Recovery Methods for Athletes＇ Intensive Training and Competition Fatigue

After athletes＇ intensive training and competition, they would suffer from fatigue. Therefore, the measures to recover their motor and nervous systems from the fatigue are very important. In this research, this author tries to investigate the methods to recover one＇ s joints and relax one＇ s nervous system, and detailed methods would also be provided for reference. Objective conditions, like sports fields and equipment, have become relatively satisfactory. There are high-level coaches and athletes who are carefully and scientifically chosen, so that good athletic performance is well guaranteed. To improve sports teams＇ comprehensive sports skills, we have to adopt and grasp some advanced training methods and skills. But after intensive training and fierce competition, athletes＇ motor and nervous system would suffer from fatigue, therefore, it becomes necessary for them to grasp the methods of recovery. In this research, this author tries to investigate the mechanism and methods to recover athletes＇ joints from the fatigue and relax their nervous system.

Nonlinear dynamic analysis and fatigue damage assessment for a deepwater test string subjected to random loads

The deepwater test string is an important but vulnerable component in offshore petroleum exploration,and its durability significantly affects the success of deepwater test operations.Considering the influence of random waves and the interaction between the test string and the riser,a time-domain nonlinear dynamic model of a deepwater test string is developed.The stress-time history of the test string is obtained to study vibration mechanisms and fatigue development in the test string.Several recommendations for reducing damage are proposed.The results indicate that the amplitude of dynamic response when the string is subjected to random loads gradually decreases along the test string,and that the von Mises stress is higher in the string sections near the top of the test string and the flex joints.In addition,the fatigue damage fluctuates with the water depth,and the maximum damage occurs in string sections adjacent to the lower flex joint and in the splash zone.Several measures are proposed to improve the operational safety of deepwater test strings：applying greater top tension,operating in a favorable marine environment,managing the order of the test string joints,and performing nondestructive testing of components at vulnerable positions.

Influence of Spot Welding on Welding Fatigue Properties of CR340 Steel Joints

Total 72 lapped specimens including six different kinds of CR340 steel structures were prepared to study the influence of the spot welding technology on their fatigue characteristics.Fatigue test and group method were employed and performed on each sample to obtain the fatigue experimental data of each structure under four stress levels.The results show that the spot welding technology had a notable impact on the fatigue performance of both the shear and tensile joints.It can significantly improve the fatigue strength of the structure,the consistency and repeatability of experimental data,as well as the stability and reliability of the structure under dynamic load environment.The shear spot welding structure demonstrates the best fatigue performance which is very important for wide application in engineering of this method.

Microstructure characterization and HCF fracture mode transition for modified 9Cr-1Mo dissimilarly welded joint at different elevated temperatures

The high cycle fatigue（HCF） tests of modified 9 Cr-1 Mo dissimilarly welded joint were carried out at different elevated temperatures and the fracture mechanism was systematically revealed. The fatigue strength at 108 cycles based on S-N curve can be estimated as a half of weld joint＇s yield strength for all conducted temperatures, which can be a reliable criterion in predicting the fatigue life. The results show that the inter-critical heat affected zones（IC-HAZs） of both sides are the weak zones due to their low hardness and inferior fatigue resistance property. HAZ of COST-FB2（BM2） is the weakest zone at room temperature due to the existence of numerously distributed defects and the initiation of cracks, either in the surface or interior zone, impacting a crucial effect on the fatigue life of the joint. While at elevated temperatures, fatigue life was controlled mostly by the intrusion-extrusion mechanism at the specimen surface under high stress level and subsurface non-defect fatigue crack origin（SNDFCO） from the interior material under low stress amplitude. With increasing temperature, more and more fatigue failures began to occur at the HAZ of COST-E（BM1） due to its higher susceptibility of temperature. Besides, it is found that the-ferrite in the BM1 has no harm to the HCF behavior of the joint at the conducted temperatures.