Grzegorz Szala

Comparative analysis of fatigue life calculation methods of C45 steel in conditions of variable amplitude loads in the low- and high-cycle fatigue ranges

ABSTRACT In the paper [1] assumptions for fatigue life calculations in the low- and high- cycle fatigue ranges of metal alloys, have been formulated. Three calculation methods: that expressed in stresses, strains and a mixed (stress-strain) one, have been there presented. In this paper results of fatigue life calculations of C45 steel performed in line with the above mentioned methods have been described, and their comparative analysis has been made. The calculations have been carried out for two-level and multi-level load programs of the varying parameters: maximum load within a load program and different values of spectrum filling factor. The comparative analysis of the results of fatigue life calculations in compliance with the above mentioned methods makes it possible to assess differences in the results and depenendence of the differences on values of load program parameters.

Experimental verification of two-parametic models of fatigue characteristics by using the tests of S55J0 steel as an example

Experimental verification of two-parametic models of fatigue characteristics by using the tests of S55J0 steel as an example This paper presents experimental verification of models of two-parametric fatigue characteristics N(σa, σm) on the basis of results of fatigue tests of specimens made of S355J0 steel. On the basis of comparative analysis of results of computations and fatigue life tests of the specimens, performed under constant amplitude sinusoidal loads of different cycle asymmetry ratios, the most versatile models were distinguished. The tests in question were carried out in the high-cycle fatigue range.

Comments on Linear Summation Hypothesis of Fatigue Failures

Abstract This paper presents a comparative analysis of results of fatigue life calculations with the u se of the linear summation hypothesis of fatigue failures (LHSUZ), confronted with experimental test results. Te calculations and fatigue tests were performed for variable amplitude(VA), two-step and ten-step loading conditions, both in the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) range, for the case of C45 steel as an example. Experimental verification of the hypothesis LHSUZ did not revealed any significant influence of load level and form of load spectrum on conformity of results of the calculation by using the LHSUZ, to results of fatigue tests on C45 steel. However, it enabled to assess magnitude of a correction factor which appears in the considered linear hypothesis.

Effect of the Exponent in the Description of Wöhler Fatigue Diagram on the Results of Calculations of Fatigue Life

The paper presents issues concerning the calculation of fatigue life under programmable load. Aim of this study is to analyze the sensitivity of the calculation method based on the variation of the exponent m used in the description of Wöhler fatigue chart. Arbitrary adoption of the recommendations contained in the FITNET procedures in fatigue module (the path 2b for normal stress) for the value of the exponent m = 5 can lead to significant differences in the calculation of fatigue life. This is due to the fact that the value of the exponent m obtained by experimental test of constructional steels and alloy is in within wide limits of variation from 3 to 30 with mean value in excess of 5. Based on the results of the fatigue life calculations for steel C45 and X5CrNi18-10 (1.4301) is noticeable a significant impact of exponent m on the fatigue life. This effect depends on the strain value in the load spectrum and increases with the increase of the maximum amplitude of stresses in the program Sa max.

Description of Cyclic Properties of Steel in Variability Conditions of Mean Values and Amplitudes of Loading Cycles

The work includes description of determination of two-parametric fatigue characteristics (TFC) on the base of experimental test results and description of mathematical models of these characteristics. Mathematical models were verified in C45 and 41Cr4 tests that are essentially different from the point of view of mechanical properties. On the base of analysis of verification test results there were determined ranges of applications of TFC models described in the work.

Influence of Stresses below the Fatigue Limit on Fatigue Life

According to the performed analysis of fatigue phenomena occurring in metals, the effects of fatigue appear in the form of lines and slip bands under loading conditions producing variable stresses with values below the fatigue limit of these metals. It is commonly accepted that variable stresses with constant amplitude of values below 0.4 of the fatigue limit do not cause plastic strain in grains (lines and slip bands), thus they do not affect the fatigue life. This study is an attempt of quantitative assessment of the influence of stresses with values below the fatigue limit on fatigue life by using tests with programed two-step loading (variable-amplitude). Tests were performed with the use of C45 steel specimens.

Analysis of a Simplified Method for Determining Fatigue Charts ΔS-N on the Example of Welded and Soldered Connectors

Abstract The paper describes the method of determining fatigue charts ΔS-N, which is particularly useful in the description of fatigue properties of welded and soldered joints. This method is based on IIW (International Institute of Welding) guidelines and FITNET procedures. This method makes it possible to design ΔS-N charts in a probabilistic approach, which is important in the reliability analysis of structural elements. The work also contains examples of charts resulting from the development of test results for selected welded and soldered joints.

Bulkhead Door – Critical Evacuation States

Abstract The article is a preliminary to a modification concept of the sliding watertight bulkhead door used on ships and vessels. Hydraulic or electro-hydraulic drives used to move these doors require complicated and extended pressure installations with large amounts of hydraulic fluid. Well-known operational drawbacks of these installations include high level of noise and possibility of various leaks in the hydraulic system. Being the first in a series, the present article describes and analyses critical states which can take place during evacuation of people through openings in the watertight bulkhead doors on seagoing ships and vessels.

Application of Two-Parameter Fatigue Charactersitics in Fatigue Persistence Calculations of Structural Components Under Conditions of a Broad Spectrum of Loads

Abstract The paper presents an original method of calculation of the fatigue persistence based on the adoption of the load spectrum in the form of a correlation table, two-parameter fatigue characteristics and the linear hypothesis of fatigue damage summation. The calculation results by the proposed method were compared with the results of fatigue tests programmed for node-seal construction. On the basis of a comparative analysis of the test results and calculations conclusions regarding the usefulness of the proposed method to evaluate the fatigue persistence of components have been reached.

The Issue of Low Cycle Fatigue Scope in the Description of Two-Parameter Fatigue Characteristics

This paper discusses the issue connected with determination of the low cycle fatigue scope for the two-parameter fatigue characteristics. Low cycle fatigue (LCF) and high cycle fatigue (HCF) evaluation criterion for constructional steel (C45, S355J0 and 41Cr4) has been discussed.