Michał Piotrowski

About Fatigue Tests End Criterion in Elevated Temperatures

In this paper there has been presented a new quantitative criterion of the end of a low-cycle fatigue test conducted in the conditions of fixed amplitude loads. In this criterion there is used an analytical description of the parameters of the hysteresis loop and the number of cycles till the fracture. The conducted experimental verification of this criterion enabled to obtain satisfactory results. In the paper it has been stated that the presented criterion can have a special application in the case of tests of metal materials in an elevated temperature.

Effect of strain level on cyclic properties of S355 steel

Fatigue strength of structural materials is estimated using results of experimental tests performed in the low-cycle fatigue, among others. Computation models used for determination of strength are based on an assumption that there is a stabilization interval in low-cycle testing. Based on a review of literature, a conclusion can be drawn that stabilization of cyclic properties occurs rarely and applies to few metallic materials. Due to variability of loading conditions and the effect of low or high temperature, the occurrence of the phenomena of cyclic weakening or strengthening a material can be hardly anticipated explicitly and its course is affected by various factors related to the testing conditions. This creates important difficulties at the very handling of test results and during identification of models used in the course of fatigue strength computation.

Energy Accumulation in Steel, in the Conditions of Constant-Amplitude

This work presents results of fatigue tests of P91 steel specimens under constant-amplitude and programmed loading in temperature T=600°C. Two strain levels, applied in different order, were used for programmed loading. The loading program level changes were introduced for different levels of damage. The tests provided the basis for analysis of strain energy ΔWpl in the function of the number of load cycles under constant-amplitude and programmed loading. It has been found that that the form of a loading program has an influence on the life and value of energy cumulated in the specimen until crack initiation. Verification of Palmgren Miner hypothesis revealed that its effectiveness depends on the loading program and temperature.

Influence of Adhesive Layer on Mechanical Properties of Multilayer Pipes

In the paper the assessment was made of the influence of adhesive layer on strength properties of multilayer pipes. The conducted tests revealed that during the multilayer pipe’s construction process it is necessary to take into account the adhesive’s immediate strength, fatigue life and the change in their values depending on the temperature and the loading working on the pipe in the exploitation conditions. The adhesive’s influence or the lack thereof on the fatigue life depends on the level of stress σmax. This influence is minimal in the area of the greatest working stress and increases along with the decrease of stress.

Effect of Temperature Changes on the Waveform of Fatigue Damage Accumulation

In this paper there have been presented the results of low-cycle fatigue tests of steel P91 samples in the conditions of isothermal fixed amplitude loads as well as loads with a temperature change. Fixed amplitude isothermal loads were conducted on five levels of full strain and in two temperatures T1=20°C and T2=600°C. In the paper there has been found a significant influence of the sequence of temperature changes on the cyclic properties after the temperature change and on the fatigue life. The conducted experimental verification of the Palmgren-Miner hypothesis proved its influence on the temperature changes during the tests.

INFLUENCE OF TEMPERATURE AND LOADING PROGRAM ON THE FATIGUE LIFE OF STEEL P91

Abstract In this paper there are shown the results of low-cycle fatigue testing of steel P91 samples. During the testing there was conducted a fixed amplitude loading testing as well as programmed loading with various sequence degrees of the program. The testing was done in two temperatures: T=20°C and T=600°C. During the testing a cyclic steel weakening was observed without a clear period of stabilization. Greater changes of the cyclic properties were observed in temperature T=600°C. The influence of temperature on the fatigue life was determined in this paper. This influence is dependent on the degree of strain. It’s a minor one in the range of big strain and increases in the process of decreasing the degree of strain. Furthermore, the impact of the loading program type was determined on the test results and fatigue life calculations

The Impact of the Laser Welding Speed on the Mechanical Properties of Joints in Multilayer Pipes

The paper assessed the impact of the laser welding speed on the strength and fatigue properties of the aluminum layer found in multilayer pipes. The conducted experiment has shown that during the adjustment of the welding speed one has to take into account not only the results of static tests, but also the results of fatigue tests. The impact of the welding speed on fatigue life depends on the level of stress max. This level is slight in the area of the biggest stresses and increases along with the decrease in stresses.