Vpliv prednapetja na dinamično nosilnost vzvojne vzmeti : doktorska disertacija

slovenian

doktorska dela

2009

Univerza v Mariboru, Fakulteta za strojništvo

Doctoral dissertation discusses life cycle depending on pre-stress and breaking behavior character of torsion bar springs and torsion hollow springs. Torsion springs are used for wheel suspension in the mobile technology. Torsion bar springs are dynamically loaded and can be broken due to fatigue. The quality of these springs is seen on the achieved life cycle and the expanse of torsion stress that loads the spring during its usage. Torsion bar springs are highly sensitive to surface irregularities which can be reduced by surface cold rolling while a higher working angle of the springs is achieved through the pre-stress in the plastic area. Torsion bar spring's life depends on the pre-stress level and the size of dynamic loading. There is a calculating model for prediction of a life cycle of torsion bar springs depending on the level of pre-stress and the height of dynamic loading for intentionally produced spring steel. Two characteristic cracks were determined; transversal crack that results as a crack initiation inside material; while spiral spring crack results as a surface irregularity. The enlargement of torsion hollow spring's life is achieved by compress pre-stress in axial direction. Compress pre-stress and working torsion loading create biaxial stress state that enlarges the number of cycles and hereby extends the time to initiation of fatigue crack. Compress pre-stress has a favorable impact on the breaking character of the torsion hollow springs, since it reduces the influence of the surface quality on the life cycle. Compress stress decelerates initiation on the surface of hollow torsion springs, the crack is spread under the impact of plane stress state. With alternating loaded pre-stressed torsion hollow springs the crack is spread in the form of two spirals on the circumference of the hollow springs. In the doctoral dissertation an approach is analyzed that enables enhanced life of the torsion hollow springs through axial pre-stressing so it can be expanded on other torsion bending loaded machine elements

08.08.2023