Experimental investigation of the mechanical properties of used-bolts reused in Nigeria

In this research, the mechanical properties of used-bolts, reused in Nigeria were investigated using Monsanto Tensometer and visual hardness testing machine to ascertain their reliability in service, during the second usage as popularly heralded by most of the dealers and highly recommended by the technicians. The key parameters tested were the yield strength, ultimate tensile strength and the Brinnell Hardness Number (BHN). Ten samples each of the three used-bolt size categories (M8, M10, and M12) were tested for three key mechanical properties in accordance with the standard code (BS EN ISO 898-1) for mechanical properties of fasteners produced from carbon and alloy steel, under ambient temperature of 29.8°C. The results showed that, the yield strength, ultimate tensile strength and the BHN of these used-bolts not only fail to confirm with the standard code (BS EN ISO 898-1), but also vary randomly. Statistical analysis revealed significant high variations of these properties in the respective categories. These declared their unreliability. Hence Used-Bolts are not suitable for engineering applications due to these deviation from standards, and wide and random variation in their mechanical properties.