Fracture & Fatigue

Fracture Simulation

In computational fracture mechanics, cohesive zone model is a widely used model for simulating crack growth. A triaxiality dependent versatile cohesive zone element is developed which can predict initiation and growth of crack in crack and uncracked geometry under monotonic or cyclic loading.

Design of systems with dissimilar solids such as thermal barrier coatings, ceramic laminates, fibre-matrix composites, welds requires a better understanding of the factors that influence cracks near interface. Focus of the work was to evaluate the role of constraint on crack tip stresses for a crack normal to the interface between dissimilar solids.

Fracture of Bi-Material Solids

Plastic Anisotropy and Splitting in High Grade Steel

Stress Separation in Digital Photoelasticity

High grade pipe steels (such as X-100) are usually developed by controlling the microstructure thermomechanically. Often the manufacturing process leads to overall strong texture and microstructural banding at mid thickness. Our work involved characterization of plastic anisotropy and splitting phenomenon in X-100 pipe steel.

Photoelasticity by itself will not give individual stress components. Individual stress components can be evaluated in conjunction with either numerical or other experimental techniques. Sophisticated whole field stress separation methodology has been developed for 2D problems. Research is currently on to extend it for 3D problems.

Thermal Shock Resistance Enhancement

Usage of metals in high temperature applications is restricted because of its inability to withstand high temperatures. A relatively thin (0.5-1.5 mm) layer of thermal barrier coating on the metal substrate remarkably increases the thermal load bearing capacity. Spallation of the coatings is a concern which we address by introducing pre-cracks.

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Study of effects Of Surface Enhancement Processes on Plastic Strain, Work Hardening & Residual Stresses- An Overview

Fatigue cracks originate mostly from surfaces. Inducing compressive surface stresses is found to enhance the fatigue life of components. Among the various surface enhancement processes, this research mainly focuses on shot peening method. Extensive experimental research has been done in understanding the underlying mechanism of shot peening. Shot peening proves to be complex in evaluating the material response due to the inherent stochastic nature of several variables. The peening variables such as shot velocity, size, material, angle of impact etc produces different plastic strain while producing different residual compressive stresses. Numerical techniques such as finite Element method, and/or discrete element method are explored. The limitation of such methods comes from the number of shots simulated.

As a first step, a review paper is being carried on the anvil that explores current research level in understanding the theoretical prediction of shot peening. In parallel, simple numerical experiments are executed using ABAQUS such as

  • single ball simulation (with and without plasticity)
  • multi-ball simulation with different combination of ball impacts (with and without plasticity)
For Details Contact: B Baskaran, S M. Sivakumar and Om Prakash

Multi axial fatigue life prediction on caliper brake components

Every modern brake manufacturer is compelled to meet stricter requirements with time constraints during development of safety related components "Brakes". The design is required to be taking into account the cumulative damage caused to the part in the service load condition. Damage accumulation will lead to cause fatigue failure over a period of time. Durability design and analysis are important elements to achieve these objectives. To evaluate fatigue life of brake caliper parts, with use of service load histories and laboratory test data by forming suitable hypothesis. This will enable evaluating product liability, matching test loads to field loads, evaluating the risk and improving the shape of highly stressed parts. To develop S-N curve for brake carrier and know about the failure pattern of caliper carrier component fatigue test has planned in high frequency Resonator rig at various load levels (g levels).Ref fig:1 for SN curve.

It is planned to formulate a procedure for fatigue life prediction of a component using strain energy density based approach. The nature of brake carrier loading is in high cycle regime. In the strain energy density based method, the plastic strain energy density is used to evaluate number of cycles to failure in low cycle fatigue regime. For high cycle fatigue regime, the amount of plastic strain is small. So plastic strain energy density for life prediction in high cycle application is difficult. Total strain energy density comprised of both elastic and plastic strain energy density is used for calculating high cycle fatigue life.

Linear static analysis (FEA) on brake carrier was completed (Fig: 2). Critical parameter has to be evaluated from the analysis to apply for fatigue models.

  • single ball simulation (with and without plasticity)
  • multi-ball simulation with different combination of ball impacts (with and without plasticity)
For Details Contact:  S.Saravanakumar, A. Banerjee and S.M. Sivakumar