VOL. 8 September ISSUE YEAR 2007
in Vol. 8 - September Issue - Year 2007
An Interest In The Fatigue Of Metals
Michele Bandini, General Manager of Peen Service s.r.l
Michele Bandini has a PhD in Mechanical Engineering and teaches at the Mechanical Engineering University of Bologna. He is also the General Manager of Peen Service s.r.l. MFN published an interview with him in the last March issue and would here like to continue the dialogue with this intriguing personality.
(?) MFN: Hi Michele, here we are again! Last time you spoke to us about the research in Peen Service. Could you tell us more about your studies on fatigue?
(!) M.B.: During my university studies, as a mechanical engineer, I dealt with fatigue of metals. I was really fascinated by that phenomenon and I decided to direct the studies exactly on fatigue. I learned all about cyclic loads, Woheler diagrams, knotch and stress concentration factors, etc. etc. I was a student and I was convinced that everything could be evaluated and taken into account through fatigue calculation. Unfortunately the reality is much too complicated to be confined to a pool of simple parameters. Nowadays we have very powerful computers that can handle hundreds of parameters and carry out billions of calculations in a few seconds. Nevertheless we still have fatigue failures. What a wonderful thing, we still need human contribution! All our efforts are in that direction. In more than fifteen years work we did a lot of research, and we will do much more in the future. We have two big activities always open. One is a university large base research, the other one is a research into our customers’ specific problems. We can apply the results of our large base research to solve the specific problems of our customers and those last ones stimulate further large base research. We learned really a lot finding solutions for our customers’ problems. Working with them enables us to be one step beyond their needs. These two activities have a great synergy on our knowledge.
(?) MFN: It seems really interesting. What kind of research are you investigating?
(!) M.B.: In the last years we have been trying to evaluate the effect of residual stress and crystallographic distortion on fatigue life. Nowadays residual stress is considered the most important parameter to predict fatigue life by many designers. We are convinced that it is a very important parameter but not the only one. In our laboratory we have an x-ray diffractometer, and many years spent doing residual stress measurements showed us that the risk of over-peening by too high intensity or excessive coverage is always around the corner. Normally the idea is the greater the problem, the harder the peening. Unfortunately it is not so simple. All metallic materials have their own capacity to absorb plastic deformation. If you go over that point you begin loosing benefits and, if you over-peen, you could have a real surface damage. The best you can do is understand the real problem and do exactly what you need where you need. Understanding the problem could appear quite simple but many times you can only look at the final breakage. Passing from the final breakage to the cause of the damage is not always a simple matter. That is the reason why we work with our customers, we study the failure with them and finally we support them in finding the best solution for their specific problem
(?) MFN: A very scientific approach for such a small company! How many of you are involved in this activity?
(!) M.B.: You are right. We are a small company, only fourteen but very motivated and enthusiastic people. Actually all of us are involved in this activity. We use our production machines also for research, and the results are shared with all our operators. If you want to do a nice job you must have consciousness on what you are doing.
We at MFN would like to thank Mr. Michele Bandini for this interview.