Damage in Composite Laminates

Department of Mechanical Engineering, Sophia University, Tokyo, Japan 

Deformation and Energy Release Rate of Axisynunetric Plates with Multiple Delaminations 

1 Axisynunetric Plate wifl) Multiple Delaminations of ttie Same Size  

A transverse concentrated load, P, is applied at the center of a clamped circular plate of radius R and thickness h with multiple circular delaminations, as shown in Rgure 3. The damaged portion is divided into N pieces of the same thickness by iV-1 equal in size delaminations of radius a. The values relating to the intact and delaminated portions are indicated by subscripts 0 and d, respectively. 

The following assumptions are made in order to simplify the problem. Displacements are small and a linear analysis is valid. The plate is isotropic and the material is uniform. No delamination opens and the frictional force is neglected. Kirchhoff s hypothesis is valid even in the neighborhoods of the delamination edges. The boundary conditions at r = are 

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Shi Y, Soutis C. A finite element analysis of impact damage in composite laminates. RAeS Aeronaut J 2012 116(1186) 1331-46. 

Residual stiffness degradation models have proved capable of estimating the cumulative damage in composite laminates under constant amplitude loading. In a recent publication Lee et al. [51] extended such a model, so that service load spectra could also be predicted. 

Olsson, R. (2001) Analytical prediction of large mass impact damage in composite laminates. Composites Part A Applied Science and Manufacturing, 32, 1207-1215. 

FBG sensors provide a potential solution for strain based SHM techniques especially for composites and bonded structures. In composite materials, FBGs can be embedded inside the composite texture with a negligible effect on the mechanical properties [30, 31, 32, 33]. FBG strain sensors have been used in order to detect microscopic damages in composite laminates [34] and also for the investigation of delamination detection in CFRP laminates [35]. 

Okabe Y, Mizutani T, Yashiro S, TakedaN. Compos Sci Technol. 2002, 62, 951-985. Detection of microscopic damages in composite laminate with embedded small-diameter fiber Bragg grating sensors. 

In the present ehapter, an analytical research on the damage in composite laminates due to a concentrated transverse load is reported. Special emphasis is placed on the interlaminar delaminations below the loading point, which usually occur in the form of multiple delaminations. Figure 1 shows an ultrasonic image of a damage in a quasi-isotropic CFRP laminate created by transverse indentation. Delaminations tended to propagate radially at all interfaces, with accompanying... 

Chapter 16 Impact Damage in Composite Laminates 2.3 Effect of Geometrical Nonlinearity ... 

Figure 6. Three stages of the fatigue damage growth in composite laminates [2]...

O Brien, T.K., Characterization of Delamination Onset and Growth in a Composite Laminate in Damage in Composite Materials, ASTM STP 775, p. 140-167,1982 Poursartip, A. Ashby, M. F., Beaumont P.W.R., The Fatigue Damage Mechanics of Fibrous Laminates in Proceedings of the European Workshop on Nondestructive Evaluation of Polymers and Polymer Matrix Composites, Polymer NDE (edited by Khg. Ashbee), Technomic Publishing, p. 250-260, 1984... 

A statistical analysis based on General Linear Model (GLM) was developed to analyse the influence of loading and off-axis angle on damage of composite laminates. The void content in the composite specimens acted as stress raiser resulting in cracks initiation, propagation and failure as tensile loads progressively applied. Analysis of Variance (ANOVA) was performed for void contents to check the statistical differences caused by the experimental errors. 

Cantwell. W. J.. and Morton, (1985). Detection of impact damage in CFRP laminates. Composite Structures, 3, 3-4, 241-257. 

Susuki 1. Fatigue damage of composite laminate under biaxial loads. In Jono M, Inoue T, editors. Proceedings of mechanical behavior of materials — VI, vol. 2 WS7f3. Kyoto, Japan Pergamon Press 1992. pp. 543—8. July 29-August 2. 

Camanho PP, Matthews FL. A progressive damage model for mechanically fastened joints in composite laminates. J Compos Mater 1999 33 2248-80. 

Forghani A, Vaziri R. Computational modeling of damage development in composite laminates subjected to transverse dynamic loading. J Appl Mech 2009 76. 

Figure 15.5 Effect of impactor size and type on the resulting damage in a laminated GFRP composite. Top row various impactor shapes. Middle and bottom rows back-illuminated images of the impact area for each impactor shape at 4(a—d) and 6(e—h) J impact energy, respectively [8].

Figure 6.10 Low velocity impact damage in a laminated composite on the front surface (left) and the back surface (right)...

Abry, J.K., Choi, Y.K., Chateauminois, A., DaUoz, B., Giraud, G., Salvia, M., 2001. In-situ monitoring of damage in CFRP laminates by means of AC and DC measurements. Composites Science and Technology 61, 855—864. 

Kriz RD, Stinchcomb WW (1982) Effects of moisture, residual thermal curing stresses, and mechanical load on the damage development in quasi-isotropic laminates. In Reifsnider KL (ed) Damage in composite materials, ASTM STP 775. American Society for Testing and Materials, Philadelphia, pp 63-80... 

Stinchcomb, W. W. Nondestructive Evaluation of Damage Accumulation Processes in Composite Laminates, Composites Science and Technology, 25 (1986), p. 103- 118... 

Y. Aoki, H. Suemasu, O. Majima (2001) Damage accumulation in composite laminates during quasi-static transverse loading, Adv. Compos. Mater. 10,219. 

Y. Aoki, H. Suemasu (2001) Fracture mechanical study on mechanism of damage accumulation in composite laminates, Tran. JSME (A) 67,1363 (in Japanese). 

At the microlevel, initial damage in bonded joints is defined by whichever of the two strain invariants reaches its critical value first. At the ends of the overlap in a badly designed bonded joint or test coupon, the dilatational Ji failure mechanism would always occur first. There are no significant peel stresses in the interior of the joint, so the distortional invariant will be exceeded first. The visual consequences of this failure may seem to be one of dilatation because the first indication is the formation of a series of hackles formed at roughly 45° from the adherends being bonded together, as shown in Fig. 44.3. (Exactly the same model applies for in-plane-shear failures in the matrix between parallel fibers in composite laminates.) These are, in reality, failures by distortion, which result in tensile fractures perpendicular to the highest principal stress. 

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