*4.2.3 Chemical composition*

It is essential to check the chemical composition of any failed cast component to approve that it was manufactured from the standard material. A sample was extracted from the neck region of the rotor and investigated for its elemental composition. The measured value was verified against the standard material composition. The results are presented in **Table 1**. The chemical analysis of the failed rotor confirmed that the disc was produced from the appropriate GCI material and that there were no deficiencies or abnormalities in the composition.

*Failure Analysis – Structural Health Monitoring of Structure and Infrastructure Components*


#### **Table 1.**

*Elemental composition of the fractured brake disc (wt.%).*

#### *4.2.4 Microstructure analysis*

The microstructure of a material depends on its elemental composition and the processing technique used. Even at the same nominal constituents, the effect of the processing method can produce several other microstructural features in different metallic materials. Light optical and scanning electron microscopes were used to examine the brake rotor samples for their microstructure constituents. **Figure 6a** displays the LOM micrograph of the etched sample, and the SEM micrograph of the disc is presented in **Figure 6b**. The microstructure, shown in **Figure 6a**, displays no traces of free cementite, but 0.15% free ferrite (by phase volume fraction) was observed. It is also evident in **Figure 6** that the GCI disc contains graphite flakes, which conforms with the requirements according to the European Standard (EN ISO 945–1:2008) for GCIs rotor [28]. Based on this standard, the rotor microstructure should primarily consist of pearlite in its matrix and a maximum of 5% and 2% free ferrite and free cementite, respectively, by phase volume fractions. Also, the graphite morphology should be mainly Type-A with flakes size 3–4 according to the SS-EN ISO 945–1:2008 standard (**Figure 6b**). It is apparent in **Figure 6** that the matrix is principally pearlite

**Figure 6.** *Light optical (a) and SEM (b) micrographs of the rotor.*

## *Root Cause Failure Analysis of Castings: A Case Study of a Brake Rotor DOI: http://dx.doi.org/10.5772/intechopen.107950*

with a few manganese sulphide (MnS) particles and traces of steadite. It can be concluded from this study that there were no inconsistencies in the microstructure constituent of the failed disc, and therefore conforms with the microstructural specification for the disc material.
