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چكيده انگليسي :

Effects of Compressive Stresses in Improving Performance of Dies and Machines Abdolmajid Rezaie am rezaie@me iut ac ir Date of Submission September 22 2013 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor M Farzin Prof farzin@cc iut ac ir Abstract With the development of manufacturing industry the need for structures to withstand higher loads has been increased Pre stressed structures under compressive pre loads offer solution in such cases Pre stressed created in these structures can resist the major or even full part of the working load The main goal is to improve the load carrying capacity in comparison with non prestressed structure which often has another benefit i e improvement of fatigue life by decreasing mean stress in loading and unloading cycles In the present research by reviewing methods of pre stressing cylindrical sections and non cylindrical sections the design of two main types of pre stressed structures were studied Various methods of pre stressing of structures and also means of pre stressing were studied and compared Closed form solutions available in literature were compared with finite element results for both cylindrical and non cylindrical sections and the two sets of results were shown to be in agreement For pre stressed layered dies as an example of pre stressed cylindrical sections pre stressing process and the stress state at working conditions were simulated using the following two methods In the first method simulation was based on modeling all layers and stress state of die state was considered during pre stressing process In this method pre stresses in the die body and layers were applied equally using equivalent thermal strains The results were shown to be in agreement with the analytical results In the second method layers are considered as a single part and pre stresses are applied by finding a uniform temperature field which is applied to the part that models all layers This temperature field is calculated by analytical equations In this method only the final state of die after pre stressing can be studied For pre stressed press body as an example of pre stressed non cylindrical section a preliminary mechanical design procedure is discussed By using results of this design simulation can be run to verify the safety of preliminary design The simulation is carried out first by a 2D model and considering layers as a whole part Results showed that this model was not accurate enough because the stiffness is overestimated when layers are modeled as a single part To improve this simple model layers were considered as separate parts and simulation was run again A comparison between results of single part modeling of layers and multi part modeling of them showed that there was a considerable difference and therefore modeling layers as separate parts was required It was also shown that there was no need to model all layers and several layers could be modeled as a part In fact a large number of wires were modeled as a single part and then the number of wires was decreased in each simulation until the results were shown to be independent of the number of wires In order to verify the assumption of 2D simulations 3D modeling of press body was also studied Again in 3D simulations layers were modeled as both one single part and several parts The results of 3D simulation were shown to be in good agreement with the 2D simulations of press body It can be concluded in such cases preliminary designs and simulations can be carried out using 2D layered model Keywords Pre stressed Structures Compressive Pre stress Finite Element Method Stress Analyses Mechanical Design PDF created with pdfFactory trial version www pdffactory com

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نقش ايجاد پيش تنش هاي فشاري در بهبود عملكرد قالب ها و دستگاه ها

سازه پيش تنش دار , روش اجزا محدود , تحليل تنش , طراحي مكانيكي