Analysis,Prediction And Experimental Study Of Composite Curved Surface Parts Distortion Under Residual Stresses

Traditional machining considers that the final shape of the part is produced by the enveloping motions of the cutter during machining without taking the complex physical processes of metal cutting into account.However,the actual cutting process is made up of a group of physical processes in which factors such as stress field,temperature field,plastic flow and phase change within the workpiece would affect the final shape of the part.The geometric deviations between the machined part and the cutter envelope surface caused by physical processes in the cutting process are called machining deformations.More specifically,those deformations are caused by the generation of surface residual stresses,the release of substrate residual stresses,cutting force,cutting heat,stiffness changes and clamping forces,etc.Recently,for the wide application of large parts and thin-walled parts in ship/offshore and aerospace industries,the phenomenon of machining deformation has got more and more attention.For the machining of controllable pitch propellers used in the offshore platforms,the generation of surface residual stresses and the release of base residual stresses are important sources of their machining deformations.Modeling and analyzing of those deformations are the basis of controlling them.This paper studies the modeling and simulation methods of residual stresses related machining deformations of large-scale parts such as the controllable pitch propellers used in the offshore platforms,the main work is as follows:The simulation method of machining deformations caused by the generation of surface residual stresses was studied.In order to overcome the shortcomings of the existing methods,a new method was proposed.In this new method,the concept of equivalent deformation force was proposed by deriving the basic differential equations of the deformation of elastomer with residual stresses.Based on the concept of equivalent deformation force,the complex deformations caused by surface residual stresses were simplified into simple elastic deformations under equivalent deformation forces.Therefore,the effective numerical calculation method of deformation prediction of large-scale surface parts was established and proved.To implement the proposed method,the calculating method for equivalent forces which could use the geometric information in the part CAD model as input was established based on the knowledge of tensor analysis and differential geometry.A software named SPDCT(Surface Processing Distortion Calculation Tool)was developed using C#language and the UG/Open API interface.The software can use the surface geometric information in the part CAD model to calculate equivalent forces of the surface residual stress field and then apply them to FE models(Abaqus INP file).Using the SPDCT software,the machining deformations of several typical parts were calculated.The example of flat plate showed that E.Brinksmeier's source stress method can be seen as a special case of the new method in case that the machining surface is flat and the introduced surface residual stress distributed uniformly.In the example of curved surface parts,the new method used only 1/58 nodes and 1/65 elements of the mapping method to solve the same deformation prediction problem.This could not only save computational resources but also make the new method can be used to predict the machining deformations of larger parts.The shot peening deformations of large controllable pitch propeller used in the offshore platform were calculated using the proposed method and verified by experiment.In the experiment,the shot peening residual stress field was calibrated by the source stress method.Use the geometric information in the part CAD model and the surface residual stress field calibrated,the shot peening deformations of the large controllable pitch propeller were predicted.By comparing the predicted results with the experimental data,the accuracy of the new method was verified.The simulation method of the deformations caused by the release of base residual stresses was studied and a new method for calculating those deformations was proposed.The new method equivalent the deformations caused by the release and redistribution of base residual stress field to simple elastic deformations under equivalent forces.To implement the proposed method,an Abaqus plug-in was developed.Compared with original methods,the new method needs only 2D residual stress field on the machined surfaces as input,which reduces the requirement and workload of base residual stress field modeling.Using the new method,the residual stress release deformations of several typical parts were calculated.To improve the reliability of residual stress modeling,the residual stresses in the blank were measured using both the crack compliance method and the contour method.By comparing the predicted results of the curved surface example with experimental data,the accuracy of the new method was verified.What is more,to counteract those machining deformations,the part CAD model was modified according to the deformation prediction results.The subsequent machining experiment showed that the modification of the part CAD model successfully suppresses the part's machining deformations.The machining deformation is only about 20%of the unmodified one.