An efficient FE model for dynamic instability analysis of imperfect composite laminates

Chakrabarti, Anupam Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.3

An efficient FE model for dynamic instability analysis of imperfect composite laminates

Anupam Chakrabarti 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.3

Role of Virtual Reality in Balance Training in Patients with Spinal Cord Injury: A Prospective Comparative Pre-Post Study

Madhusree Sengupta,Anupam Gupta,Meeka Khanna,U. K. Rashmi Krishnan,Dhritiman Chakrabarti 대한척추외과학회 2020 Asian Spine Journal Vol.14 No.1

Study Design: Prospective comparative pre–post study. Purpose: To evaluate the effects of game-based virtual reality (VR) training program for trunk postural control and balance in patients with spinal cord injury (SCI) and to assess the results according to the motor completeness (severity) of lesions using the American Spinal Injury Association Impairment Scale (AIS). Overview of Literature: Training with VR based gaming has a role to play in improving balance in patients with SCI. Methods: Patients with SCI (traumatic and non-traumatic) for <6 months were included in this hospital-based study. Participants were divided into two groups: experimental group (EG) consisting 21 patients, and control group (CG) consisting 12. Both groups underwent the conventional rehabilitation program. An additional training with semi-immersive VR therapy was conducted 5 days a week for 3 weeks in the EG with the focus on balance rehabilitation using the “Rhetoric.” The outcome measures were the Berg Balance Scale (BBS), balance section of the Tinetti Performance-Oriented Mobility Assessment (POMA-B), and Functional Reach Score (FRS). Results: Both groups consisted of young participants (mean age, 28 and 30.5 years, respectively) and predominantly men (>80%). One-third of them had tetraplegia and two-third had paraplegia. Between-group analyses showed no statistically significant differences in the main effects between groups (p-value: BBS, 0.396; POMA-B, 0.238; FRS, 0.294), suggesting that the EG group did not show significant improvement in the trunk and posture at the end of training sessions than the CG group. Similarly, no significant difference was observed according to the severity (completeness) of SCI in the between-group analyses using the AIS (A/B vs. C/D). Conclusions: VR is an adjunctive therapy for balance rehabilitation in patients with SCI.

Elasto-plastic damage model considering cohesive matrix interface layers for composite laminates

Bibekananda Mandal,Anupam Chakrabarti 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1

A three-dimensional (3D) Finite element (FE)-based progressive damage model, which considers the interface matrix layer between two neighboring laminae as a layer of cohesive elements, is proposed to analyze laminated composite plates. An elasto-plastic damage model is integrated with the FE-based program ABAQUS that uses user-defined material subroutine. The present damage model includes fiber failure, matrix failure, and delamination effects. A cohesive zone model, which is available in ABAQUS and uses cohesive elements, is combined with the proposed model to address the delamination damage in the interface layers. 3D solid brick elements are used to model composite layers, and cohesive zone elements are used in between two composite layers to model the adhesive layers. The proposed model has been applied for the progressive damage simulation of AS4/PEEK composite laminates under in-plane and uniaxial tensile loading.

Impact behaviour of GFRP and Kevlar/epoxy sandwich composite plate: Experimental and FE analyses

Md. Muslim Ansari,Anupam Chakrabarti 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

In this paper, dynamic response of GFRP composite plate under ballistic impact has been studied by experimental tests and also by an efficient FE model. Material characterization of GFRP composite is performed as required for progressive damage analysis of laminate due to impact. Shock effect of impact is considered in the material modeling of composite plate. The influence of the target thickness on the ballistic performance of the composite plate is also studied by considering 3.12, 6.24 and 9.36 mm thick targets. Moreover, sandwich composite plate consisting of GFRP and Kevlar/epoxy in three different combinations of laminate layers is considered to obtain suitable combination for structural application that offer better penetration resistance. Damage pattern, contact force histories and stresses in composite plate are studied in addition to residual velocity and acceleration of projectile. Numerical results from present FE model in terms of residual velocities and damage patterns in composite plate show good agreement with the experimental results.

Finite element analysis of functionally graded sandwich plates under nonlinear sense for aerospace applications

M.N.A. GulshanTaj,Anupam Chakrabarti,R. Malathy,S.R.R. Senthil Kumar 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.3

Owing to the increase in demand for composite materials for different applications in aircraft structures, the nonlinear response of functionally graded ceramic-metal sandwich plates under mechanical loading is studied in the present research work. Geometric nonlinearity (GNL) is considered by Green-strain components and further assumes the form of von Kármán strains. It is ascertained that the effective mechanical properties vary through the thickness direction as a function of volume fraction of ceramic and metal constituents and obeys power law equation. Higher order displacement model proposed by Reddy is incorporated in the study to arrive for 2D isoparametric finite element C0 formulation. A nine node Lagrangian element is accomplished to model the assumed plate geometry. Different thickness schemes are proposed to model the sandwich plate with graded layer as core/ face sheets. Although the model can handle thickness scheme of any kind, results are exposed for four types of symmetric sandwich plates. Comparison statement between isotropic and graded plates is drawn in each case by appropriate selection of power law exponent value. The present investigation may be useful for design engineers/researchers to arrive for particular thickness scheme based on the results, while performing large deformation analysis of functionally graded sandwich plates (FGSP).

Behaviour of GFRP composite plate under ballistic impact: experimental and FE analyses

Md. Muslim Ansari,Anupam Chakrabarti 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.5

In this paper, experimental as well as numerical analysis of Glass Fiber Reinforced Polymer (GFRP) laminated composite has been presented under ballistic impact with varying projectile nose shapes (conical, ogival and spherical) and incidence velocities. The experimental impact tests on GFRP composite plate reinforced with woven glass fiber (0°/90°)s are performed by using pneumatic gun. A three dimensional finite element model is developed in AUTODYN hydro code to validate the experimental results and to study the ballistic perforation characteristic of the target with different parametric variations. The influence of projectile nose shapes, plate thickness and incidence velocity on the variation of residual velocity, ballistic limit, contact force-time histories, energy absorption, damage pattern and damage area in the composite target have been studied. The material characterization of GFRP composite is carried out as required for the progressive damage analysis of composite. The numerical results from the present FE model in terms of residual velocity, absorbed energy, damage pattern and damage area are having close agreement with the results from the experimental impact tests.

Bi-axial and shear buckling of laminated composite rhombic hypar shells

Abhay K. Chaubey,Shubham Raj,Pratik Tiwari,Ajay Kumar,Anupam Chakrabarti,K.K. Pathak 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.2

The bi-axial and shear buckling behavior of laminated hypar shells having rhombic planforms are studied for various boundary conditions using the present mathematical model. In the present mathematical model, the variation of transverse shear stresses is represented by a second-order function across the thickness and the cross curvature effect in hypar shells is also included via strain relations. The transverse shear stresses free condition at the shell top and bottom surfaces are also satisfied. In this mathematical model having a realistic second-order distribution of transverse shear strains across the thickness of the shell requires unknown parameters only at the reference plane. For generality in the present analysis, nine nodes curved isoparametric element is used. So far, there exists no solution for the bi-axial and shear buckling problem of laminated composite rhombic (skew) hypar shells. As no result is available for the present problem, the present model is compared with suitable published results (experimental, FEM, analytical and 3D elasticity) and then it is extended to analyze bi-axial and shear buckling of laminated composite rhombic hypar shells. A C0 finite element (FE) coding in FORTRAN is developed to generate many new results for different boundary conditions, skew angles, lamination schemes, etc. It is seen that the dimensionless buckling load of rhombic hypar increases with an increase in c/a ratio (curvature). Between symmetric and anti-symmetric laminations, the symmetric laminates have a relatively higher value of dimensionless buckling load. The dimensionless buckling load of the hypar shell increases with an increase in skew angle.