X. S. Sun

A multi-axial fatigue model for fiber-reinforced composite laminates based on Puck’s criterion

A new multi-axial fatigue model for fiber-reinforced composite laminates based on Puck’s criterion is proposed in this article. In the fatigue model, fatigue master curves from the ATM are used to determine the uniaxial ply fatigue strengths and the multi-axial fatigue failure is then determined by Puck’s criterion with the fatigue strengths at the ply level. The fatigue master curves from ATM are generated with limited uniaxial fatigue tests and can be applied to fatigue loading conditions with various frequencies and stress ratios. Both uniaxial and multi-axial S-N curves can be derived from thefatigue model. Fatigue failure envelopes are also generated from the model to better interpret the multi-axial fatigue failure in multi-axial stress spaces. The proposed multi-axial fatigue model is based on ply-level predictions, but it can beextended to laminate-level predictions with the CLT or numerical methods such as the FEM. Multi-axial fatigue failures caused by either local or global multi-axiality can be predicted by the model. Both uniaxial and biaxial fatigue experimentswere carried out to provide test data for establishing and validating the proposed fatigue model. The application oftheproposed multi-axial fatigue model is demonstrated with predictions of S-N curves and fatigue failure envelopes of unidirectional laminates and multi-directional laminates with typical lay-up configurations. The predictions from the proposed fatigue model are also compared with various experimental results and reasonably good agreement is observed.

Recent efforts toward modeling interactions of matrix cracks and delaminations: an integrated XFEM-CE approach

This paper presents a novel integrated approach using the extended finite element method (XFEM) and cohesive elements (CEs) for modeling three-dimensional (3D) delaminations, matrix cracks, and their interactions in progressive failure of composite laminates. In the proposed XFEM-CE approach, the matrix cracks are explicitly modeled by the XFEM through nodal enrichment and element partition, and the inter-ply delaminations are modeled by cohesive elements through traction–separation law. An XFEM-based cohesive element enrichment scheme is developed in order to properly model the interactions between the delaminations and matrix cracks. It is critical to enrich the cohesive elements at the local juncture where cracks meet, in order to obtain the correct crack path interactions. Examples are presented for failure analysis of double-cantilever-beam and end-notch-flexure laminates with different layups. The results show strong explicit matrix crack–delamination interactions in these laminates. This work presents another significant development of a computational platform for realistic modeling of progressive damage in composites.

An edge-based smoothed XFEM for fracture in composite materials

In this work, an edge-based smoothed extended finite element method (ES-XFEM) is extended to fracture analysis in composite materials. This method, in which the edge-based smoothing technique is married with enrichment in XFEM, shows advantages of both the extended finite element method (XFEM) and the edge-based smoothed finite element method (ES-FEM). The crack tip enrichment functions are specially derived to represent the characteristic of the displacement field around the crack tip in composite materials. Due to the strain smoothing, the necessity of integrating the singular derivatives of the crack tip enrichment functions is eliminated by transforming area integration into path integration, which is an obvious advantage compared with XFEM. Two examples are presented to testify the accuracy and convergence rate of the ES-XFEM.

Progressive Failure Analysis of Scaled Double-Notched Carbon/Epoxy Composite Laminates

This article presents progressive failure analysis of double-notched carbon/epoxy composite laminates with different scales. A numerical analysis strategy based on material property degradation method (MPDM) and cohesive elements (CE) is developed to model progressive failure of scaled double-notched composite laminates, where the material property degradation method is used to model the intralaminar failure and the cohesive elements are employed to account for the delamination at the interfaces. Different failure theories are considered in the material property degradation method–cohesive element approach and a comparative study of these failure theories is presented. The mesh dependency of the material property degradation method–cohesive element approach is investigated with different notch and element types for the double-notched composite laminates. Size scaling effects are also studied by traditional fracture models and the material property degradation method–cohesive element approach, significantly revealing a trend in strength reduction of notched composites with increasing specimen size. The predictions are compared with the experimental results and reasonably good agreement is observed.

A Modeling Approach Across Length Scales for Progressive Failure Analysis of Woven Composites

This paper presents a multiscale modeling approach for the progressive failure analysis of carbon-fiber-reinforced woven composite materials. Hierarchical models of woven composites at three different length scales (micro, meso, and macro) were developed according to their unique geometrical and material characteristics. A novel strategy of two-way information transfer is developed for the multiscale analysis of woven composites. In this strategy, the macroscopic effective material properties are obtained from property homogenizations at micro and meso scales and the stresses at three length scales are computed with stress amplification method from macroscale to microscale. By means of the two-way information transfer, the micro, meso and macro structural characterizations of composites are carried out so that the micromechanisms of damage and their interactions are successfully investigated in a single macro model. In addition, both the nucleation and growth of damages are tracked during the progressive failure analysis. A continuum damage mechanics (CDM) method is used for post-failure modeling. The material stiffness, tensile strength and damage patterns of an open-hole woven composite laminate are predicted with the proposed multiscale method. The predictions are in good agreement with the experimental results.

EXPERIMENTAL AND COMPUTATIONAL STUDIES ON PROGRESSIVE FAILURE ANALYSIS OF NOTCHED CROSS-PLY CFRP COMPOSITE

This work presents experimental and computational studies on progressive failure analysis of notched cross-ply carbon fiber reinforced polymer (CFRP) composite. The carbon/epoxy composite laminated with [90/0]s layup is tested using double-notched specimens loaded in tension. The load-displacement curve, failure load and damage patterns of all tested specimens are discussed. In addition, a numerical analysis approach based on material property degradation method (MPDM) and cohesive elements (CE) is illustrated to capture complex failure mechanisms and damage progression as observed in the tested specimens. The MPDM is used to model the in-plane failure of 90° plies and 0° plies while the cohesive elements are used to account for the delamination at the [90/0] interfaces. Different progressive failure models employing fracture mechanics, continuum mechanics and micromechanics of failure are presented based on the MPDM-CE approach. The failure analyses by these progressive models are performed and their predictions are compared with the experimental results of notched [90/0]s CFRP composite. Reasonably good agreement between experimental results and simulation results is obtained and it is shown that the MPDM-CE approach can effectively predict the progressive failure of double-notched [90/0]s composite laminate.

Homogenization and Stress Analysis of Multilayered Composite Offshore Production Risers

An approach for stress analysis of multilayered composite cylinders is proposed for the analysis of new composite risers used in deep-water oil production of offshore petroleum industries. Risers essentially comprise long cylindrical sections connected end-to-end. In the formulation, only stresses and strains that are continuous through the thickness of the multilayered composite risers are taken to be equal to reported solutions for homogenous orthotropic hollow cylinders using homogenized material properties. These stress and strain solutions are then used to calculate the remaining discontinuous stresses and strains from the material properties of individual layers of materials. The homogenized elastic constants of cylindrically orthotropic composite risers are derived from forcedeformation equivalence, taking into account the stress and strain distributions in each layer. Four typical loading conditions are considered in the stress analysis, namely, internal and external pressures, axial loading, bending, and torsion. Examples of homogenized elastic constants and stress analyses of composite cylindrical structures with different layups and materials are presented to demonstrate the application of the proposed method. The results compared very favorably with those from other solutions. This method provides practical benefits for the design and analysis of composite risers. Because there is no requirement to explicitly enforce interfacial continuity in this method, stress analyses of composite cylinders with many layers of different fiber angles or materials can be carried out efficiently. The homogenized elastic constants can greatly expedite the analysis of entire composite riser systems by replacing complex models of riser sections with homogenized riser sections. [DOI: 10.1115/1.4024695]

Global-Local Analysis of a Full-scale Composite Riser during Vortex-Induced Vibration

This paper presents a global-local analysis procedure to demonstrate the feasibility of a composite riser and its advantages over the traditional steel counterpart. This procedure starts from the local design of the sandwich tubular structure of riser section. The equivalent material properties of the sandwich tube are obtained using classic composite theory and they are used to parameterize the full-scale riser model in global analysis. The global analysis mainly focuses on the vortex-induced vibration (VIV). The methodology is first verified by comparison with experimental data and results produced by SHEAR 7. Four representative cases are then studied and the results show that the critical loads experienced by the composite riser are much lower than that of the steel one due to its lightweight. The lightweight composite riser requires lower top tension and fewer buoyancy cans, which is economically beneficial. The failure envelopes of both composite and steel riser sections are obtained by performing damage modelling techniques. The results show that composite riser yields larger safety margin. Overall, this paper demonstrates that composite riser is technically feasible and its high performance/weight ratio would make it a promising design for deepwater environment, where self-weight is a big challenge that is hindering the development of traditional steel riser.Copyright