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    Research Experience
    Nov 2016 - Nov 2017
    Research Associate
    University of Bath · Department of Mechanical Engineering
    Bath, England, United Kingdom
    Jan 2013 - Sep 2013
    PostDoc Position
    University of Cambridge · Department of Engineering
    Cambridge, England, United Kingdom
    Jan 2009 - Oct 2009
    Research Associate
    The University of Manchester · Northwest Composites Centre
    Manchester, United Kingdom
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    Umer Hameed Shah
    Alessandra Treviso
    Yasir F Joya
    Muhammad Saif Ullah Khalid
    Zahur Ullah
    Usama Hameed
    K. Mahmood
    Sanjay M R
    M. Salman Siddiqui
    Muhammad Rizwan
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    Chris R Bowen
    Liaqat Ali
    Umer Hameed Shah
    W.U.H. Syed
    Ridwan Yahaya
    Paul M. Weaver
    Usama Perwez
    Alessandra Treviso
    Asim Shahzad
    Hafiz Ali
    Current research
    Projects (1)
    Project
    Responsible for conducting research on an EPSRC project “Analysis and Design for Accelerated Production of Tailored composites (ADAPT)”. The project will closely partner Bath (and Exeter) academics with the National Composites Centre, and industrial collaborators (Airbus, GKN & Chomarat) that span the airframe supply chain. ADAPT will enable production of elastically tailored composite components at rates suitable for the next generation of short range aircraft. Unique continuum models for manufacturing processes and new analysis-driven design principles for stiffness tailoring will be created. The team will focus effort on creation of new capability with underlying fundamental research. I will undertake experiments and modelling to establish the analytical prediction of performance. In the initial stage of the project, understanding and characterisation of failure modes related to various local defects and damage will be required. In the mid to late stages, this knowledge will support the derivation of design principles and subsequently the optimisation, manufacture, testing and post-test analysis of technology demonstrators
    Research
    Research Items
    This study introduces a unit cell-based finite element micromechanical model that accounts for correct post cure fabric geometry, in situ material properties and void content within the composite to accurately predict the effective elastic orthotropic properties of 8-harness satin weave glass fiber-reinforced phenolic composites. The micromechanical model utilizes a correct post cure internal architecture of weave, which was obtained through X-ray microtomography tests. Moreover, it utilizes an analytical expression to update the input material properties to account for in situ effects of resin distribution within yarn (the yarn volume fraction) and void content on yarn and matrix properties. This is generally not considered in modeling approaches available in literature and in particular, it has not been demonstrated before for finite element micromechanics models of 8-harness satin weave composites. The unit cell method is used to obtain the effective responses by applying periodic boundary conditions. The outcome of the analysis based on the proposed model is validated through experiments. After validation, the micromechanical model was further utilized to predict the unknown effective properties of the same composite.
    Single lap joints of woven glass fabric reinforced phenolic composites, having four different overlap widths, were impacted transversely using a hemispherical impactor with different velocities in the low velocity impact range. The resulting damage was observed at various length scales (from micro to macro) using transmission photography, ultrasonic c-scan and x-ray micro tomography (XMT), in support of each other. These experimental observations were used for classification of damage in terms of damage scale, location (i.e. ply, interfaces between plies or bond failure between the two adherends) and mechanisms, with changing overlap width and impact velocity. In addition, finite element analysis was used to simulate delamination and disbond failure. These simulations were used to further explain the observed dependence of damage on overlap width and impact velocity. The results from these experiments and simulations lead to the proposal of a concept of lower and upper characteristic overlap width. These bounds relate the dominant damage pattern (i.e. scale, location and mechanism) with overlap width of the joint for a given impact velocity range.
    Hybrid glass–carbon 2D braided composites with varying carbon contents are impacted using a gas gun by impactors of masses 12.5 and 44.5 g, at impact energies up to 50 J. The damage area detected by ultrasound C-scan is found to increase roughly linearly with impact energy, and is larger for the lighter impactor at the same impact energy. The area of whitening of the glass tows on the distal side corresponds with the measured C-scan damage area. X-ray imaging shows more intense damage, at the same impact energy, for a higher-mass impactor. Braids with more glass content have a modest increase in density, decrease in modulus, and reduction in the C-scan area and dent depth at the impact site, particularly at the higher impact energies. Impact damage is found to reduce significantly the compressive strength, giving up to a 26% reduction at the maximum impact energy.
    Experiments have been performed to investigate the damage mechanisms and failure modes of crossply CFRP laminates under pure tensile and pure compressive loading. Unnotched and notched crossply laminates were tested. Extensive splitting was observed prior to specimen failure for both pure tension and pure compression cases. This mode of damage was seen to have a profound effect on the strength and notch sensitivities of the specimens. Although notches were observed to greatly weaken the laminate, the reduction in strength was not proportional to the inverse of the stress concentration factor presented by the notch geometry. This was explained by the damage that had developed around the notch tips that acted to reduce the stress concentration at hand, and effectively strengthen the laminate specimens.
    This paper evaluates various 3D preforming strategies for tensile stiffness, strength and ILSS. Normalised to 50% fibre volume fraction, 3D woven, stitched and tufted laminates show similar trend; differences can be accounted for by the tow crimp and distortion during stitching. Robotic fibre placed, tufted samples exhibit highest tensile properties and good ILSS values.
    This paper relates to an upgraded Industrial tracked vehicle which was found with a failed Balance arm during disassembly. The failure analysis of an actual Balance Arms surface was carried out using Fractography and Non Destructive testing techniques to dig out the root cause. The analysis revealed microscopic signatures categorically pointing towards post failure surface mechanical damage. The factor causing to promote failure was improper manufacturing i.e. casting which was further attributed to MnS inclusions.
    (Note: forthcoming article accepted 2nd August 2016) In this paper the challenges are described in determination of compressive strength for 3D angle interlocked glass fabric reinforced polymeric composites (3D-FRPC). It makes use of both experimental investigation and finite element analysis. The experimental investigation involved testing both 2D and 3D-FRPC employing ASTM D6641/D6641M-14 and subsequent scanning electron microscopic (SEM) imaging of failed specimens to reveal the stress state at failure. This was further evaluated using laminate level finite element (FE) analysis. The FE analysis required input of effective orthotropic elastic material properties of 3D-FRPC, which were determined by customizing a recently developed micro-mechanical model. The paper sheds new light on compressive failure of 3D angle interlocked glass fabric composites, as only scarce data is available in literature about this class of materials. It showed that although the tests produce acceptable strength values the internal failure mechanisms change significantly and the standard deviation (SD) and coefficient of variance (COV) of 3D-FRPC comes out to be much higher than that of 2D-FRPC. Moreover, while reporting and using the test data some additional information about the 3D-fabric architecture, such as the direction of angle interlocking fabric needs to be specified. This was because, for 3D angle interlocking of fabric along warp direction, the strength values obtained in the warp and weft direction were significantly different from each other. The study also highlights that due to complex weave architecture it is not possible to achieve comparable volume fractions with 2D and 3D fabric reinforced composites using similar manufacturing parameters for the vacuum assisted resin infusion process. Thus, the normalized compressive strength values (normalized with respect to volume fraction) are the highest for 3D-FRPC when measured along the warp direction, they are at an intermediate level for 2D-FRPC and the lowest for 3D-FRPC, when measured in the weft direction.
    Continuously varying fibre angle across flat plates has analytically been shown to improve buckling performance by up to 60%. However, manufacture of such panels has so far used methods which have either high radius of curvature and low deposition rate (Continuous Tow Shearing) or low radius of curvature and medium deposition rate (Advanced Fibre Placement). Discrete Stiffness Tailoring (DST) is an alternative way of varying fibre angle to increase buckling performance that is compatible with current high rate deposition methods such as Advanced Tape Laying (ATL). DST uses discrete changes of angle within individual layers to effect variation in stiffness across a composite component at the cost of in-plane butt joints within layers. Two schemes of distribution are considered for tailoring stiffness across the width of a panel; (i) Half Seam; where half the layers in a laminate are subject to tailoring and (ii) Full Seam; where all layers are tailored. Compression testing of flat panels shows that DST can improve buckling stress for Full Seam by up to 16% for the simple example of redistributing material in a standard angle quasi-isotropic [±45/90/0]2S laminate. Comparison of experimental results with standard buckling analyses (FEA, VICONOPT) indicates that DST results are predictable within the bounds of error introduced by experimental boundary conditions. Although no compression strength reductions were apparent in compression testing, tensile testing of seamed regions shows that improved buckling performance comes at the cost of reductions in transverse strength for Half Seam and Full Seam schemes. However, such reductions should be acceptable where loading is compression dominated and seams run parallel to the load.
    Answer
    Selective Sub-Cycling is another option that you can use. This will be especially useful if only a small number of elements have a very small stable time increment and the rest have relatively large stable time increment. 
    Mass-scaling can also be useful but do check the Artificial Strain Energy in history output to make sure that the mass related forces are not contributing significantly to the model output. 
    Metal sheets have the ability to be formed into nonstandard sizes and sections. Displacement-controlled computer numerical control press brakes are used for three-dimensional sheet metal forming. Although the subject of vendor neutral computer-aided technologies (computer-aided design, computer-aided process planning and computer-aided manufacturing) is widely researched for machined parts, research in the field of sheet metal parts is very sparse. Blank development from three-dimensional computer-aided design model depends on the bending tools geometry and metal sheet properties. Furthermore, generation and propagation of bending errors depend on individual bend sequences. Bend sequence planning is carried out to minimize bending errors, keeping in view the available tooling geometry and the sheet material properties' variation. Research reported in this article attempts to develop a STEP-compliant, vendor neutral design and manufacturing framework for discrete sheet metal bend parts to provide a capability of bidirectional communication between design and manufacturing cycles. Proposed framework will facilitate the use of design information downstream at the manufacturing stage in the form of bending workplan, bending workingsteps and a feedback mechanism to the upstage product designer. In order to realize this vendor neutral framework, STEP (ISO 10303), AP203, AP207, and AP219 along with STEP-NC (ISO14649) have been used to provide a basis of vendor neutral data modeling.
    This study introduces a unit cell-based finite element micromechanical model that accounts for correct post cure fabric geometry, in situ material properties and void content within the composite to accurately predict the effective elastic orthotropic properties of 8-harness satin weave glass fiber-reinforced phenolic composites. The micromechanical model utilizes a correct post cure internal architecture of weave, which was obtained through X-ray microtomography tests. Moreover, it utilizes an analytical expression to update the input material properties to account for in situ effects of resin distribution within yarn (the yarn volume fraction) and void content on yarn and matrix properties. This is generally not considered in modeling approaches available in literature and in particular, it has not been demonstrated before for finite element micromechanics models of 8-harness satin weave composites. The unit cell method is used to obtain the effective responses by applying periodic boundary conditions. The outcome of the analysis based on the proposed model is validated through experiments. After validation, the micromechanical model was further utilized to predict the unknown effective properties of the same composite.
    Answer
    FE micromechanics can be handled equally well by most general purpose  FE software like ABAQUS, Comsol, Ansys. But if you are looking for analytical micromechanics than probably you can use a simple tools like CADEC or MicMac etc. 
    The failure mechanisms and failure stress states of 2D and 3D FRP composite is investigated through experimental work, SEM, finite element analysis and failure theories. In this research work, feasibility of ASTM standard D6641 is investigated for testing of 3D FRP composite. A 3D finite element model is developed in ABAQUS with homogeneous orthotropic laminate to investigate the failure stress state in the gage section of the test specimens. Two failure theories are considered for failure investigation that is fully interactive three dimensional Tasi Wu failure criteria and limit criteria (maximum stress criteria). SEM is carried out to investigate the failure mechanisms and failure location in the specimens. Experimental results shows that the compressive strength of 3D FRP composite is less as compared to 2D FRP composite, also standard deviation (SD) and coefficient of variance (COV) of 3D FRP composite is high. This paper highlights the problems associated with the use of ASTM D6641 for 3D FRP composite, and internal failure mechanisms in 3D FRP composite using compression through combine end and shear loading.
    Single lap joints of woven glass fabric reinforced phenolic composites, having four different overlap widths, were impacted transversely using a hemispherical impactor with different velocities in the low velocity impact range. The resulting damage was observed at various length scales (from micro to macro) using transmission photography, ultrasonic c-scan and x-ray micro tomography (XMT), in support of each other. These experimental observations were used for classification of damage in terms of damage scale, location (i.e. ply, interfaces between plies or bond failure between the two adherends) and mechanisms, with changing overlap width and impact velocity. In addition, finite element analysis was used to simulate delamination and disbond failure. These simulations were used to further explain the observed dependence of damage on overlap width and impact velocity. The results from these experiments and simulations lead to the proposal of a concept of lower and upper characteristic overlap width. These bounds relate the dominant damage pattern (i.e. scale, location and mechanism) with overlap width of the joint for a given impact velocity range.
    Single lap joints of woven glass fabric reinforced phenolic composites, having four different overlap widths, were impacted transversely using a hemispherical impactor with different velocities in the low velocity impact range. The resulting damage was observed at various length scales (from micro to macro) using transmission photography, ultrasonic c-scan and x-ray micro tomography (XMT), in support of each other. These experimental observations were used for classification of damage in terms of damage scale, location (i.e. ply, interfaces between plies or bond failure between the two adherends) and mechanisms, with changing overlap width and impact velocity. In addition, finite element analysis was used to simulate delamination and disbond failure. These simulations were used to further explain the observed dependence of damage on overlap width and impact velocity. The results from these experiments and simulations lead to the proposal of a concept of lower and upper characteristic overlap width. These bounds relate the dominant damage pattern (i.e. scale, location and mechanism) with overlap width of the joint for a given impact velocity range.
    Numerical simulations for composite structure with stress concentration (e.g.:hole, slit) have been conducted under simple loading (ex. tensile loading), but rarely have been conducted under combined loading. In this study, strength tests of plane specimen with a slit under combined loading (tension and shear) and observation were conducted. Furthermore, numerical simulations considering both in-plane and interlaminar failure were also conducted to investigate the failure mechanisms. Detail observation showed difference of failure mode according to loading pattern. Numerical simulations showed good agreement with failure mechanism. Furthermore, failure load was predicted in various loading patterns with practically sufficient accuracy by use of band broadening stress as compressive strength.
    Experiments have been performed to investigate the damage mechanisms and failure modes of crossply CFRP laminates under pure tensile and pure compressive loading. Unnotched and notched crossply laminates were tested. Extensive splitting was observed prior to specimen failure for both pure tension and pure compression cases. This mode of damage was seen to have a profound effect on the strength and notch sensitivities of the specimens. Although notches were observed to greatly weaken the laminate, the reduction in strength was not proportional to the inverse of the stress concentration factor presented by the notch geometry. This was explained by the damage that had developed around the notch tips that acted to reduce the stress concentration at hand, and effectively strengthen the laminate specimens.
    Hybrid glass–carbon 2D braided composites with varying carbon contents are impacted using a gas gun by impactors of masses 12.5 and 44.5 g, at impact energies up to 50 J. The damage area detected by ultrasound C-scan is found to increase roughly linearly with impact energy, and is larger for the lighter impactor at the same impact energy. The area of whitening of the glass tows on the distal side corresponds with the measured C-scan damage area. X-ray imaging shows more intense damage, at the same impact energy, for a higher-mass impactor. Braids with more glass content have a modest increase in density, decrease in modulus, and reduction in the C-scan area and dent depth at the impact site, particularly at the higher impact energies. Impact damage is found to reduce significantly the compressive strength, giving up to a 26% reduction at the maximum impact energy.
    Paper looks at the effect of glass content on impact performance of glass/carbon hybrid braid. C-scan of the damage area was smaller for heavier impactor, at equal impact energies (IE). Residual dent increases linearly with impact energies, except three severely damaged samples. Significant proportion of the impactor energy is transferred to elastic energy in plate. Modal analysis gives efficient way of modelling interaction between impactor and plate. Effect of inelastic behaviour at contact is modelled by an effective contact compliance.
    This paper evaluates various 3D preforming strategies for tensile stiffness, strength and ILSS. Normalised to 50% fibre volume fraction, 3D woven, stitched and tufted laminates show similar trend; differences can be accounted for by the tow crimp and distortion during stitching. Robotic fibre placed, tufted samples exhibit highest tensile properties and good ILSS values.
    Single lap joints of woven GFRP composites have been investigated for impact induced damage modes using C-scan, X-ray micro tomography, imaging and finite element (FE) modelling. This has allowed for damage modes to be observed in 3D from macro to micro level-resulting in much better understanding of damage mechanisms and realistic FE modelling.
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