Library of Failures

Stress Corrosion Cracking of Aluminium Casting

AlSi7Mg0.55 die cast aluminium exposed to cyclical stresses in a sea water environment. Heat treatment history unknown. Examination of the fracture surface revealed fractographic ‘beach markings’ highlighting the origin of progressive crack growth. The microstructure consisted of alpha phase and silicon eutectic with isolated intermetallic phases consistent with the alloy grade. Intergranular cracking and corrosion attack was observed at the surface, consistent with Stress Corrosion Cracking (SCC) preferential to the alpha phase. SCC was a result of exposure to a chloride rich environment combined with service stresses. SCC then provided a stress raiser for fatigue crack initiation and propagation resulting in fracture.

Examination and Analysis of Powder Coat Interfacial Contamination

A manufacturer approached SureScreen Materials requesting support with identification of the source of contamination in their powder coating process. This was requested following identification of surface defects present on a powder coated component. The manufacturer provided the defective component for examination of the defects and examination and analysis of any associated contamination.

Gear Shifter Pawl Wear Investigation

Gear shifter pawls from different suppliers were found to exhibit different wear profiles.

Analysis of electronics housing deposit 

Electrical assemblies with a transparent polycarbonate cover were received for examination following the observation of contamination on the internal surfaces. 

Stress Corrosion Cracking of 304 Grade Stainless Steel

Multi-branched, transgranular cracks characteristic of stress corrosion cracking (SCC)

Bearing Rolling Contact Fatigue

A rolling element bearing exhibiting rolling contact fatigue (RCF) spalling of the working surfaces.

Ball Plate Cracking

Cracked, martensitic (hardened) grey cast iron ‘ball plate’ used to shape ball bearings.

316L Process Pipe Corrosion

Three weeks after installation, 316L pipework started to leak from pinhole defects. These were predominantly located at welds that exhibited high temperature oxidation (heat tints) at the heat affected zones. Those welds that did not exhibit such oxidation were unaffected.

Overheated Bearing Shells

The white-metal-coated steel bearing shells on a crankshaft had failed during testing. Examination revealed that the core of the bearing had a ferrite and pearlite microstructure, but in some areas the working surface has been transformed to bainite.

Overload Cracking of Gear

The gear flanks exhibited large amounts of deformation and wear consistent with high loads during service. Cross-sectional examination of the teeth showed multiple brittle or staged cracks to have propagated from the flank surface though the edge of the case, with dominant cracks opening up in the latter stages of the failure.

Quench Cracking of Forging

A forging was found to be cracked at inspection by using magnetic particle inspection.

Reverse Engineering of 1960s Locomotive Component

A bell housing used on a 1960’s locomotive required remanufacturing and the original component, that was beyond economical repair.

Staged Overload of Threaded Component

Visual examination of the fracture revealed the initiation portion to be at nominally 45°, which is typical of shear.

Torsional Overload of Crankshaft Spline

The fracture surface was relatively flat and displayed radial arced markings on the majority of the fracture surface.

Torsional Overload of Threaded Shaft

A threaded shaft had fractured at an end face of a nut. The shaft had failed by torsional overload and evidence of twisting of the bolt section was observed on microexamination of cross-sections.

Fracture of Aluminium Component Due to a Casting Defect

Examination of the fracture at low magnification revealed a change in fracture surface colour and form for approximately two thirds of the surface area.

Degradation of Kolsterising Coating and associated damage

Examination revealed that the surfaces of the seized eye and boss had degraded by a fretting mechanism with the resulting deposits having caused seizure of the joint.

Casting Defect in Cast Steel flange

The crack propagation was consistent with the opening (and joining up) of pre-existing interdendritic shrinkage cracks.

Casting Defect in Copper Alloy

Tapping Tee joints used in water pipe applications had been found to leak from a pin hole defect after installation in service.

Stress Corrosion Cracking of a Copper Alloy Component

A copper alloy component had cracked in service and the cracks exhibited a degree of ‘yawning’ (opening) indicative of the presence of tensile stress.

Torsional Overload of Lifting Chain

Fractured chain used in service to lift a skip used inside a grit-blasting chamber. The chain consisted of 10mm links with a C-hook, an ‘egg link’, and an eye.