SIMULATION OF PROGRESSIVE DAMAGE IN BOLTED COMPOSITE JOINTS

Hannes Koerber 1, Pedro P. Camanho 1

1 DEMEGI, Faculdade de Engenharia, Universidade do Porto

Rua Dr. Roberto Frias, 4200-465 Porto, Portugall

KEYWORDS: Failure Criteria, Progressive Damage Modelling, Bolted Composite Joints

ABSTRACT Recently, a continuum based progressive damage model for fiber-reinforced composites became available in the commercial finite element code ABAQUS. The implemented model uses the Hashin damage initiation criteria [1,2] and damage evolution is based on the work of Matzenmiller [3] and Camanho and Davila [4]. The “ABAQUS damage model” provides a simple tool for structural analysts and designers since the Hashin criteria is very popular and widely used in the industry. However, studies have shown that the prediction of damage onset is not always correct, especially in the case of fiber and matrix compression [5,6]. Furthermore, a linear type material degradation law is applied, originally proposed for the cohesive zone model described in reference [4]. This approach may lead to load over-prediction for damage modes with high amounts of dissipated energy, such as the fiber damage mode. The aim of this study is to compare the progressive damage model implemented in ABAQUS with a model recently developed by Maimí et al. [7]. The later is based on the LaRC04 failure criteria and uses a linear-exponential type material degradation law. The LaRC failure criteria showed excellent agreement with test results of the World-Wide Failure Exercise [6] and the model was implemented into an ABAQUS UMAT user subroutine.

Three-dimensional finite element models for the simulation of damage in bolted composite joints were developed. In particular a bearing failure and net-section failure test, were selected. The LaRC04 based UMAT damage model can either be used in a 2D or 3D formulation. Therefore the consideration of a complex 3D stress field, characteristic for bolted joints in quasi-isotropic lay-ups can be investigated in detail. By comparison, the ABAQUS damage model is limited to elements with plane-stress formulation. To enable a comparison using the same finite element mesh, “continuum shell” elements where used in the case of the ABAQUS damage model. These elements resemble a shell formulation for a standard 8-node solid element.

Thermal residual stresses are considered in the analysis and due to the 3D formulation of the UMAT damage model it is possible to carry out a detailed study of the influence of bolt clamping pressure on the bearing and tensile strength of the selected specimens.

The results of the finite element models are assessed by comparing the numerical results of both formulations with experimental data. Figure 1 shows the predicted fiber damage (in compression ) in the 0º layer of the bearing failure model, and Figure 2 shows the predicted bearing stress-bearing strain relation as well as the mean value of the experimentally measured bearing strength.

Fig. 1: Fiber compression damage in 0° layer (ABAQUS damage model)

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bearing strain [-]

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mean averagebearing strength(experiment)

Fig. 2: Bearing stress-bearing strain relation (ABAQUS damage model)

REFERENCES

1. Hashin, Z., Rotem, A., “Fatigue Failure Criterion for Fiber Reinforced Materials”. Journal of Composite Materials, 7, 448-464, 1973

2. Hashin, Z., “Failure Criteria for Unidirectional Fiber Composites”. Failure Criteria for Unidirectional Fiber Composites, 47, 329-334, 1980

3. Matzenmiller, A., Lubliner, J., Taylor, R.L., “A Constitutive Model for Anisotropic Damage in Fiber-Composites”. Mechanics of Materials, 20, 125-152, 1995

4. Camanho, P.P., Davila, C.G., “Mixed-Mode Decohesion Finite Elements for the Simulation of Delamination in Composite Materials”. NASA/TM-2002-211737

5. Lapczyk, I., Hurtado, J.A., “Progressive damage modelling in fiber-reinforced materials”. Composites: Part A (2007), doi:10.1016/j.compositesa.2007.01.017

6. Hinton, M., Kaddour A.S., Soden, P.D. “Failure Criteria in Fibre-Reinforced Polymer Composites: The World-Wide Failure Exercise”. Elsevier Science and Technology Books, 2004

7. Maimí., P., Camanho, P.P., Mayugo, J.A., Dávila, C.G., “A continuum damage model for composite laminates: part I- constitutive model”, Mechanics of Materials, 39, 897-908, 2007

0°, loading direction