Fatigue Life Of Notched Specimens Research Articles

Multiaxial Low Cycle Fatigue Life of Notched Specimen for Type 316L Stainless Steel under Non-Proportional Loading

This study discusses multiaxial low cycle fatigue life of notched specimen under proportional and non-proportional loadings at room temperature. Strain controlled multiaxial low cycle fatigue tests were carried out using smooth and circumferentially notched round-bar specimens of type 316L stainless steel. Four kinds of notched specimens were employed with elastic stress concentration factors, Kt, as 1.5, 2.5, 4.2 and 6.0. The strain paths include proportional and non-proportional loadings. The former employed was a push-pull straining and a reversed torsion straining. The latter was achieved by strain path where axial and shear strains has 90° phase difference but their amplitudes are the same based on von Mises' criterion. The notch dependency of multiaxial low cycle fatigue life and the life estimation are discussed with employing inelastic finite element analysis. The lives depend on both Kt and strain path. The strain parameter for the life estimation is discussed with the non-proportional strain parameter proposed by an author with introducing Kt. The proposed parameter gave a satisfactory evaluation of multiaxial low cycle fatigue life for notched specimen of type 316L stainless steel under proportional and non-proportional loadings.

The Effect of Residual Stresses Induced by Prestraining on Fatigue Life of Notched Specimens

The effect of tensile prestraining-induced residual stress on the fatigue life of notched steel parts was investigated. The study was performed on AISI 4140 steel. Rotating bending fatigue tests were carried out on semicircular notched specimens with different notch radii in the as-quenched and tempered conditions. Metallography of the specimens was performed by means of light optical microscopy. The finite-element method was used to evaluate the residual stress distribution near the notch region. Fatigue tests revealed fatigue life improvement for notched specimens, which changes depending on the notch radii and applied stress. Scanning electron microscopy was used to examine the fracture surfaces of the specimens.

Effect of Loading Sequence on the Fatigue Life of Notched Specimens Made From Steel and Aluminium Alloys

A statistical parameter which can be derived from the Markov matrix has been defined in order to characterize the intermixture of random loading fluctuations. By means of this intermixture parameter, load sequences for fatigue tests can be generated closer to reality, and thus more reliable effects as well as effects resulting from loading sequences can be taken into account quantitatively in life calculations. The intermixture parameter has been calculated for 17 test load sequences. The corresponding fatigue test results obtained for notched specimens (Ki = 1.4–3.6) made from steels or aluminium alloys, either under bending or axial loading, led to a general relation between intermixture and fatigue life, being primarily influenced by the stress ratio.

Frequency and Hold-Time Effects on Low Cycle Fatigue Life of Notched Specimens at Elevated Temperature

This paper describes the frequency and hold-time effects on high temperature low cycle fatigue for round notched specimens. Unnotched and notched specimens having different elastic stress concentration factors were fatigued under triangular and trapezoidal stress waves at frequencies ranging from 5 Hz to 0.0001 Hz at 873 K. The three specific fracture characteristics were observed: cycle dependent, time dependent, and cycle-time dependent. The respective notch sensitivity occurred in the respective fracture regime. The fatigue life of notched specimens was predicted from the elastic-plastic-creep cyclic FEM analysis using the linear damage rule and the strain range partitioning rule. Both the life prediction methods predicted the creep-fatigue life within almost a factor of two scatter band.