January_February_2022_AMP_Digital

1 8 A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y / F E B R U A R Y 2 0 2 2 for analysis was the remnant fillet weld fracture. The questions to be answered were: did the weld contain weld de- fects? Was this a single pass weld or multipass weld? Did the weld exhib- it adequate penetration into the base steel? Did the weld fail due to impact, fatigue, or improper welding practice/ procedures? Due to the saddle size and weight, the fillet weld area was water jet cut into smaller sections for handling and examination. Figure 3 shows a CT slice of a sec- tion of the weld remnant area select- ed for analysis. The CT revealed large slag inclusions, porosity, and lack of weld material in some locations. The size, location, and number of voids can be quantitated using CT software anal- ysis. Two metallographic planes for cross-sectional metallographic analysis were selected based on the locations in the CT scan showing weld defects. Figure 4a shows a CT slice location of the fillet weld fracture in profile. Note the details of the weld only show (a) (b) metallography and materialography techniques require the use of a micro- scope to examine features including grain size, grain orientation, phase iden- tification, phase interfaces, cracks, and porosity typically found at the micron length scale. Specimen preparation re- cipe improvements, automation, and guides to specimen preparation are con- tinually being researched, updated, and studied by universities and suppliers. Because it is considered a destruc- tive testing technique, materialography from a forensic engineering perspec- tive normally encounters resistance from parties involved in litigated mat- ters as it could be considered spolia- tion of evidence if the parties are not in agreement with protocols for materia- lographic evaluation. This hurdle can be overcome by identifying the evidentia- ry value of performing metallography/ materialography and ex- plaining the reasons to the trier(s) of fact. CASE STUDY 1: EXAMINATION OF A FRACTURED STRUCTURAL FILLET WELD The remnants of a fractured structural weld were provided for a fo- rensic metallurgical ex- amination. The analysis consisted of digital pho- tography, high-resolution µCT scan of the weld loca- tions, fractography of the fracture surface, and me- tallography to characterize the weld microstructure. Figure 1 shows an image of a saddle and post contain- ing a structural fillet weld. Figure 2 shows an im- age of a fractured structur- al weld, the remnants of which remain on the sad- dle. The area of interest Fig. 1 — An intact fillet weld on a structural saddle and post. Fig. 2 — Fracture remnants of a fillet weld remaining on saddle. The red box indicates the area selected for analysis. Fig. 3 — CT slice image of top left quadrant shows porosity, lack of weld material in weld remnant. Lines indicate locations selected for cross-sectional planar analysis. Fig. 4 — (a) CT slice as indicated by the red line in Fig. 3 shows planar section of weld. Note internal porosity detail. (b) Metallographic cross section of weld fracture in etched condition shows porosity, slag inclusions, and multiple HAZ in base steel.