Yasuki Kita

Development of the Strength Evaluation Method for Body of Mining Dump Truck Under Actual Operations

The prediction method of the experimental stress wave at the welded joints of the body under actual operations was developed, and the strength evaluation flow based on the method was proposed.We conducted running tests using a dump truck prototype, the EH3500ACII, as an experimental approach. The high accelerations in longitudinal, vertical, and lateral directions were measured for a sudden stop, bump override and sharp turn test, respectively. The tendencies of the stress waveforms at the welded joints in each running test are in good agreement with those of the acceleration waveforms.The distinct element (DE) and finite element (FE) methods were used to predict the experimental stress waves. First, the pressure loads of soil were analyzed using DE method. Kanto loam (Japanese soil) was modeled using a large number of particles, and filled a container modeled using rigid plates to form a shape similar to that of actual loads. The soil pressure distributions were formulated with a variety of acceleration loads. Next, the obtained load pressures were applied to the FE model as the load conditions. The stresses at the evaluation points were calculated under a 1G acceleration in the vertical, lateral, and longitudinal directions, respectively. Finally, those stress results and the measured time series acceleration data were multiplied, and the stress waveforms under running conditions were predicted by using a linear superposition method.When the analytical stresses were compared with the experimental results, the tendencies of the analytical stress variations corresponded well with those of the experimental stress waveforms. On the other hand, the analytical stresses were smaller than the actual experimental values. This was because the weld geometries were not modeled in FE model, and the stress concentrations on the weld toes were not precisely estimated.The strength evaluation flow was developed by using the soil pressure distribution formulated using the DE analysis, the database of the time series acceleration data obtained from the running tests, the ratio of the stress ranges of the experiment and that of the analysis, Kstress_ratio, and the strength criteria for welded joints. It is possible to evaluate the durability of a new structure model in a short period of time by using this evaluation flow.Copyright

Crack-Tip Shielding Effect on Fatigue Crack Propagation in Porous Silicon Carbide

A sharply notched specimen of porous silicon carbide with porosity of 37% was fatigued under four-point bending. The opening displacement of a fatigue crack was measured at several positions along cracks by using scanning electron microscopy. The crack propagation curve was divided into stages I, II, and III. The crack propagation rate first decreased with crack extension in stage I and became constant in stage II. In stage III, the crack propagation rate increased again. The range of crack opening displacement measured in SEM was lower than that calculated from the applied load range by FEM, suggesting that the anomalous variation of the crack propagation rate with crack extension was caused by crack-tip shielding due to crack face contact. The crack-tip stress intensity factor was estimated as a true crack driving force from the relation between the crack opening displacement and the applied load. The amount of crack-tip shielding increased very quickly with crack extension, reducing the crack-tip stress intensity factor in stage I. In stage II, the increasing applied stress intensity factor is balanced by the increase in the crack-tip shielding. The crack-tip stress intensity factor increases with crack extension in stage III.