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Applying the reliability concept as a new and profitable design approach can optimize the design and manufacturing of tillage machines. In this study, the Monte Carlo method was used to perform reliability analysis on the whole chassis of a moldboard plow. For this, a complete model of a three-bottom moldboard plow was assumed as the limit mode function. Stochastic soil parameters were applied and the interaction forces of the plow with soil were simulated with finite element method (FEM). The desired output was the soil reaction forces on the plow at the most critical plowing speed and depth. Then, by applying the forces obtained from the FEM model and considering Young's modulus of the chassis as a random variable, chassis static analysis was performed in different iterations and the stress concentration at different locations was determined. The probability of failure (Pf) and reliability index (β) of different locations of chassis were calculated. The results of the Monte Carlo simulation showed that the highest Pf occurred in crossbars, standards, braces and, masts with the values of 1, 0.296, 0.165 and, 0.033, respectively, which indicates the uncertainty of the design in these parts and the needs to strengthen or optimize the aforementioned parts of the moldboard plow chassis. [ABSTRACT FROM AUTHOR]

Pre-compression stress (σ pc ) has been widely used as a criterion for assessing the susceptibility of soil to compaction. Confined compression (CCT), semi-confined compression (SCCT) and plate sinkage (PST) tests are the most practical procedures to estimate σ pc . Discrepant estimates of σ pc may be obtained from the above tests mainly due to differences in boundary conditions. The aim of this study was to simulate these compaction tests using the finite element method (FEM) to compare σ pc estimated from stress-strain curves with the simulated yield stress. It was hypothesized that for a given simulated yield stress, σ pc estimated either at the point of maximum curvature or the point of Casagrande's method is not the same as simulated yield stress for different tests. FEM models were developed in ABAQUS with elastic-perfectly plastic law and Drucker-Prager yield criterion for the soil material. Yield stresses of 20, 50, 75, 100, 125, 150, 200 and 300 kPa were examined. The results showed that the stress at the point of maximum curvature was close to the simulated yield stress in CCT but smaller than that in SCCT and PST. Casagrande's method overestimated σ pc (averagely by 40%) for all the tests. A more precise estimate of σ pc was obtained at the point of maximum curvature than the Casagrande’s method in experimental CCT and PST on remolded soils. Cyclic loading-unloading CCT and PST to different stress levels showed that a safe threshold for preventing a severe plastic strain is significantly smaller (with a factor of 0.5 and 0.8 for CCT and PST, respectively) than σ pc in either of the tests. [ABSTRACT FROM AUTHOR]