Masayoshi Hasegawa

Effect of strong shot peening cleaning and hot galvanizing on fatigue strength of steel welded joint

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning. The following experimental results were obtained: 1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa. 2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa. 3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory. 4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about − 96 MPa, − 32%) by increase of surface roughness. 5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

Effects of friction welding conditions on initial joining phenomena

Summary This paper describes an investigation into the effects of friction welding conditions on the initial joining phenomena and joining mechanism in the first and second phases of friction welding on a continuous drive type friction welding machine using mild steel specimens. The results obtained may be summarised as follows: At a friction pressure as low as around 35 MPa, the initial joining location shifts from the axial centre of the specimen towards its outside with an increasing friction pressure. If the friction pressure exceeds this value, however, it remains virtually constant. The effect of the friction pressure on the time taken for initial joining to start is pronounced when the friction pressure is less than around 10 MPa. The time taken for joining to start then increases with a decreasing friction pressure. If the friction pressure exceeds this value, however, the time is little changed. The initial joining location virtually coincides with the location where maximum traces are found on t...

Improvement of the fatigue strength of aluminium alloy welded joints by high hardness and large specific gravity shot peening

Abstract The shot peening method, which requires simple equipment and treatment, is extensively employed as a method to improve fatigue strength. However, conventional steel ball shot material has a low specific gravity, so high speed projection is required in order to improve fatigue strength; thus, the accompanying noise and high air flow are problems. Accordingly, in order to improve these aspects, high hardness and high specific gravity shot material has been developed with 1.7 times the hardness (HV1400) and approximately 1.9 times the specific gravity (approximately 14) compared with a conventional steel ball.1,2

Effects of friction welding conditions and weld flash on fatigue strength of steel friction‐welded joints

Summary As‐welded hot‐ and cold‐drawn mild steel solid round bar specimens are used to determine the effect of flash on the fatigue strength of friction‐welded joints in rotating bending fatigue tests. The results obtained may be summarised as follows. The fatigue strength of the hot‐ and cold‐drawn friction‐welded joints with flash decreases with an increasing upset pressure. The fracture location of friction‐welded joints with flash is the flash toe. The upset pressure has a pronounced effect on the fatigue strength, whereas the friction pressure and burn‐off have little effect. The toe radius of the flash decreases with an increasing upset pressure, whereas the toe angle conversely increases. Stress concentration in the flash toe is therefore considered to be the main cause of the greater loss of fatigue strength in friction‐welded joints with flash than in the base metal. The fatigue strength of the hot‐drawn joints recovers to the base metal level under any welding conditions so long as the flash is ...

Fatigue strength of friction-welded joints with flash in various carbon steels

Summary The fatigue strength of friction-welded joints with flash sharply decreases with increasing upset pressure. This is previously reported as being due to the stress concentration caused by the flash. This study examines the effect of flash on preventing any decrease in the fatigue strength of friction-welded joints in rotating bending fatigue tests of S15C, S35C, S45C and S55C machine structure carbon steel friction-welded joint specimens under various friction welding conditions. The results obtained may be summarised as follows: The reduction ratio of the fatigue strength of all carbon steels tested decreases with a decreasing upset pressure. The reduction ratio is smaller in the higher-carbon steel at the same pressure. The friction-welded joints produced from S45C and S55C carbon steels show little loss of fatigue strength at an upset pressure of 64 MPa. Hardening of the flash toe becomes more pronounced in the higher-carbon steel under thermal cycling during friction welding. The stress concent...

Development of joining method of polyethylene branch pipe for gas and non-excavation construction method

The purpose of this study is joining main and branch gas pipes by friction welding without digging a paved road. By this development, only making a hole at the vertical side of the paved road, the branch pipe can be connected to the main pipe. In this study, an end face of branch pipe was welded to a side of the main pipe. Furthermore, considering that the gas main pipe is laid in the ground, the influence of mud on the joining state is examined. The experimental results are as follows. Branch pipe welding without digging a paved road was enabled by the friction welding method. The developed method does not require digging and repairing the paved road. Therefore, construction cost can be reduced, and traffic is not obstructed. Tensile strength and elongation of branch pipe friction welded joint were 17.7–17.8 MPa and 520–525%, respectively. These were nearly equal to those of base polyethylene. A large amount of mud was eliminated from the faying surface by friction. Therefore, the influence of mud on tensile strength and elongation was not recognized.

Study of friction welding of polyethylene pipes

Summary This paper describes an investigation of the effects of the friction welding conditions on the joining phenomena and tensile strength of welded joints produced from polyethylene gas supply pipes in tests conducted on a metal brake-type friction welding machine. The results obtained may be summarised as follows: The friction pressure strongly affects the initial torque and total loss (burn-off) in such a way that the initial torque and total loss sharply increase with an increasing friction pressure. The initial torque and upset pressure found during friction welding of polyethylene pipes are much lower than those found during friction welding of metals. The friction pressure strongly affects the flash size on the outside and inside of the pipes in such a way that the flash size (height of flash and width of flash) sharply increase with an increasing friction pressure. The friction pressure and rotational speed strongly affect the appearance of the friction-welded joints. The tensile strength and e...

Effects of the toe shape of the flash on stress concentration factor in friction welded joints

Summary The authors have previously reported that the fatigue strength of friction welded joints with a flash is markedly affected by the toe shape of the flash caused by friction welding conditions. Accordingly, in this report, the effects of the toe shape of the flash upon the stress concentration factor α of friction welded joints were examined by means of the rotating bending fatigue test. Simulated friction welded joint specimens were employed in the experiments; the stress concentration factor was measured using the copper electro-plating stress measuring technique. The toe shape of the flash was characterised by four factors which were the toe radius r, the toe angle θ, the root height h and the toe width b. The results obtained are as follows: The effects of r upon α were marked when r was small; however, for comparatively greater values of r, the effects were hardly detectable. The effects of θ upon α increased with increasing θ; however, this tendency was hardly noticeable for greater values of ...