COMPUTER MODELING OF FLOW LINES AND FLAW MIGRATION --- IN BULK DEFORMATION PROCESSES 1 I A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University In Partial Fulfillment of the Requirements for the Degree Master of Science NITIN V. HATTANGADY ,* - -"- November, 1987 ACKNOWLEDGEMENTS I take this opportunity to express my sincere gratitude to Dr. J.S. Gunasekera for the valuable guidance and assistance during the course of this project and my stay at Ohio University. I would also like to thank Dr. Shesh Srivatsa (GE- AEBG, Cincinnati, Ohio), Dr. Sulekh C. Jain (GE-AEBG, Cincinnati, Ohio), Dr. H.L. Gegel (WPAFB-MLLM, Dayton, Ohio) and Dr. J.M. Alexander (Stocker Visiting Professor, Ohio University) for their participation and suggestions during this project. September 1987 NITIN V. HATTANGADY TABLE .OF CONTENTS 1 . INTRODUCTION ...................................... 2 . PREFERRED ORIENTATION AND MECHANICAL FIBERING ..... 6 METAL INGOT STRUCTURE ......................... 7 EFFECT OF MECHANICAL WORKING ON THE METAL STRUCTURE ..................................... 10 DIRECTIONALITY OF THE MECHANICAL PROPERTIES DUE TO METAL WORKING ............... 25 3 . PROGRAM STRUCTURE AND DESCRIPTION ................. 30 IMPLEMENTATION OF FLOW LINES IN ALPID 2.0 .... 31 DESCRIPTION : PROGRAM FLINES ................. 35 POST PROCESSOR FLPLOT .......... 40 4 . VALIDATION OF THE SOFTWARE ......................... 52 FLOW LINE PLOTS FROM EXTRUSION SIMULATION ..... 53 5 . CONCLUSIONS ........................................ 62 6 . REFERENCES ......................................... 64 7 . APPENDIX A (USER'S MANUAL) ........................ 66 8 . APPENDIX B (SAMPLE RUN) .......................... 76 9 . APPENDIX C ........................................ 106 10 . APPENDIX D ....................................... 109 11. APPENDIX E : LISTING OF SAMPLE DATA FILES ........ 110 12. APPENDIX I?: ULTRASONIC NON-DESTRUCTIVE TESTING IN THE FORGING INDUSTRY ................... 115 --LIST OF FIGURES 1. Macrostructure of cast steel containing 0.8 % carbon .............................................. 9 2. Typical development of grain flow by plastic deformation of metals, (a) As consolidated, (b) As wrought, (c) Wrought and re-crystallized ......... 11 Macrostructure of deformed metal after forging ...... 4. Comparison of grain structures of forging, bar stock and casting ................................... 14 5. Deformation in compression of idealized equiaxed grains in a workpiece, such as is done in forging or rolling of metals. (a) Before, and (b) After plastic deformation .................. 17 6. Deformation of single crystals. (a) Slip in tension. As deformation progresses, the slip planes tend to align themselves in the direction of pulling. (b) Slip in compression. The slip planes tend to align themselves parallel to the plattens ............................ 18 7. A1ignment of Manganese Sulphide inclusions (thin dark elongated regions) in AISI 1215 steel leading to mechanical fibering. Magnification 100x .................................. 22 8. Schematic illustration of the deformation of soft and hard inclusions, and their effect on void formation in plastic deformation of metals ..... 24 9. Anisotropy in wrought metals, (a) development of ductility anisotropy, (b) nature of anisotropy ...... 27 10. Effect of forging reduction on longitudinal and transverse reduction in area ....................... 28 11. Flow chart fo the FLINES ALPID version ............. 38 12. Flow chart for the post processor FLPLOT ........... 44 13. Flow lines in the extrusion of cast billets - step 0 ............................................. 53 14. Flow lines in the extrusion of cast billets - step 40 ............................................ 54 15. Flow lines in the extrusion of cast billets - step 60 ............................................ 55 16. Flow lines in the extrusion of cast billets - step 110 ........................................... 56 17. Display of maximum strain directions in cast billets (step 110) ................................ 57 18. Flow lines in the extrusion of extruded billets -v- .step 0 ........................................... 58 19. Flow lines in the extrusion of extruded billets .step 40 .......................................... 59 20 . Flow lines in the extrusion of extruded billets .step 60 .......................................... 60 21. Flow lines in the extrusion of extruded billets .step 110 ......................................... 61 Chapter 1 INTRODUCTION One of the most important goals of any manufacturing organization is to produce defect free parts. Defect avoidance is critical for rotating parts such as an engine disk, and the ability to detect flaws having the characteristic of a flat bottom hole by ultrasonic inspection is absolutely essential. The ability to find such a flaw by ultrasonic inspection when a forged part is ensonified is determined by the Flow Line Theorem [5], which states that most defects will lie along flow lines and the sonic beam must be normal to the flow lines to maximize the ability to detect ideal flat bottom flaws. An empirical criterion says that the limit of detection is when the sonic beam makes an angle of 25 degrees with respect to the flow line normal [5]. New complex materials, with structural and high temperature applications in future aircraft systems, are being developed to meet specific needs. The processing of these expensive materials entails the use of special, expensive and complex metal forming operations in order to achieve the desired properties in the product. The application also imposes a requirement of using defect free parts. As a result of mechanical working, a certain degree of directional ity is introduced into the microstructure in 2 which the second phases and inclusions are oriented para1 lel to the direction of greatest deformation. When viewed at low magnification, this appears as flow lines or fiber structure. Flaws in a final forged component often originate and can be detected in the original billet. Hence, predicting the metal flow, orientations of the flow lines formed and/or the ability to model the migration of flaws would be an important capability in any metal forming simulation program. The location and the orientation of the flaws determines the directional properties of the formed part and hence, tracking the movement of the flaws would help in deciding whether the billet should be subjected to further processing. Thepreforned billets used in the forging industryare generally extruded and in some cases cast into the desired shape. Extruded billets have a fiber structure with the flow lines in the direction of applied force due to the extrusion operation. A further deformation operation would result in re-orientation of the existing flow lines. Cast billets, on the other hand, have an initial homogeneous structure and any metal forming operation results in a breakdown of the dendritic structure. The grains get elongated in the direction of greatest deformation, i.e., the direction of maximum principal strain to form a fibrous structure. The objective of this project was to develop a 3 computer program, linked with ALPID (Analysis of Large Plastic Incremental Deformation) [8,9], to predict the orientations of flow lines and to serve as a tool to improve the efficacy of the ultrasonic non-destructive testing technique used in the forging industry. A computer program, FLINES, with graphics capability has been developed and incorporated into the rigid plastic finite element program ALPID to predict the orientation of the flow lines and track the path of user specified material points at randomly oriented flaws. The module FLINES, developed in FORTRAN 77, provides two options viz., tracking user specified material points on flow lines of known orientations (as in extruded billets) or placing circles on the billet cross section and track their deformation (as in the case of cast billets). This program has been interfaced with the ALPID program version 2.0. A post processor, FLPLOT, with the capability of displaying the orientation of the flow lines before and after deformation, has been developed. The post processorhas the capabilty of displaying the gradual distortion of the finite element mesh placed on the initial billet geometry, if the nodes are being tracked. Additional features include tracing the path of a single point within the billet geometry through the entire metal forming process, and display of the magnitude and direction of the principal strain and the material rotations (in case of cast 4 billets). The post processor provides graphics display of the results on Tektronix 4000/4100 series terminals and compatibles and Intergraph Interact/Interpro32 workstations. An important feature of the post processor is the creation/update of the global flow lines data base which can be used to carry over the data through re- meshings and view the movement of the flow lines and migration of user specified material points during the entire simulation. The validation of the software has been carried out by simulating extrusion of a round to round section as an example problem. Extrusion has been used as the example problem because flow lines in extruded products are always oriented parallel to the direction of extrusion and hence the results would be self-validating. The software developed has been used successfully to predict flow line orientations formed in a complex forging. The experimental validation of the