7/30/2019 PhD Overview

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Synergistic damage m echanics approach to fiber-reinforced composite laminates subjected tobending loads. Skills used: Thermo-mechanics, Continuum damage mechanics, Micro-mechanics,Fiber reinforced Composites, FEA and Abaqus.

Objective: To analyze the effect of subcritical damage (matrix cracks) on the stiffness degradationof fiber-reinforced composite laminates.

Obtained the stiffness damage degradation equations using the continuum damage mechanics

formulations (CDM) and couple stress theory.

Utilized the concepts of micro-damage mechanics (MDM) to obtain the Crack Opening

Displacements (COD) with numerical simulations toolAbaqus.

Obtained the Synergistic Damage Formulation equations (SDM) by combining the CDM and

MDM formulations.

Verified the SDM formulations using FEA simulations on a composite laminate with two distinct

damage modes.

Research objective: Composite laminates in aerospace and renewable energy applications aresubjected to a combination of loads which include in-plane stress and out of plane bending and

torsion load. When the loads cross beyond the tolerance limit the total failure does not happen

instantaneously, but starts with a sub-critical damage and progress to critical damage. Matrix

cracking is generally considered sub-critical damage and de-lamination is considered critical

damage.

The focus of the research is to determine the effect of flexure/bending modulus with increasing

sub-critical damage density. We assume that the crack spacing is uniform and the laminate

configuration is multi directional laminate.

Research procedure: Continuum damage formulation with the aid of thermo mechanics and couple-stress theory is used to get to a point of writing stiffness and damage relation. Essentially one will

have relations such as stiffness tensor at a particular damage density is equal to the summation of

stiffness at virgin state and damaged state. The unknowns in these equations are a few damage

constants, Constraint parameters, and the stiffness of material in damage and virgin state.

Damage constants can be obtained by using a reference laminate. Damage constant with the aid of

average crack opening displacements (this is in one sense working with micro damage mechanics).

And the stiffness matrices in damaged and virgin states can be obtained using FEA simulations.

This combination of CDM,MDM and FEA is coined as synergistic continuum mechanics approach.

This was coined by Dr. Ramesh Talreja.

Verification of the SDM was done using FE simulations at various crack densities.

Simulations: Abaqus Standard linear analysis was performed. Solid continuum elements were

used with transversely isotropic properties. These configurations at these crack densitieswere

used for analysis. Periodic boundary conditions were used for the representative volume element.