Charles C. Roberts, Jr., Ph.D., P.E.

Metallic fasteners secure, attach, or connect, a myriad of mechanical components. One very common and highly successful fastener is the seemingly ordinary nut and bolt. Despite its wide use and acceptance, a small percentage of bolted connections fail for a variety of reasons resulting in property loss, personal injury or both. For instance, in Figure 1, an automobile control arm bolt failed as a result of defective heat treating, causing loss of control of the vehicle, property damage and personal injury.

Figure 1

Figure 2

In Figure 2, a snowmobile steering ski bracket failed, causing severe injury to the driver. The bolt had failed because of improper bolt application.

Figure 3

In Figure 3, insufficient torque had been applied to an automotive wheel stud, resulting in fretting of the wheel bolt hole area (black deposit on the chrome wheel surface), failure of the wheel studs, detachment of the wheel and an accident. An important ingredient in the assessment of subrogation potential from a bolt related accident is the recovery and preservation of the failed bolt. In instances where the bolt fractured into two pieces, recovery of both would be ideal, but one piece will show the fracture surface which is the mirror image of the other. Figure 4 is a typical bolt fracture surface showing a fracture origin area (red arrow), ratchet mark (green arrow) indicating relatively high stress or stress concentration and progression marks (blue arrow) showing direction of crack advancement. These features are utilized by the analyst to opine as to the probable cause of the failure and should be preserved.

Figure 4

If subrogation is contemplated, then anticipating the action of the respondent can help in planning an investigation. The typical defense of choice is spoliation and a Daubert hearing long before the merits of the case are discussed. Avoid the spoliation argument with proper storage of the bolts and nuts. Each of the individual failed bolt parts should be stored in separate packages to avoid damage to fracture surfaces. Minimization of corrosion or deterioration of the metallic surfaces during storage is recommended. Get an agreement between parties as to a protocol for nondestructive and destructive testing. Most microscopic analysis is nondestructive but hardness testing, tensile testing and chemical analysis are destructive. Avoid a Daubert hearing by making sure that the failure analysis is performed in a scientifically recognized manner with qualified analysts. Finally, the merits of a bolt failure case may take several forms based on the failure analysis and factual data. The bolt could be defectively manufactured, defectively designed, improperly installed, improperly torqued, or improperly selected for a particular application.