INVESTIGATION OF REPEATED FAILURE OF MOVABLE JOINTS IN HEAVY VEHICLES

Abstract

Combat armored vehicles contribute significantly in military forces, they performed general or specified mission and support all war fighting function.WMZ551B is armored personnel carrier. The movable joint in a steering system is one of the main parts used to attain stability and steady movement of the vehicle. A repeated failure is detected in the steering mechanism at the movable joint of armored vehicle. The transmission system of the vehicle consists of several components which sometimes encounter unfortunate failures. Some of this failure may cause by the manufacturing and design faults, material faults, maintenance faults as well as user originated faults. The work in this research is carried out to investigate the failure mechanism and cause of the failed part of the movable joint. The work dealt with two steps. First part involves the experimental process, including the metallurgical analysis and mechanical testing to find out the properties of the material and identify the fracture mechanism. While second part involves stress analytical analysis to determine the combined stresses affecting the failure part. The chemical tests for the steering movable joint shows that the joint part has low carbon content of (0.208%) and higher content of chromium (0.873%) results in adherent, stable chromium oxide for corrosion resisting property of the material. Rockwell hardness test is conducted at the specimen and the results shows that the specimen has a surface hardening with 60 HRC at the outside surface and around 16 HRC at the cross section area. Examination of the fractured surface with SEM machine revealed a combination of ductile and brittle overload (dimpled rupture and cleavage) fracture with no indications of progressive crack growth via fatigue noticed. This transition in fracture morphology coincided with the change in properties of the material.