In this paper, the ultrasonic fatigue machine which works at frequency of 20kHz is utilized to conduct the ultrasonic fatigue tests on a high strength welding structural steel with symmetric cycle stress R=-1 at room temperature. Two typical specimen geometries are tested: smooth specimen and notch specimen. The fatigue tests of smooth specimen are also carried out on the electromagnetic resonance equipment at conventional frequency. A comparison is made between the fatigue test results at the ultrasonic and conventional frequency.
Increasing attention has been paid on fatigue performance evaluation in the recent years. More efficient fatigue testing methods are imperatively needed to accomplish the test requirement. The modified staircase theory is introduced in this paper. Traditional staircase method and modified staircase method are respectively used to evaluate the fatigue performance of pressure vessel steel Q345R. Results show the fatigue limits are 194MPa and 193MPa respectively, which indicates the modified staircase method can enhance the testing efficiency about 50% and keep the test veracity.
The stress superimposing testing method of residual stress is different from the stress releasing way. A new stress field is introduced adding on the initial state. The residual stress is indentified by the strain increment differences of the material detected in the stress superimposing process. The traditional stress superimposing testing method including hardness and indentation method are reviewed. The principle and application of two new type of stress superimposing testing methods of residual stress are introduced, their disadvantages are also indicated.
Poly(phenylene-sulfide)/ Poly(ether-sulfone) polymer composites (coded as PPS/PES) reinforced by Potassium Titanate Whisker(PTW) and Polytetrafluoroethylene (PTFE) were prepared by compression molding. The effect of the filler on the mechanical and tribological properties of the PPS/PES composites was investigated, based on the evaluation of the composites’ properties and examination of the worn surfaces by means of scanning electron microscopy (SEM). Results showed that the incorporation of the PTW contributed to greatly increase the impact strength,tensile strength,and bending strength of the composites, and apparently improve its tribological performance. The composite had a best synthetical performance when the PTW content was about 20wt. %. The wear mechanism of the composites,which could be closely related to the content of PTW, gradually changed from adhesive wear to particle abrasion with the addition of PTW.
Remote micro-sensors and embedded microelectronic devices develops rapidly resent years due to the arisen net of things and increasing civil, medical or military applications. In order to solve the root stress concentration problem in traditional piezoelectric harvester and enhance the power harvesting efficiency, a new type of harvester with dumb-bell shape statically indeterminate bimorph is developed. Numerical results shows that the driving force is borne by both two ends and the root stress is decrease a lot with the statically indeterminate set. The dumb-bell structure not only makes sure the root strength, but also saves the space at middle whose stress is comparatively small. So the new type of energy harvester can enhance its fatigue life at the same time keep its output power at a high level.
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