Abstract
Various engineering parts or structures are exposed to fluctuating loads. It is believed that most of these structures or parts fail due to fatigue. Fatigue is considered one of the major problems in engineering because it could lead to catastrophic fractures of components. Therefore, obtaining more information on how the crack behaviour and growth during fatigue could assist in preventing the parts from fracturing.
The current research project joined rods using the rotary friction welding process. These rods were welded with a rotational speed of 1500 rpm, 1800 rpm, and 2100 rpm. The rotational speed was varied to study its effect on the quality of the weld and fatigue life, while other process parameters such as friction pressure, forging pressure, friction time, and forging time were kept constant.
A chemical composition analysis of the base metal 316 L stainless steel was carried out to prove that the correct material was used. Energy dispersive X-ray spectrometer (EDS) analysis was done on the etched parent material and weld zone regions of the three friction-welded samples. A tensile test and fatigue test were conducted on the samples. A 3D scanning of the welded samples was carried out to check the alignment of the two centres of the welded samples.
A tensile test of the parent material was carried out to find the value of the yield strength and ultimate tensile strength of the parent material. The yield strength value was used to estimate the percentage of the stress that the specimens were subjected to. The specimens were subjected to four different stresses (286.981MPa, 229.585 MPa, 172.189 MPa, 133.925 MPa) on a fatigue-rotating bending machine, and the number of cycles each specimen had to reach two million cycles. For the specimens that did not break after reaching two million cycles, the test was stopped. A stress-life (S-N) curve was generated from the results obtained. The fracture surface of the specimens was studied using an optical microscope and scanning electron microscope (SEM).
Based on the results obtained from fatigue testing, it was found that all the specimens welded with a speed of 1500 rpm fractured at all four stresses that were applied during testing. However, specimens welded with a speed of 1800 and 2100 rpm managed to
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reach two million cycles when the stress of 229.585 MPa, 172.189 Mpa, and 133.925 Mpa were applied. Misalignment of the center of the specimens during friction welding was found to be one of the factors that caused some of the specimens to fail or to fracture earlier than expected. The fractured surfaces observed through the use of a microscope of the specimens welded with a speed of 1500 rpm revealed that there was no proper bonding between the two welded specimens.