Buckling and Growth of Delamination in Thermoset and Thermoplastic Composites

1991 ◽  
Vol 113 (1) ◽  
pp. 93-98 ◽  
Author(s):  
J. W. Gillespie ◽  
L. A. Carlsson
Keyword(s):  
Composite Laminates ◽  
Strain Energy ◽  
Strain Energy Release ◽  
Thermoplastic Composites ◽  
Beam Model ◽  
Near Surface ◽  
Growth Criterion ◽  
Wide Range ◽  
Instability Growth ◽  
Good Agreement

Compression instability growth of through-width delaminations in composite laminates is investigated. A previously developed beam model that incorporates effects of elastic restraint at the ends of the delamination is combined with a finite element superposition model that yields the Mode I (GI) and Mode II (GII) components of the strain energy release rate. Experimental data were generated for near surface delaminations over a wide range of crack lengths in unidirectional graphite/epoxy and graphite/PEEK laminates. Good agreement between experimentally observed critical loads for crack propagation and analytical predictions was observed using a linear mixed-mode crack growth criterion.

Delamination in Thickness Tapered Composite Laminates

1993 ◽  
Vol 115 (2) ◽  
pp. 193-199 ◽  
Author(s):  
B. R. Trethewey ◽  
J. W. Gillespie ◽  
D. J. Wilkins
Keyword(s):  
Energy Release ◽  
Composite Laminates ◽  
Strain Energy ◽  
Plate Theory ◽  
Strain Energy Release ◽  
Pure Mode ◽  
Element Analysis ◽  
Growth Criterion ◽  
Energy Release Rates ◽  
Failure Loads

The structural performance of thickness-tapered laminates has been investigated using an energy-based damage tolerance methodology. The geometry studied is a thin laminate with discontinuous internal plies and a through-width delamination embedded at the interface between continuous and discontinuous sublaminates. An analytic model, based on shear deformation plate theory and linear-elastic fracture mechanics is employed to determine the Mode I and Mode II components of strain energy release rate. A two-dimensional plane strain finite element analysis is conducted to confirm the accuracy of the analytic predictions. The resulting pure mode strain energy release rates are combined with a mixed-mode growth criterion to predict the axial load required to induce delamination growth. Finally, the analytic and numerical model were used to predict failure in a delamination critical test specimen. Reasonable agreement of the actual and predicted failure loads was observed.

Partial Strain Energy Release Rate for Study Matrix Cracking Evolution in Composite Cross-Ply Laminates

2015 ◽  
Vol 24 (3) ◽  
pp. 096369351502400
Author(s):  
Jean-Luc Rebière
Keyword(s):  
Stress Field ◽  
Composite Laminates ◽  
Strain Energy ◽  
Strain Energy Release Rate ◽  
Strain Energy Release ◽  
Matrix Cracking ◽  
Damage State ◽  
Damage Process ◽  
Cracking Mechanisms ◽  
Observed Damage

Matrix cracking is generally the first observed damage in composite laminates. The stress field distribution in the damaged cross ply laminates is analysed through an approach which uses several hypotheses to simplify the damage state. The proposed cracking criterion involves the respective partial part of the 0° and 90° layers to the damage process. The initiation of transverse and longitudinal cracking mechanisms is predicted.

Strain energy release rates and the fatigue growth of matrix cracks in model arrays in composite laminates

1991 ◽  
Vol 432 (1886) ◽  
pp. 427-444 ◽  
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Composite Laminates ◽  
Strain Energy ◽  
Strain Energy Release Rate ◽  
Strain Energy Release ◽  
Matrix Cracks ◽  
Energy Release Rates

Crack growth in the transverse plies of cross-ply composite laminates has been investigated both experimentally and theoretically. Expressions for the strain energy release rate associated with the growth of cracks in model arrays have been obtained using both the compliance approach and the energy method. Measurements of compliance change with crack length were obtained using glass-epoxy laminates and compared with various predictions. Correlations between the crack growth rate and the strain energy release rate range indicate that a Paris law is applicable.

scholarly journals Measurement of Delamination Fracture Energy Using Stepped Laminates

1992 ◽  
Vol 1 (4) ◽  
pp. 096369359200100 ◽  
Author(s):  
P Gopal ◽  
L R Dharani ◽  
S-C Yen
Keyword(s):  
Energy Release Rate ◽  
Fracture Energy ◽  
Release Rate ◽  
Strain Energy ◽  
Strain Energy Release Rate ◽  
Strain Energy Release ◽  
Mode Ii ◽  
Delamination Fracture ◽  
Mode Of Failure ◽  
Good Agreement

Delamination is often the mode of failure in laminated composites. Therefore the quantification of delamination fracture energy is of vital importance. In this work, externally stepped graphite/epoxy (T300/934) laminates are tested in flexure, resulting in a series of delaminations at 0/90 interface. The delamination fracture energy is calculated based on the strain energy released and is found to be 535 J/m2. This value is in good agreement with the mode II strain energy release rate obtained by other workers.

Chisel Edge and Pilot Hole Effects in Drilling Composite Laminates

2002 ◽  
Vol 124 (2) ◽  
pp. 242-247 ◽  
Author(s):  
M. S. Won ◽  
C. K. H. Dharan
Keyword(s):  
Composite Laminates ◽  
Thrust Force ◽  
Threshold Value ◽  
Entry And Exit ◽  
Drilling Force ◽  
Pilot Hole ◽  
Reinforced Composite ◽  
Wide Range ◽  
Twist Drills ◽  
Good Agreement

Previous studies have shown the severe limitations that have to be placed on machining forces when drilling composite laminates due to their propensity for delamination. Delamination, which consists of separation between the plys in a laminate, is due to the relatively poor strength of these materials in the thickness direction. In drilling, delamination is initiated when the drilling force exceeds a threshold value, particularly at the critical entry and exit locations of the drill bit. While abrasive machining results in damage-free holes in most composites, such processes are slow and expensive when compared to drilling with conventional twist drills. Here it is shown that the chisel edge in such drills is a major contributor to the thrust force that is the primary cause of delamination when drilling composite laminates. In this study, a series of drilling experiments were conducted on carbon fiber-reinforced composite laminates to determine quantitatively the effect of the chisel edge on the thrust force. In addition, tests were conducted to determine the effect of pre-drilling the laminate with a pilot hole. The results show a large reduction in the thrust force when a pilot hole is present which, in effect, removes the chisel edge contribution. An analytical model that incorporates the presence of a pilot hole is also described. The results from the thrust force-feed relationships show good agreement with experimentally determined values for the thrust force for a wide range of feeds for drilling tests conducted on laminates with and without pilot holes.

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