Janusz Sempruch

Determination of the Fatigue Properties of Aluminum Alloy Using Mini Specimen

There are situations where taking normative specimens is impossible due to the dimensions of the objects investigated (e.g. extruded sections) and one of the solutions is to use mini specimens. As for non-standard specimen testing, it is essential to define the effect of size on fatigue strength. The research methodology facilitates the determination of fatigue characteristics (S-N) for EN AW-6063 aluminum alloy. The material is used to manufacture the extruded section in the process of extrusion of the material through the extruding die. The methodology assumes the geometry of the mini specimen and the normative specimen. As for the material strength identification, a static tensile test for the specimens made directly from finished elements and preliminarily strained in cycles was carried out. As a result of the cyclic material reinforcement, an increase in yield strength Re was observed, which, in turn, rejects Re as the upper criterion of the high-cycle fatigue range. The essential fatigue tests were performed based on unilateral cyclic tension (R = 0.1). The effect of size on fatigue strength was defined. Theoretically aluminum alloy non-sensitive to changes in the size of the cross-section showed a different strength in mini and normative specimens.

Experimental Verification of the Analytical Method for Estimated S-N Curve in Limited Fatigue Life

The paper presents method for determined S-N curve used only static properties of material. To verified this algorithm, material C45+C was tested to provide reference fatigue characteristics. Tests was carrying out with rotating bending by equipment own design. Test machine was checked for correct working according standard ISO 1143. Verification of analytical method has been realized by statistical calculation assume null hypothesis that coefficient of slope of straight line and absolute term estimated by proposed algorithm is equal to coefficient of slope and absolute term estimated from experimental data. Calculated value of statistics has shown that there is no reason to reject null hypothesis for proposed method.

Steel X2CrNiMo17-12-2 Testing for Uniaxial, Proportional and Non-Proportional Loads as Delivered and in the Annealed Condition

The article presents the results of fatigue life and fractographic testing of steel X2CrNiMo17-12-2 exposed to proportional and non-proportional fatigue loads. The following load types were applied: tension-compressive strength, torsion, proportional combined/complex loads produced by tension-compressive strength and torsion as well as non-proportional combined load – by tension-compressive strength and torsion by the phase shift angle φ=90°. The paper analyses the effect of the load method on the fatigue life and fractography of fatigue fractures recorded, and especially the effect of non-proportional load.

Verification of the Fatigue Test Method Applied with the Use of Mini Specimen

In special situations the fatigue properties of the construction material can be determined using non-standard specimens, for example smaller than the normative ones (the so-called mini specimens). The research presented was made for the aluminum alloy based on the high-cycle fatigue testing methodology. The verification was made by breaking down the results with own tests which involved the use of standard specimens and stands as well as with the literature reports.

Alternative Method for the Determination of a Full S-N Fatigue Profile

This paper presents two methods for estimating the S-N fatigue curve. The first is the traditional linear regression and staircase method. The other, alternative, method is based on random fatigue life, fatigue limit and probability. The both methods provide similar results but the latter one requires fewer test samples

Experimental Method for Plotting S-N Curve with a Small Number of Specimens

Abstract The study presents two approaches to plotting an S-N curve based on the experimental results. The first approach is commonly used by researchers and presented in detail in many studies and standard documents. The model uses a linear regression whose parameters are estimated by using the least squares method. A staircase method is used for an unlimited fatigue life criterion. The second model combines the S-N curve defined as a straight line and the record of random occurrence of the fatigue limit. A maximum likelihood method is used to estimate the S-N curve parameters. Fatigue data for C45+C steel obtained in the torsional bending test were used to compare the estimated S-N curves. For pseudo-random numbers generated by using the Mersenne Twister algorithm, the estimated S-N curve for 10 experimental results plotted by using the second model, estimates the fatigue life in the scatter band of the factor 3. The result gives good approximation, especially regarding the time required to plot the S-N curve.

Analysis of Size Effect in High-Cycle Fatigue for EN AW-6063

Any changes in specimen size in relation to the reference dimensions involve scaling inaccuracies resulting in the variances in strength testing (monotonic, fatigue) results. It is referred to as a size effect. The size effect is described using a cross-sectional coefficient determined for various specimen sizes and test types. The analysed material is aluminium alloy EN AW-6063 T6 with a cross-sectional area of 28, 7 and 3.5 mm2.

Experimental Verification of Analytical Method for Determining the S-N Curve for Alloy Steel

The paper presents the analytical method of determining the S-N curve based on the static material properties. To verify the procedure algorithm, an experiment has been carried out to define the reference fatigue characteristics of material 42CrMo4. The research was performed with the use of the rotary-bending test stand made according to ones own design. The proper operation of the material testing machine was verified compliant with the ISO 1143 standard and presented in the previous paper [7]. To compare the proposed method, different characteristics according to analytical methods from literature have been determined. To verify this approach, statistical calculation has been performed. Statistical method was derived from paper [3]. The best results were achieved by the proposed method. As analytical method can lead to large error, which was presented in the papers [4,7,8], it was decided to use hybrid method. That method is based on analytical method supported by a simple experiment. Verification of this approach has produced satisfactory results.

Verification of Methods Used for Fatigue Testing of Small Steel Specimens Taken from Existing Structures

This paper presents results of fatigue tests performed on standard specimens and minispecimens taken from two EN 1.4301 acid-resistant steel plates of different thickness. The tests were required for determination of the state of vibrating machines made from the same material. The results confirmed that the proposed testing method can be used for experimental tests.

Accuracy of Analytical-Experimental Method for Determining the Fatigue Characteristics in a Limited Life Region

The study discusses the issue of determining the accuracy of fatigue characteristics in a high-cycle fatigue range using analytical-experimental methods. The analytical-experimental methods are defined as a characteristic curve obtained using an analytical method and additional experiment aimed to increase its accuracy. The higher the amount of data the higher the characteristic curve accuracy. The study aims to address the question “what values should be determined experimentally to obtain an S-N curve in a high-cycle fatigue range with a satisfactory estimation of the fatigue life.