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INTRODUCTION
Crane hooks are the components which load in industries and constructional sites. Recently, excavators having a crane-hook are widely used in construction work sites. One reason is that such an excavator is are generally used to elevate the heavy convenient since they can perform the conventional digging tasks as well as the suspension works. Another reason is that there are work sites where the crane trucks for suspension work are not available because of the narrowness of the site. In general an excavator has superior maneuverability than a crane truck. However, there are cases that the crane-hooks are damaged during some kind of suspension works. From the view point of safety, such damage must be prevented. Identification of the reason of the damage is one of the key points toward the safety improvement. If a crack is developed in the crane hook, mainly at stress concentration areas, it can cause fracture of the hook and lead to serious accidents. In ductile fracture, the crack propagates continuously and is more easily detectable and hence preferred over brittle fracture. In brittle fracture, there is sudden propagation of the crack and the hook fails suddenly. This type of fracture is very dangerous as it is difficult to detect.Crane hooks are one of the important components used in industries to carry heavy loads, basically crane hooks are
designed with pulley elongated by rope or a chain. In this paper mathematical calculations are done by varying cross sections triangular, trapezoidal, and rectangular with constant area of cross sections for two differrent materials of steel,cast-iron analysis are evaluated.
Failure of Crane Hook
To minimize the failure of crane hook.The stress induced in it must be studied. Crane is subjected to continuous loading and unloading. This causes fatigue of the crane hook but the fatigue cycle is very low. If a crack is developed in the crane hook, it can cause fracture of the hook and lead to serious accident. In ductile fracture, the crack propagates continuously and is more easily detectible and hence preferred over brittle fracture. In brittle fracture, there is sudden propagation of the crack and hook fails suddenly. This type of fracture is very dangerous as it is difficult to detect.
Strain aging embrittlement due to continuous loading and unloading changes the microstructure. Bending stress and tensile stress, weakening of hook due to wear, plastic deformation due to overloading, and excessive thermal stresses are some of the other reasons for failure. Hence continuous use of crane hooks may in-crease the magnitude of these stresses and ultimately result in failure of the hook.
Methodology of Stress Analysis
The analysis is carried out in two phase: 1) Finite element stress analysis of an approximate (acrylic) model and its verification by photo elasticity theory.2)Analytical analysis assuming hook as a curved beam and its verification using Finite element analysis of the exact hook. To establish the finite element procedure a virtual model similar to the acrylic mode is prepared in ANSYS and the results of stress analysis are cross checked with that of photo elasticity. After establishing the procedure a virtual model similar to actual crane hook sample is cre- ated using CAD software and the results of finite element analysis are now verified with that of analytical method.
III. THEORETICAL ANALYSIS
Machine members and structures subjected to bending are not always straight as in the case of crane hooks, chain links etc., before a bending moment is applied to them. For initially straight beams the simple bending formula is applicable and the neutral axis coincides with the centroidal axis. A simple flexural formula may be used for curved beams for which the radius of curvature is more than five times the beam depth. For deeply curved beams, the neutral and centroidal axes are no longer coinciding and the simple bending formula is not applicable.
A. Curved Beam
A beam in which the neutral axis in the unloaded condition is curved instead of straight or if the beam is originally curved before applying the bending moment, are termed as “Curved Beams Curved beams find applications in many machine members such as c–clampers, crane hooks, frames of presses, chains, links, and rings.
B. Straight Beam
A beam is a straight structural member subjected to a system of external forces acting at right angles to its axis
. DESIGN AND ANALYSIS OF MODIFIED CROSS SECTIONED HOOK
The optimization is done by reducing the material with either having stress same or in its extreme limits. The mass and volume are reduced by reducing the material but an application remains same. The analysis of modified hook shows that stress is slightly increased compared to the standard hook by means of reducing the contact area but within limits i.e less than 250Mpa which means the design is safe and practically applicable. Fig 3 shows the comparison of cross sections between standard trapezoidal and modified hook