Wen Jie Peng

Ultrasonic Fatigue Tests on a High Strength Steel for Welded Structure

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.

An Investigation of the Fatigue Property of Ultra-High Strength Mould Steel at 130 Hz and 20 kHz

In this paper, the fatigue property of ultra-high strength mould steel is investigated. The fatigue specimen is designed particularly due to the ultra-high strength. Fatigue tests are conduced using ultrasonic and conventional fatigue testing machines respectively. The same geometry and size of the ultrasonic fatigue specimens and conventional fatigue specimens are adopted to overcome the size effects. The test results are compared to investigate the frequency effect.

On the Research and Application of Ultrasonic Fatigue Testing Technology

In the present paper, the characteristic and the application of ultrasonic fatigue testing technology is illuminated. The main problems i.e. the size effect, the thermal effect and frequency effect due to the high frequency are discussed. The results show that: 1. As there is a size effect, a uniform specimen size should be adopted in the very-high cycle fatigue standard and for special designed specimen the designed size should be noted along with the fatigue test results; 2.the heat generation attributes mainly to the low yield strength and the high applied stress, as a result, ultrasonic fatigue testing technology can be mainly applied to the ultra-high cycle fatigue test of high-strength steel; 3.the frequency effect is related to the crystal structure of metallic materials, however, ultrasonic fatigue testing technology can be applied to conduct the comparison of the fatigue properties of the same steel grade before and after the smelting process.

The Fatigue Performance Test on Automotive Frame Steel Using Two Dimensional Up-and-Down Method

The fatigue performances of two types of automotive frame steel include WL510 and WL590 are test with both traditional up-and down method and two dimensional method. In order to take the thickness effect into account, two series of WL510 samples with 6mm and 8mm thickness respectively are selected. Some important parameters of the two dimensional up-and-down method is introduced. Six cases of testing using two dimensional method are compared with the tradition one. Results shows that the fatigue limits of two dimensional method are much closer to the full sample results than the traditional one dimensional method. When the number of the test samples decreases, the deviation becomes larger, and the deviation is still very large even use two dimensional method when the test is with very few samples. In order to guarantee the result accuracy, at least 4 stress pairs are suggested be kept in the test.

An Investigation of Size Effect on Fatigue Property of 3000 MPa-Class Mould Steel Under Ultrasonic Fatigue Testing

Ultrasonic fatigue testing was conducted for 3000 MPa-class mould steel to investigate the fatigue behavior. The fatigue specimen is designed particularly due to the ultra-high strength. Ultrasonic fatigue tests are conduced using two types of specimen sizes and the test results are compared to investigate the size effect on the fatigue property.

The Important Influencing Factors of Coefficient of Friction Testing on Metallic Sheet and Strip

The importance of the coefficient of friction test in sheet metal forming field is introduced. Metallic sheet and strip testing method for coefficient of friction is described, the experimental principle of the testing method is introduced. Three important factors, which will obviously effects the test results, including testing mould, specimen width and surface lubrication conditions have been carefully studied. The comparatively stable testing technologies have been developed to guide the test.

Research Development of Residual Stress Determination with Generalized Stress Increment Testing Method

The idea of generalized stress increment testing method which contains both the stress free method and the stress superimposing method for the residual stress determination is developed. The research development of full and partial stress free testing methods is reviewed. Different testing methods are characterized according to the different working conditions. The stress superimposing testing method of residual stress is different from the stress free one. 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 principal and application of two new type of stress superimposing testing methods of residual stress are introduced, their disadvantages are also indicated.

Research Progress of Stress Superimposing Method for Residual Stress Determination

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.