Puneet Mahajan

Effect of whole-body vibration on the low back. A study of tractor-driving farmers in north India.

STUDY DESIGN A retrospective cohort study of tractor-driving farmers (study group) and non-tractor-driving farmers (control group) matched for age, gender, generic/ethnic group, land-holding, and work routines. OBJECTIVES To determine, using magnetic resonance imaging and clinical investigations, the effect of whole-body vibrations on the back in tractor-driving farmers. SUMMARY OF BACKGROUND DATA Low back pain and pathologic changes in the lower backs of tractor drivers have been reported. However, no study with a control group matched for work-related risk factors has been reported. METHODS Fifty tractor-driving farmers were compared with 50 non-tractor-driving farmers matched for age, gender, ethnic group, land-holding, and work routine. Both groups were interviewed for details of work routine, assets held, family profile, and vibration exposure to assess the influence of these parameters on signs and symptoms of backache. Magnetic resonance imaging was done to assess the effect of exposure on whole-body vibration and degenerative changes in the back. Vibration measurements also were done on tractors to observe the actual severity of the vibrations. RESULTS Regular work-related backache was more common among tractor-driving farmers (40%) than among non-tractor-driving farmers (18%, P = 0.015). Anthropometric evaluation showed abdominal girth and weight to be significantly higher in tractor-driving farmers (P = 0.006 and 0.046, respectively), whereas while height and arm span were similar between the two groups. Clinical examination for evidence of disc or facet degeneration showed no difference between the two groups. Evaluation of magnetic resonance images of tractor-driving farmers and non-tractor-driving farmers by an orthopedic surgeon, radiologist, and neurosurgeon showed degenerative changes to be similar between the two groups (P > 0.050). CONCLUSIONS Tractor-driving farmers report backache more often than non-tractor-driving farmers, but no significant objective differences on clinical or magnetic resonance imaging evaluation were found between the two groups.

MACHINING STUDIES OF UD-FRP COMPOSITES PART 2: FINITE ELEMENT ANALYSIS

ABSTRACT A number of parameters and an exhaustive material development and experimental procedure to determine the response variables like cutting forces, surface damage restricts the expensive experimental research. In this context, Finite Element Method (FEM) analysis can be used as a tool for the prediction of the various machining responses. A finite element analysis of the orthogonal machining of Uni-directional Glass Fiber Reinforced Plastic (UD-GFRP) laminates is presented in this study to understand the complex relation between fiber orientation, tool geometry, depth of cut on cutting forces and sub-surface damage.

A parametric study of the impact response and damage of laminated cylindrical composite shells

The impact response and the resulting damage of laminated composite shell objects by a metallic impactor are studied by means of the finite-element method. The effects of important problem parameters, such as impactor mass and velocity, shell curvature and stacking sequence of plies, are established. The impact force and the structural response accounting for large deformations are examined for the case of a cylindrical curved panel. Impact-induced damage, viz. matrix cracking and delaminations, are predicted by the use of appropriate failure criteria and the damaged regions are plotted. The stiffness matrix is modified during each time step to take account of this damage. The effect of other ambient factors such as the presence of an initial stress on the impact response in a full cylinder are also examined. Hertzs contact law is used to calculate the contact force between the impacting mass and the shell.

Determination of Machining-Induced Damage Characteristics of Fiber Reinforced Plastic Composite Laminates

Abstract Machining of fiber reinforced plastic (FRP) components is often needed in spite of the fact that most FRP structures can be made to near net shape. The material removal mechanism of FRP is very difficult as compared with metals due to their inherent inhomogeneity and anisotropy. This results in frequent fiber pullout, delamination, matrix burning, and other damages leading to poor cut surface quality. A finite element model is proposed to quantify the material damage, which has been experimentally validated by means of nondestructive dye-penetrant testing. Good agreement is observed for laminates with fiber orientations up to 60°. Divergence is noticed for higher fiber orientations, and the discrepancies increase with increasing fiber orientation. Proper interfacial properties vis-à-vis machining of FRP materials are considered to be the main reasons for the divergence.

MACHINING STUDIES OF UNI-DIRECTIONAL GLASS FIBER REINFORCED PLASTIC (UD-GFRP) COMPOSITES PART 1: EFFECT OF GEOMETRICAL AND PROCESS PARAMETERS

ABSTRACT Secondary manufacturing processes such as machining is often needed to impart dimensional tolerance and assembly requirements to Fiber Reinforced Plastic (FRP) components despite the numerous difficulties encountered. Sub-surface damages in FRP products and reduction of product life due to machining is a new challenge for the industry and academia alike. Research works are underway to design suitable cutting tools in order to minimize these problems. The present study tried to investigate the various effects of geometrical and process parameters on the machining characteristics of UD-GFRP composites. The results of the study are analyzed in terms of chip formation observation, cutting forces and sub-surface damage.

Adaptive computation of impact force under low velocity impact

Abstract A simple and computationally efficient adaptive finite element analysis strategy has been adopted for accurate and reliable evaluation of contact force under low velocity impact. Contact of a spherical and cylindrical impactor on isotopic plates is considered. Adaptive mesh refinement enables the finite element mesh to be obtained automatically and the refined meshes influence the calculated contact force. Velocity and mass of impactor has some influence on discretization error as the discretization error changes with the change of these parameters.

Reliability Analysis of a Composite Plate under Low-Velocity Impact using the Gaussian Response Surface Method

A 3-D explicit dynamic finite element analysis is performed to determine the contact force and displacement between the impactor and the target. The uncertainties associated with the properties of the composite material, loading condition, and assessment of critical stresses affect the failure limit state to a greater extent. The Gaussian response surface method is used to predict the probability of failure. It is found that the system probability of failure is influenced more by delamination than the failure due to matrix cracking. Shear strength (T12) and Youngs modulus (E1 and E3) are the most sensitive parameters to influence the composite plate reliability.

Contact behavior of an orthotropic laminated beam indented by a rigid cylinder

Abstract A finite-element study of the contact behavior of laminated beams has been carried out. The influence of various parameters such as ply orientation, beam thickness, indenter size, presence of a compliant layer and the presence of matrix cracks and delamination on the contact behavior of a symmetric orthotropic laminate is studied. The results are expressed in terms of contact pressure distributions and force/indentation graphs. While laminate thickness, indenter size and the presence of a compliant layer affect the force/indentation behavior and pressure distributions, delamination seems to affect only the latter. Delaminations in the lower half, away from the contact regions, have an insignificant effect on contact behavior. Stacking sequence, except for the all 90 ° laminate, does not influence the contact behavior.

Digital Image Correlation of Low-Velocity Impact on a Glass/Epoxy Composite

Low-velocity-impact experiments were performed on a unidirectional laminate [0°]8 and cross-ply laminate [0°/90°]4 of E-glass/epoxy composite of thickness of 6.4 mm for incident energies 6.9 J, 9.48 J, and 12.7 J. The energy, contact forces, and displacement plots with respect to time are studied for a drop test. The damage observed as a back face signature on the back face of both cross-ply and unidirectional laminate are plotted. The composite was speckled randomly and the impact phenomenon was recorded using a high-speed camera. The DIC data were analyzed to obtain displacement and strains on the surface of the plate.

Numerical simulation of failure in a layered thin snowpack under skier load

Abstract Fracture initiation and propagation in a snowpack due to compressive and shear loads, generated by the self-weight of the snow and a skier, is modeled. The snowpack has three layers, with a weak layer sandwiched between two strong layers. The height of the snowpack above the weak layer is such that failure occurs only because of additional stresses generated by the skier. A static analysis is performed to determine stresses due to the self-weight of snow, followed by an explicit dynamic analysis to determine additional stresses and subsequent failure due to skier load. The failure is either due to interface crack growth or due to middle-layer failure accompanied by slope-normal displacements. The former is modeled using cohesive elements, while a softening stress–displacement relation is used for the latter. Both mechanisms are active in the snowpack, although one may be predominant depending on slope angle, shear strength and interface energy.