Crack Initiation Study on Aircraft Composite Rib with Semi-elliptical Surface Flaw
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TECHNICAL ARTICLE—PEER-REVIEWED
Crack Initiation Study on Aircraft Composite Rib with Semi-elliptical Surface Flaw V. Sivakumar . G. Bharath Kumar . Ambati Gautham
Submitted: 19 March 2015 / in revised form: 29 September 2015 / Published online: 27 October 2015 ASM International 2015
Abstract A parametric study on crack initiation was done by having different sizes of cracks at different locations in a rib section of an aircraft using finite element techniques. A semi-elliptical surface flaw in a typical Boeing-747 rib section having circular cut-out and experiencing an inplane shear loading was considered for the analysis. A laminated composite square plate around a centrally located cut-out was selected in the wing rib for computation purpose. A delamination has been modeled in between the composite layers in the form of a semi-elliptical surface crack using node duplication technique. As there are no theoretical solutions for mixed mode loading problems, the general purpose finite element package ABAQUS was used to obtain the Stress Intensity Factor (SIF) along the crack edge. These stress intensity factor (KC) values were further compared with the fracture toughness of the material to determine the probability of crack initiation. It was observed that the modes of failure change with the dimensions of the crack and also showed a greater tendency towards the crack initiation.
KIIIc c a E1, E2, and E3
G12, G13, and G23
l12, l13, and l23
rz s13 and s23 n q
Keywords Crack initiation Delamination Stress intensity factor Composite Finite element method
W r I k
List of Symbols K KIc
B
KIIc
Stress intensity factor Critical stress intensity factor for mode 1 Critical stress intensity factor for mode 2
J
Critical stress intensity factor for mode 3 Semi-major axis Semi-minor axis Principal Young’s moduli in fiber direction and other two transverse directions, respectively Shear moduli associated with planes 1–2, 1–3, and 2–3, respectively Poisson’s ratio associated with planes 1–2, 1–3, and 2–3, respectively Normal stress component in out of plane direction Shear stress components in respective 1–3 and 2–3 planes Normal vector Local direction of virtual crack extension Elastic strain energy Applied stress Identity matrix Stress intensity factor for auxiliary field Pre-logarithmic energy factor matrix J-integral
Introduction V. Sivakumar (&) G. B. Kumar A. Gautham Department of Aerospace Engineering, Amrita Vishwa Vidyapeetham, Amritanagar P.O, Coimbatore 641 112, India e-mail: [email protected]
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A minor structural flaw, present anywhere in an aircraft may have catastrophic consequences during its lifecycle, endangering a number of lives. Hence, research on how and when
J Fail. Anal. and Preven. (2015) 15:906–914
an aircraft component fails is of great importance. Various methods for determining the crack growth and the damage tolerance of the damaged component in an aircraft help us determine the reliability of the component for future use. Composites are being widely used in ai
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