| 1. |
- Kumar, Rajesh, et al.
(författare)
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Fatigue damage evolution in woven fabric composites
- 2000
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Ingår i: A collection of technical papers of the 41st AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, AIAA/ASME/AHS Adaptive Structures Forum, AIAA Non-Deterministic Approaches Forum, AIAA Space Inflatables Forum, AIAA Dynamics Specialists Conference. - Reaston, Va. : American Institute of Aeronautics and Astronautics, AIAA. ; , s. 1841-1849
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Konferensbidrag (refereegranskat)abstract
- Fatigue testing of 5-harness satin woven laminates indicates damage in the form of matrix cracking in transverse bundles and internal delamination at the tip of these cracks. These damage entities reduce the overall elastic properties of the laminate. The woven laminate is modeled by approximating it to an equivalent cross-ply laminate. The evolution of cracks during constant amplitude fatigue loading is explained by modeling both the cracks and internal delamination and assuming frictional stresses at the delaminated interface
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| 2. |
- Kumar, Raj Senthil, et al.
(författare)
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Cohesive finite element based modeling of damage in composite materials
- 2002
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Ingår i: Applied mechanics and biomedical technology - 2002. - New York : American Society of Mechanical Engineers. - 791836274 ; , s. 11-19
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Konferensbidrag (refereegranskat)abstract
- Damage in composite laminates affects its overall viscoelastic response. Constitutive equations have been developed for composite laminates considering a fixed damage state. A complete description, however, requires suitable damage evolution laws. This paper is focused on studying damage evolution in viscoelastic laminates using a cohesive finite element approach. A two dimensional, four nodded finite element is developed incorporating a rate-independent traction-displacement cohesive law. This element is used in conjunction with plane strain bulk elements behaving in a linear viscoelastic manner to simulate crack evolution between two existing transverse cracks in symmetric cross-ply laminates. The effects of loading strain-rate, ply constraint and initial crack density are studied. This study shows expected trends in the behavior and indicates the suitability of cohesive zone modeling to study damage evolution in viscoelastic composite materials.
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| 3. |
- Kumar, Rajesh Sai Santosh, et al.
(författare)
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A continuum damage model for linear viscoelastic composite materials
- 2003
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 35:3-6, s. 463-480
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a constitutive model for linear viscoelastic orthotropic solids containing a fixed level of distributed cracks. The model is formulated in a continuum damage mechanics framework using internal variables taken as second rank tensors. Use is made of the correspondence principle for linear viscoelastic solids to define a pseudo strain energy function in the Laplace domain. This function is then expressed as a polynomial in transformed strain and tensorial damage variables using the integrity bases restricted by the initial orthotropic symmetry of the material. The constitutive relationships derived in the Laplace domain are then converted to the time domain by using the inverse Laplace transform. The model is applied to the specific case of cross-ply laminates with transverse matrix cracks. The material coefficient functions appearing in the model are determined by a numerical (finite element) method for one cross-ply laminate configuration at one damage level. Predictions of the viscoelastic response are then made for the same laminate at other damage levels and for other cross-ply laminate configurations at different damage levels. These predictions agree well with independently determined time variations of properties by an analytic method (Kumar and Talreja, 2001, Linear viscoelastic behavior of matrix cracked cross-ply laminates. Mechanics of Materials 33 (3), 139-154) as well as with the numerically calculated values. Extension of the model to incorporate effects of transient temperature, physical aging and moisture is outlined
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| 4. |
- Kumar, Rajesh Sai Santosh, et al.
(författare)
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Linear viscoelastic behavior of matrix cracked cross-ply laminates
- 2001
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Ingår i: Mechanics of materials. - 0167-6636 .- 1872-7743. ; 33:3, s. 139-154
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Tidskriftsartikel (refereegranskat)abstract
- The linear viscoelastic behavior of matrix cracked symmetric cross-ply laminates is studied. A lower bound solution and an approximate 3D solution to the properties are obtained by using the elastic-viscoelastic correspondence principle. The accuracy of Schapery's approximate Laplace inversion technique in the solution procedure is discussed
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| 5. |
- Varna, Janis, et al.
(författare)
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A synergistic damage mechanics approach to viscoelastic response of cracked cross-ply laminates
- 2004
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Ingår i: International journal of damage mechanics. - : SAGE Publications. - 1056-7895 .- 1530-7921. ; 13:4, s. 301-334
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Tidskriftsartikel (refereegranskat)abstract
- A synergistic damage mechanics approach, i.e., a combined continuum damage mechanics (CDM) and micromechanics approach, is developed to characterize the viscoelastic response of cross-ply laminates with transverse cracks. The approach relies upon a second-order tensor-based description of damage wherein the crack opening displacement appears as an explicit function. The time variation of this function is calculated by micromechanics and is inserted into the continuum damage formulation. The relaxation moduli calculated for fixed states of damage (transverse crack density) by this approach agree well with independently calculated values by a CDM approach and finite element model. (Example materials: carbon-epoxy and glass-epoxy composites.)
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