On angled crack initiation under biaxial loading

1984 ◽  
Vol 19 (1) ◽  
pp. 51-59 ◽  
Author(s):  
C W Woo ◽  
L H Ling
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Test Specimen ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Crack Problem ◽  
Complex Loading ◽  
Loading Conditions ◽  
Fracture Criteria ◽  
Crack Growth Behaviour

The angled crack problem has been of growing interest to both designers and researchers for the prediction of the structural integrity of components under complex loading conditions. In the study of angled crack growth behaviour, it is invariably of interest to predict the initial crack growth direction θ0 and the fractures stress σc at which crack initiation occurs. In this paper the merits of the various proposed fracture criteria are reviewed. The biaxial loading effect on the parameter used in each criterion for the prediction of the fracture behaviour is studied. It is observed that the popular testing method employing uniaxial loading of a test specimen is inadequate to demonstrate the suitability of fracture criteria in the prediction of θ0 and σc. It is suggested that with the biaxial loading of a test specimen with an angled crack, a better appraisal of the fracture criteria can be obtained. The experimental results obtained in this study seem to support the maximum stress criteria for both uniaxial and biaxial loading conditions. Both tensions and compression biaxial loading effects have been considered.

Fatigue Crack Growth of Notched Tubular Specimen under Biaxial Loading Conditions

2006 ◽  
Vol 306-308 ◽  
pp. 139-144
Author(s):  
Hyun Woo Lee ◽  
Se-Jong Oh
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Biaxial Loading ◽  
Fatigue Crack Initiation ◽  
Growth Direction ◽  
Crack Growth Behavior ◽  
Loading Conditions ◽  
Tubular Specimen

Crack growth behavior of S45C notched tubular specimen was studied to predict fatigue crack initiation and crack propagation under biaxial loading conditions. Stress-strain field near the hole was analyzed by ANSYS. The crack initiation lives and the crack initiation locations were predicted from strain based theories, and the analysis results were compared with the test results. Crack propagation behaviors were studied to understand the reason of crack branching and crack growth rates changing under biaxial loading conditions. Crack growth direction was also observed to find the governing factors of the fatigue damage under biaxial loading conditions.

Characterization of Fatigue Crack Propagation Under Complex Biaxial Loading

2016 ◽  
Author(s):  
Rajesh Kumar Neerukatti ◽  
Siddhant Datta ◽  
Aditi Chattopadhyay ◽  
Nagaraja Iyyer ◽  
Nam Phan
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Biaxial Loading ◽  
Biaxial Tension ◽  
Fatigue Behavior ◽  
Complex Loading ◽  
Fatigue Tests ◽  
Multiaxial Loading ◽  
Loading Conditions ◽  
Phase Out

Metallic aerospace components are subject to a variety of uniaxial and multiaxial loading conditions and therefore, characterizing and predicting the fatigue crack growth is of paramount importance to the aerospace industry. The fatigue behavior of metallic materials has been researched over the years and well understood under uniaxial loading conditions. However, aerospace structures are often subject to multiaxial loading and there are a very few studies reported on this topic. In this paper, extensive in-plane biaxial tension-tension fatigue tests were performed on an Al7075-T651 cruciform specimen under varying load conditions such as in-phase, out-of-phase and miniTWIST loading. The fatigue life and crack growth rate were evaluated and fractography was performed to understand the microscale crack initiation and growth under these complex loading conditions.

A study on prognostic analysis of attachment lugs under off-axis loading

2019 ◽  
Vol 10 (6) ◽  
pp. 809-824
Author(s):  
Bharath Kenchappa ◽  
Lokamanya Chikmath ◽  
Bhagavatula Dattaguru
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Structural Integrity ◽  
Fatigue Crack Initiation ◽  
Inequality Constraints ◽  
Computational Method ◽  
Engineering Structures ◽  
Content Type ◽  
Lug Joints

Purpose Lug joints with fasteners play a crucial role in connecting many major components of the aircraft. Most of the failures in the past were credited to the damages initiating and progressing from these types of joints. Ensuring the structural integrity of these fastener joints is a major issue in many engineering structures, especially in aerospace components, which would otherwise lead to fatal failure. The purpose of this paper is to adopting the prognostic approach for analysing these lug joints with fasteners subjected to off-axis loading by estimating the crack initiation and crack growth life of these joints. This data will be useful to estimate the remaining life of these joints at any given stage of operations, which is mandatory in structural health monitoring (SHM). Design/methodology/approach Straight and tapered lug joints are modelled using the finite element method in MSC PATRAN and analysed in MSC NASTRAN. These lug joints are analysed with a push fit fastener. The contact/separation regions at the pin–lug interface are carefully monitored throughout the analysis for various loading conditions. Critical locations in these lug joints are identified through stress analysis. Fatigue crack initiation and fatigue crack growth analysed is carried out at these locations for different load ratios. A computational method is proposed to estimate the cycles to reach crack initiation and cycles at which the crack in the lug joint become critical by integrating several known techniques. Findings Analysis carried out in this paper describes the importance of tapered lug joints, particularly when subjected to non-conventional way of loading, i.e. off-axis loading. There is a partial loss of contact between pin and lug upon pin loading, and this does not change further with monotonically increasing pin load. But during load reversals, there is a change in contact/separation regions which is effectively handled by inequality constraints in the boundary conditions. Crack growth in these lug joints pertains to mixed-mode cracking and is computed through the MVCCI technique. Originality/value Most of the earlier works were carried out on in-plane pin loading along the axis of symmetry of the lug. The current work considers the off-axis pin loading by loading the lug joints with transverse and oblique pin load. The significance of taper angle under such loading condition is brought in this paper. The results obtained in this paper through prognostic approach are of direct relevance to the SHM and damage tolerance design approach where the safety of the structural components is of foremost priority.

scholarly journals 3D characterisation of hydrogen environmentally assisted cracking during static loading of AA7449-T7651

2021 ◽  
Author(s):  
Unai De Francisco ◽  
Felix Beckmann ◽  
Julian Moosmann ◽  
Nicolas O. Larrosa ◽  
Matthew J. Peel
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Environmental Exposure ◽  
Exposure Time ◽  
Transgranular Fracture ◽  
Crack Growth Behaviour ◽  
X Ray ◽  
Environmentally Assisted Cracking ◽  
Boundary Triple ◽  
Gauge Section

AbstractIn this investigation, synchrotron X-ray microtomography was used to perform 3D in situ observations of crack initiation and growth during hydrogen environmentally assisted cracking (HEAC) in tensile samples of AA7449-T7651. Two smooth tensile samples with a 1 mm diameter gauge section were held at a fixed displacement ($$\approx 30$$ ≈ 30 % of yield stress) in warm, moist air ($$\approx 76\,^\circ $$ ≈ 76 ∘ C, 73% relative humidity). The samples were then imaged repeatedly using X-ray tomography until they fractured completely. The tomograms showing the nucleation and evolution of intergranular cracks were correlated with electron microscopy fractographs. This enabled the identification of crack initiation sites and the characterisation of the crack growth behaviour relative to the microstructure. The samples were found to fracture within an environmental exposure time of 240 min. Some cracks in both samples nucleated within an exposure time of 80 min (33–40% of the total lifetime). Many cracks were found to nucleate both internally and at the sample surface. However, only superficial cracks contributed to the final fracture surface as they grew faster owing to the direct environmental exposure and the larger crack opening. HEAC occurred prominently via brittle intergranular cracking, and cracks were found to slow down when approaching grain boundary triple junctions. Additionally, crack shielding from nearby cracks and the presence of coarse Al–Cu–Fe particles at the grain boundaries were also found to temporarily reduce the crack growth rates. After prolonged crack growth, the HEAC cracks displayed ductile striations and transgranular fracture, revealing a change in the crack growth mechanism at higher stress intensity factors.

Specimen Geometry Effects on Creep Crack Initiation and Growth in Parent Materials and Weldments

2011 ◽  
Author(s):  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
David W. Dean ◽  
Kamran M. Nikbin
Keyword(s):  
High Temperature ◽  
Crack Initiation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Parent Material ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference ◽  
Constraint Effects

High temperature crack growth in weldments is of great practical concern in high temperature plant components. Cracking typically occurs in the heat affected zone (HAZ) and often propagates into adjacent parent material (PM). Recently, the importance of constraint effects on creep crack growth behaviour has been recognised and creep crack growth testing on a range of specimen geometries has been performed. Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens using sections taken from a non-stress-relieved 316 steel weldment. These specimens include the compact tension, C(T), middle tension, M(T) and circumferentially cracked bar, CCB, geometries. Results are presented from two long-term creep crack growth (CCG) tests performed on M(T) weldment specimens and these are compared with available data on C(T) and CCB weldment specimens together with both long and short term tests on parent material for a range of specimen geometries. The creep crack initiation (CCI) and growth (CCG) behaviour from these tests has been analysed in terms of the C* parameter. As high levels of residual stress exist in non-stress-relieved weldments, the residual stresses remaining in the weldment specimens have therefore been quantified using the neutron diffraction technique. Long-term (low-load) tests are required on PM specimen to observe specimen constraint effects in 316 steel at 550 °C. When interpreted in terms of the C* parameter the CCG behavior of PM and Weldment materials follow the same trendline on low constraint geometries. However, significant difference is observed in the CCG behavior of PM and weldments on the high constraint C(T) geometry. Long term tests on C(T) specimen weldments are required to confirm the results found.

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