Browsing by Author "Rashid, Faizan Md."

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Constraint Effects Using a Stress-state Dependent Cohesive Mode
(Elsevier, 2014) Rashid, Faizan Md.
In the present work, constraint effects on growth curves of a mode-I crack are determined using a triaxiality dependent cohesive model. Plane strain elastic-plastic analysis based on the modified boundary layer formulation is performed and for modeling the fracture process, the cohesive parameters and the mechanical properties for a mild steel are taken from literature. From the analysis, the resistance curves for a range of constraint parameter are obtained. A discussion is developed on the effectiveness of the triaxiality dependent model in capturing the well-known effect of constraint and also on the effect of the two model parameters on the resistance curves.
Constraint Effects Using a Stress-state Dependent Cohesive Model
(Elsevier, 2014) Rashid, Faizan Md.
In the present work, constraint effects on growth curves of a mode-I crack are determined using a triaxiality dependent cohesive model. Plane strain elastic-plastic analysis based on the modified boundary layer formulation is performed and for modeling the fracture process, the cohesive parameters and the mechanical properties for a mild steel are taken from literature. From the analysis, the resistance curves for a range of constraint parameter are obtained. A discussion is developed on the effectiveness of the triaxiality dependent model in capturing the well-known effect of constraint and also on the effect of the two model parameters on the resistance curves.
Ductile Fracture Simulation in a Compact Tension Specimen Using a Triaxiality Dependent Cohesive Zone Model
(Taylor & Francis, 2014-04) Rashid, Faizan Md.
This article reports the results of numerical implementation of a recently proposed versatile cohesive law (TCZM) that incorporates triaxiality of the stress state explicitly in its formulation. TCZM was implemented numerically by devising user-defined elements in ABAQUS v 6.10 for a CT specimen geometry to replicate its fracture behavior as observed in experiments. The measured macroscopic force-deflection curve characteristics show a good agreement with the experimental observations, which illustrates the effectiveness of the TCZM.
Effect of ply orientation, staking sequence and notch geometry on the failure behaviour of glass fibre-reinforced epoxy composite laminates: A numerical investigation
(IOP, 2022) Rashid, Faizan Md.
A detailed numerical failure analysis was conducted for unidirectional glass fibre-reinforced epoxy composite laminates having an elliptical cut-out at the centre using Hashin's damage model. The major axis, a, of the elliptical cut-out was fixed while the minor axis, b, was varied in such a way, that its upper extreme represented a situation of the plate with a circular hole, while the lower extreme of it represented the presence of a sharp crack in the structure. For angle ply cases, plies oriented along the material direction predicted an ever-increasing load replicating an elastic analysis without any damage accumulation. Such exceptionally higher stiffness and resistance to deformation were much anticipated, as the uni-axial tensile load was applied along fibre direction which shares a large portion of the load in comparison to the matrix material. While the plies oriented perpendicular to the direction of the material behaved as the weakest stack-up sequence in resisting uni-axial tensile load. Multi-angle hybrid composites predicted uneven failure behaviour. For the different combinations of multi-angle layups and minor axis, b, different trends for peak loads were observed. Interestingly, extension-shear coupling was observed for a few configurations which were marginally negligible for others. The variation of opening stress along the transverse direction predicts some very interesting observations. For the higher value of b, the opening stress decreases as we moved away from the irregularity. However, the situation of a plate with a sharp crack (b → 0) showed the effect of crack tip blunting. Near the vicinity of the sharp crack, the opening stress first dropped, then picked up, and again kept on decreasing as we move away. The drop in the stress near the vicinity of the sharp crack is attributed to the blunting of the crack tip.
Effect of shape and obliquity of projectiles on the ballistic response of sandwich structures with carbon/epoxy face sheet subjected to low-velocity impact
(Elsevier, 2022) Rashid, Faizan Md.
Low-velocity ballistic analysis of sandwich structures having carbon/epoxy plate and 5083- H116 aluminium alloy as face sheet and honeycomb core respectively was conducted. Effect of obliquity and shape of the projectile on the ballistic parameters such as stress build-up and the displacement of the sandwich, variation in the velocity of the projectile during the impact and the strain energy accumulation of the whole system was studied. The effect of the shape and obliquity of the projectile impacting a sandwich structure is the central theme of the article. A sharp projectile striking the sandwich panel perpendicular develops a large stress build-up on the sandwich structure. However, like the obliquity and shape of the projectile changed the stress build-up showed a very uneven pattern. The importance of the effective area of the projectile in contact with the sandwich panel plays a more important role than the profile of the projectile. The high strength and stiffness of the carbon/epoxy composite face sheet, caused the projectiles to recoil for all the obliquity and shapes projectile. An important observation was made, whrevealedlled that the displacement of the neighbouring elements has an appreciable effect on the displacement of the impacting point. The neighbourhood undulation resulted in the non-zero displacement of the impact point starting from the beginning of the impact analysis. Carbon/epoxy composite showed a good strain energy absorption capacity before failure..Experimental validation of the numerical finding will be available to the reader in a short time.
An experimental investigation on the effect of montmorillonite nanoclay on the mechanical properties of Ti6Al4V titanium-based carbon fiber/epoxy laminates
(Wiley, 2025-03) Rashid, Faizan Md.
A detailed experimental investigation was carried out to examine the effect of montmorillonite nanoclay reinforcement on the tensile, flexural, and impact behavior of Ti6Al4V titanium-based carbon fiber/epoxy laminates. The phenomena of crack bridging, agglomeration, enhanced adhesion between the titanium-composite layer, and mechanical locking due to the presence of nanoclay affected the mechanical and energy absorption ability of the nanoclay-reinforced Ti6Al4V titanium-based carbon fiber/epoxy laminates. A high nanoclay concentration bridged the crack growth, which eventually helped localize the delamination to the impacting location alone. The agglomeration phenomena lowered the energy absorption of both low and high-weight percentages of nanoclay. At a moderate weight percentage, the nanoclay enhanced the adhesion between the titanium-composite layer and triggered the mechanical locking, leading to high energy absorption. Rapid preformation accompanied by petal formation and localized tearing was observed in the high-velocity impact test. Percentage escalation in impact energy was firmly in tune with the amount of nanoclay reinforcement in the matrix.
High-velocity ballistic response of AA 1100-H14 based carbon-fiber metal laminates: an experimental investigation
(Wiley, 2023-12) Rashid, Faizan Md.
A detailed experimental investigation was carried out for the high-velocity ballistic response of AA 1100-H14 based carbon-fiber metal laminates (FMLs). FMLs with different metal volume fractions and the same thickness of carbon-epoxy fiber laminates were tested to examine the surface and internal damage. The ballistic performance parameters, namely % escalation in absorbed energy, specific energy absorbed, ballistic limit, specific perforation energy, first cracking energy, and global deformation profile, were studied and a comparison was drawn with pure carbons fiber reinforced epoxy composite laminates. Despite having greater thickness, pure carbon fiber-reinforced epoxy composite laminates absorbed less impact energy than FMLs and failed catastrophically. For FMLs, the % escalation in the absorbed energy and the specific energy absorption kept increasing with the increasing impact velocity until the onset of perforation. Once the perforation started, both these parameters showed a decreasing trend. Thick FMLs absorbed a good amount of energy, leading to projectile recoil suffering minimal damage. The ballistic velocity, specific perforation energy, and first cracking energy on the front and rear face of FMLs layers showed an increasing trend. The minimum for the thinner and maximum for the thicker FMLs attributed to the large thickness and more metal volume fraction. Contrary to the large deformation of the impacting points, pure carbon fiber-reinforced epoxy composite laminates showed very minimal deformation as compared to FMLs. The brittle nature of the epoxy resin resisted the deformation to a large extent leading to less energy absorption.
Implementation and validation of a triaxiality dependent cohesive model: experiments and simulations
(Springer, 2013-03) Rashid, Faizan Md.
A recently formulated triaxiality dependent cohesive model for plane strain is implemented and its versatility is tested in simulation of ductile fracture of mild steel at different states of stress. The triaxiality dependent model was implemented as linear displacement formulation based elements whose constitutive behaviour was dependent on the stress-state of the neighbouring continuum element. By comparing the experimental data and predictions of corresponding plane strain simulations, the model parameters are estimated. The model is shown to be effective in reproducing characteristic features of the macroscopic response of both pre-cracked as well as geometries without a preexisting nominal defect. Since the model parameters are held constant for simulations at different stress-states, they are effectively material constants.
Numerical investigation on the effect of different face sheet materials and core designs on the ballistic response of sandwich structures under low-velocity impact
(Elsevier, 2022) Rashid, Faizan Md.
In the present article, a detailed numerical deformation and failure analysis of sandwiched structures with different face sheet materials and core design has been carried out. Different face sheets materials ranging from aluminium alloys to composites such as carbon/epoxy and kevlar/epoxy fixed on different types of core were analyzed. Sandwiched structure with aluminium alloy face sheet showed minimum deformation of the impacting point, large impactor recoil and least strain energy absorption. Whereas carbon/epoxy face sheet showed large deformation of the impacting point for all the core designs. Employing the carbon/epoxy face sheet, the impactor recoiled only with square and hexagonal core design while the strain energy absorption was minimum for square and maximum for circular core designs. Kevlar/epoxy face sheet also showed large deformation of the impacting point for all the types of honeycomb core designs. The impactor recoiled very minimally for square core design and there was no recoil for the hexagonal and circular core. Kevlar/epoxy face sheet showed maximum displacement of the impacting point and strain energy absorption for the circular core. Thus, it can be said that sandwiched structure with a carbon/epoxy face sheet appeared to be the best choice in terms of energy absorption during the impact. The present study showed improvement in ballistic behaviour of sandwich structure with composite face sheet as compared to metallic face sheet in terms of energy absorption.
On the role of triaxiality in mode-I resistance curves
(Springer, 2014-05) Rashid, Faizan Md.
Insight into the role of triaxiality in mode-I, plane strain resistance curves of a representative ductile metal has been gained. Growth of a macroscopic crack is simulated as per modified boundary layer formulation for a range of constraint parameter with the fracture process represented by a triaxiality dependent cohesive model. In contrast to the predictions by a fixed cohesive law, the study shows that by including the effect of triaxiality on the work of separation, the stick-slip nature or the non-uniformity in the rate of the crack growth and its manifestations on the plastic wake and fracture surface can be predicted that are closer to trends observed in experimental literature.
Simulation of fracture in a low ductility aluminum alloy using a triaxiality dependent cohesive model
(Elsevier, 2017-06) Rashid, Faizan Md.
In the simulation of the ductile fracture process in a low ductility aluminum alloy, the limitations of the current implementation of a stress-state dependent cohesive model are identified. Ductile fracture data was generated at moderate triaxiality with experiments on a range of notched bars while at high triaxiality in growth of a pre-existing mode-I crack in compact test specimens. In the corresponding finite element analysis, cohesive elements obeying a stress-state dependent cohesive law were introduced in the plane where material separation was expected to occur. By recognizing that the effect of model parameters is decoupled in fracture at moderate triaxiality, a procedure is outlined to determine the unique combination of model parameters that is shown to reproduce the experimental data for the entire range of triaxiality well. It is argued that the necessity of a plane strain core and its thickness is largely driven by the extent to which plastic deformation spreads during the growth of crack.