracture behavior of a ABS annular part is studied and the content is a part of my supervisor's scientific research task. The ABS material was modified for maintaining the required property of anti-fracture based on the fracture analysis. Strip and annular specimen were adopted for study. We designed and manufactured on ourselves the injection molding mould of the annular specimen and two sets of equipments for fatigue experiment.First of all the fatigue fracture behavior of the original ABS material was studied, on the basis of that the elasticizer SBS and glass fibre were added respectively to modify the ABS material. Then the modified materials were molded into the strip and annular specimen which were later exposed to the self-made equipments for fatigue test. The strip specimen went through the tensile fatigue test, and the annular specimen endured test under change-stress and change-stress load frequency. Microstructure of the fracture surface of the fractured specimen after fatigue test was characterized relatively. Some conclusions were drawn after the experiment results were analyzed and discussed finally.The main conclusions in this paper were presented as follows:1. The rigidity of the ABS/SBS blend decreased, while the toughness and dynamic mechanical property improved. The rigidity of the ABS/GF blend increased, but the toughness and the dynamic mechanical property went to the bad.2. After the specimen structure changed, a remarkable mechanical property was gained for the ABS/SBS blend in which SBS dosage took up 6% , as well as a good ability to anti-deformation and energy dispersion.3. Influencing factors on fatigue propertyUnder low stress, the ABS/SBS blend got a good dynamic mechanical and fatigue property. As the concentration of GF increased, the fatigue property of the ABS/GF blend worsened. While under high stress, as the SBS dosage increased, the ABS/SBS blend obtained a good fatigue property. The fatigue property of the ABS/SBS blend went to the bad as the frequency decreased. The fatigue property of the ABS/GF blend improved as the frequency declined. The structure had a certain effect on the fatigue property of the specimen.The annular specimen of the ABS/SBS blend containing 6% SBS obtained the best fatigue property under high frequency and low stress. The annual specimen of the ABS/GF blend containing 30% GF got the best fatigue property under low frequency and low stress.4. It could be drawn from the analysis of the fracture surface that those getting a good fatigue property obtained a smooth fracture plane, a large fatigue extended area and a brittle fracture state of the fracture surface. Those obtaining a bad fatigue property got a ductile rupture state of the fracture surface and a small fatigue extended area even had no fatigue extended area sometimes.5. Under the same alternating stress, the fatigue endurance of the specimen took on a certain dispersity. The surface integrity(containing surface roughness, residual stress, histology of the superficial coat etc.), histology equality of the material, fluctuation of specimen size, notch effect, environment .etc were the factors causing the dispersity of the fatigue endurance.