Search results for "Fatigue testing"
showing 10 items of 15 documents
A Model for High-Cycle Fatigue in Polycrystals
2018
A grain-scale formulation for high-cycle fatigue inter-granular degradation in polycrystalline aggregates is presented. The aggregate is represented through Voronoi tessellations and the mechanics of individual bulk grains is modelled using a boundary integral formulation. The inter-granular interfaces degrade under the action of cyclic tractions and they are represented using cohesive laws embodying a local irreversible damage parameter that evolves according to high-cycle continuum damage laws. The consistence between cyclic and static damage, which plays an important role in the redistribution of inter-granular tractions upon cyclic degradation, is assessed at each fatigue solution jump,…
Improving surface integrity of additively manufactured GP1 stainless steel by roller burnishing
2020
Abstract Additive manufacturing can rapidly fabricate the desired components by selectively melting and solidifying feedstock, rather than conventional subtractive machining. However, the difference between the two routes in terms of surface integrity of the final component is relevant. This paper presents a strategy to control the surface characteristics of additively manufactured stainless steel by roller burnishing. In particular, process parameters have been carefully selected to improve the surface integrity of the worked material. The quality of the surface has been analyzed in terms of roughness, hardness, microstructure and residual stresses. The overall product endurance under high…
Numerical modelling of fatigue crack initiation and growth of martensitic steels
2010
This paper presents a numerical simulation of micro-crack initiation that is based on Tanaka-Mura micro-crack nucleation model. Three improvements were added to this model. First, multiple slip bands where micro-cracks may occur are used in each grain. Second improvement deals with micro-crack coalescence by extending existing micro-cracks along grain boundaries and connecting them into a macro-crack. The third improvement handles segmented micro-crack generation, where a micro-crack is not nucleated in one step like in Tanaka-Mura model, but is instead generated in multiple steps. High cycle fatigue testing was also performed and showed reasonably good correlation of proposed model to expe…
Fatigue Crack Growth for Different Ratios of Bending to Torsion in AlCu4Mg1
2008
The paper contains the fatigue crack growth test results obtained under proportional bending with torsion in AlCu4Mg1 aluminium alloy [1]. Specimens with rectangular cross sections and dimensions: length l = 90 mm, height w = 10 mm and thickness g = 8 mm were tested [2]. Each specimen had an external unilateral notch with depth 2 mm and radius ρ = 0.2 mm. The tests were performed under the stress ratio R = −1. The notches in the specimens were cut with a milling cutter and their surfaces were polished after grinding. The tests were realized on a fatigue test stand MZGS-100 where the ratio of torsion moment to bending moment was \( M_T (t)/M_B (t) = tg\alpha = \sqrt 3 /3,1{\text{ }}and\sqrt …
Proposal for a more accurate physically based S–N curve for welded steel joints
2009
Abstract The present article proposes a more accurate S–N curve in the high cycle fatigue regime for fillet welded joints in steel subjected to constant amplitude loading. The S–N curves are constructed based on a physical model of the fatigue damage evolution. It is a two phase model where the crack initiation is treated by a local weld notch approach. The subsequent growth is based on the concept of the stress intensity factor at the crack front by applying the Paris law. According to the proposed model, the time to crack initiation becomes the dominant part of the fatigue life at low stress range levels. The resulting S–N curves are non-linear for a log–log scale and they do not predict …
Fatigue crack initiation and subsequent crack growth in fillet welded steel joints
2019
Abstract The fatigue damage evolution in fillet welded steel joints where cracks are emanating from the weld toe is investigated. Based on existing experimental data for as-welded joints including crack depth measurements of the early crack growth it is proposed to make a distinction between the crack initiation phase and the subsequent crack growth phase. The welded detail in question is an F class detail with plate thickness 25 mm made of medium strength carbon steel. It is found that the crack initiation phase defined at a crack depth of 0.1 mm is close to 25% of the fatigue life even at a relatively high constant stress range of 150 MPa. At lower stress ranges it is concluded that the i…
Crack growth models for multiaxial fatigue in a ship’s propeller shaft
2021
Abstract A premature fatigue failure of a large intermediate propeller shaft in a shuttle tanker is discussed and analyzed. The short fatigue life consists mainly of a crack growth phase. Life predictions are carried out by crack growth modelling based on engineering fracture mechanics. The purpose of the present investigation is to identify the most likely loading modes based on the evolution of the crack propagation. A Linear Elastic Fracture Mechanics Model (LEFM) is applied with the stress intensity factor range entering the Paris law as a key parameter. Existing formulas for the geometry functions are supplemented by more detailed stress intensity factor calculations pertaining to smal…
Accceleration of Fatigue Tests of Polymer Composite Materials by Using High-Frequency Loadings
2004
The possibility of using high-frequency loading in fatigue tests of polymer composite materials is discussed. A review of studies on the use of high-frequency loading of organic-, carbon-, and glass-fiber-reinforced plastics is presented. The results obtained are compared with those found in conventional low-frequency loadings. A rig for fatigue tests of rigid materials at loading frequencies to 500 Hz is described, and results for an LM-L1 unidirectional glass-fiber plastic in loadings with frequencies of 17 and 400 Hz are given. These results confirm that it is possible to accelerate the fatigue testing of polymer composite materials by considerably increasing the loading frequency. The n…
Effect of Cold Working and Ring Indentation on Fatigue Life of Aluminum Alloy Specimens
2013
The article deals with the fatigue life of plates with hole made of aluminum alloy. Specifically, the combined effect of cold working expansion and ring indentation on improved fatigue life performance was investigated. Multiple fatigue tests were performed to determine the cycles to failure and the corresponding W¨ ohler diagram. Experimental results were compared with those of nontreated specimens. The conclusion was that cold working expansion and indentation create a delay on crack formation and fatigue failure.
Critical Planes in Multiaxial Fatigue
2005
The paper includes a review of literature on the multiaxial fatigue failure criteria based on the critical plane concept. The criteria were divided into three groups according to the distinguished fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the applied the critical plane position. The multiaxial fatigue criteria based on two critical planes seem to be the most promising. These two critical planes are determined by different fatigue damage mechanisms (shear and tensile mechanisms).