Prediction of fracture limits of IN625 alloy by coupling ductile damage models and anisotropic yielding functions with the classical Marciniak and Kuczyński model

The fracture forming limit diagram (FFLD) is gaining special attention in high strength materials where the necking tendency rarely occurs during sheet metal forming processes. In the present work, the classical Marciniak and Kuczyński (MK) model has been modified by coupling it with different ductile damage models (Cockcroft and Latham, Brozzo, Oyane, Ko, Oh, Rice and Tracey, McClintock and Clift) and anisotropic yielding functions (Hill 1948 and Barlat 1989) to predict the fracture limits of Inconel 625 (IN625) alloy at different temperatures. Firstly, uniaxial tensile testing has been conducted for the determination of important mechanical properties. Consequently, stretch forming experiments have been performed to analyze the forming limits of a material. It has been found that the safe and fracture forming limits of the material increased by approximately 17.26% and 22.22%, respectively, on increasing the temperature from 300 to 673 K. From the comparative analysis of different combinations of ductile damage models and yielding functions, the Cockcroft and Latham (C-L) damage model in combination with the Barlat 1989 yielding function helped in best predicting the theoretical FFLD as it displayed the least average root mean square error (RMSE) of 0.033. The other ductile damage models used for predicting the theoretical fracture limits displayed large error; hence, they should not be considered while designing a critical component in the manufacturing industry using IN625 alloy.

Anisotropic Yield Criterion of Rolled AZ31 Magnesium Alloy via Nanoindentation

In this paper, the anisotropic mechanical properties of rolled AZ31 magnesium alloys are investigated using nanoindentation tests at room temperature. Nanoindentation was carried out at four angles, including the rolling direction (0°), diagonal direction (45°), transverse direction (90°), and vertical direction (ND). Experimental results show that hardness increases as the rolling angle increases from 0° to 90° and is lowest in the ND direction. The hardness independent of the effect of indentation depth is obtained by analyzing the indentation size effect and then converting hardness values into yield strengths. A new criterion is proposed on the basis of the Hill48 yield criterion. The data obtained through the above experiments are used to determine the parameters in the new criterion. Finally, a solution to the challenge of modeling a function that accurately describes the anisotropic yielding behavior of AZ31 magnesium alloys is proposed using the nanoindentation technique to solve the requirements of specimen size and experimental methods of the macro test.

Settlement analysis of friction piles in consolidating soft soils

The paper shows how axisymmetric finite element numerical models can be used to optimize the design of friction piles foundations in an environment that is prone to regional subsidence. The study considers friction piles in typical Mexico City soft clays, that are subjected to external loads and soil consolidation due to variations in piezometric conditions. The constitutive models used to numerically simulate the behavior of the clays vary from a basic elastic perfectly-plastic model to a critical state model that is able to account for the anisotropic yielding behavior of Mexico City clay. The simulations consider the long term behavior of the internal piles within a large pile group.