Dmitry Ivanov

Bio: Dmitry Ivanov is an academic researcher from University of Bristol. The author has contributed to research in topics: Finite element method & Epoxy. The author has an hindex of 25, co-authored 94 publications receiving 2690 citations. Previous affiliations of Dmitry Ivanov include Katholieke Universiteit Leuven & Berlin School of Economics and Law.

A comparative study of tensile properties of non-crimp 3D orthogonal weave and multi-layer plain weave E-glass composites. Part 1: Materials, methods and principal results

Abstract: Composites fabricated by VARTM technology with the use of single-ply non-crimp 3D orthogonal woven preforms 3WEAVE ® find fast growing research interest and industrial applications. It is now well understood and appreciated that this type of advanced composites provides efficient delamination suppression, enhanced damage tolerance, and superior impact, ballistic and blast performance characteristics over 2D fabric laminates. At the same time, this type of composites, having practically straight in-plane fibers, show significantly better in-plane stiffness and strength properties than respective properties of a “conventional” type 3D interlock weave composites. One primarily important question, which has not been addressed yet, is how the in-plane elastic and strength characteristics of this type of composites compare with respective in-plane properties of “equivalent” laminates made of 2D woven fabrics. This 2-part paper presents a comprehensive experimental study of the comparison of in-plane tensile properties of two single-ply non-crimp 3D orthogonal weave E-glass fiber composites on one side and a laminate reinforced with four plies of plain weave E-glass fabric on the other. Results obtained from mechanical testing are supplemented by acoustic emission data providing damage initiation thresholds, progressive cracks observation, full-field surface strain mapping and cracks observation on micrographs. The obtained results demonstrate that the studied 3D non-crimp orthogonal woven composites have considerably higher in-plane ultimate failure stresses and strains, as well as damage initiation strain thresholds than their 2D woven laminated composite counterpart. Part 1 presents the description of materials used, experimental techniques applied, principal results and their mutual comparisons for the three tested composites. Part 2 describes in detail the experimentally observed effects and trends with the main focus on the progressive damage: detailed results of AE registration, full-field strain measurements and progressive damage observations, highlighting peculiarities of local damage patterns and explaining the succession of local damage events, which leads to the differences in strength values between 2D and 3D composites.

Experimental methodology of study of damage initiation and development in textile composites

Abstract: Damage in textile composites is closely connected with the internal micro- and meso-geometry of the reinforcement, and reveals features, which are not present in the damage processes in classical laminates. This paper proposes a test sequence intended to characterise damage in textile composites - its initiation and development different scale levels: (1) Tensile tests on samples cut in characteristic directions of the textile reinforcement (machine, cross and bias), accompanied with acoustic emission (AE) registration and full-field strain measurement on the surface. The test produces stress-strain diagrams and identifies characteristic strain levels for post-mortem investigation: just after first damage e 1 ; well-developed damage e 2 ; just before the final fracture of the sample e 3 . Full-field strain measurement highlights the relation between strain concentrations (linked with the damage initiation) and the reinforcement structure. (2) Samples loaded up to e 1...3 3 are examined with CT and X-ray. This reveals the damage pattern and allows quantitative characterising of the damage development. (3) Optical and SEM examination of cross-sections through the damage sites, determined with X-ray, identifies local damage modes. The same strain levels are further used for setting up fatigue tests. The experimental protocol is applied for triaxial braided and quasi-UD composites.

Full field strain measurements for validation of meso-FE analysis of textile composites

Abstract: Meso-scale (unit cell of an impregnated textile reinforcement) finite element (FE) modelling of textile composites is a powerful tool for homogenisation of mechanical properties, study of stress–strain fields inside the unit cell, determination of damage initiation conditions and sites and simulation of damage development and associated deterioration of the homogenised mechanical properties of the composite. Validation of meso-FE modelling requires registration of details of the deformed state on the scale of individual yarns inside the textile, registered using full-field strain measurements on the surface of the sample. The paper presents examples of such a validation of meso-FE models of woven (carbon/epoxy and glass/polypropylene) and braided (carbon/epoxy) composites. Digital image correlation and digital phase shifting grating shearography are used for full-field strain registration. The resolution of the strain field during elastic deformation is improved and damage onset is identified using time-dependent linear regression of the registered field.

Multiscale modeling of composite materials: a roadmap towards virtual testing

Abstract: A bottom-up, multiscale modeling approach is presented to carry out high-fidelity virtual mechanical tests of composite materials and structures. The strategy begins with the in situ measurement of the matrix and interface mechanical properties at the nanometer-micrometer range to build up a ladder of the numerical simulations, which take into account the relevant deformation and failure mechanisms at different length scales relevant to individual plies, laminates and components. The main features of each simulation step and the information transferred between length scales are described in detail as well as the current limitations and the areas for further development. Finally, the roadmap for the extension of the current strategy to include functional properties and processing into the simulation scheme is delineated.