I am looking for FEM framework for cold cracks prediction in additive manufacturing. How to establish numerical criteria?
Good day! Today, most of the criteria for assessing the susceptibility to cold cracking are more qualitative than quantitative. To quantify the susceptibility for cold cracking, the characteristics of a specific material must be taken into account. The classical approach to assessing the probability of the nucleation of such defects is the simultaneous fulfillment of three conditions, namely, the presence of quenching structures (for steels, for example, the martensite content is often taken to be greater than 50 %), tensile stresses, and the presence of diffusible hydrogen. Depending on the type of metal, the critical hydrogen concentration and the maximum allowable stresses are determined. For the case of specific brittle materials (eg intermetallics), it is sufficient to use only the tensile stress level. Based on the experience of finite element modeling, I can add that with a small spatial partition (less than 1 mm), it is necessary to consider the fulfillment of these criteria in an area large enough for the formation of a macrodefect.
Alexey Milenin Thankyou for your answer, however, I wonder if it possible to estimate cold cracks in Molybdenum PBF with residual stress through FEM simulation? need your kind guidance
Good day! For your case, the principle of assessing the susceptibility to cold cracking is similar, namely, consideration of three factors: stress state, structural state and concentration of interstitials. If the assessment of the stress field for temperatures below 300 °C up to operating temperatures does not fundamentally differ from other materials or technologies, then nitrogen and oxygen should be considered as harmful impurities. Their diffusion, taking into account the different solubility in the liquid and solid phases, should not lead to the concentrations of more than 0.0001 (O) and 0.0005 (N). The structural factor is more complex and is associated with the growth of molybdenum grains - large grains significantly embrittle the metal. For to predict the grain size, cooling rates should be considered in the temperature range of normal grain growth. But here it is necessary to take into account the peculiarities of the specific technology.
Thank you so much. May I ask for relevant literature and case studies?
Muhammad Qasim Zafar , these problems are common and fundamental, so you can find them in welding theory books and molybdenum welding guidelines. Good luck!
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