A bolt having a shank and integral head has a strip of photoelastic material mounted in the head for manifesting in the form of photoelastic... Show moreA bolt having a shank and integral head has a strip of photoelastic material mounted in the head for manifesting in the form of photoelastic fringes linearly related to bolt tension the bending stresses created in the head during loading of the bolt. To determine the tension in the bolt during or after loading, polarized light is directed toward the photoelastic strip and reflected light from the strip is analyzed to measure fringe order. The fringe order is related to the amount of bending stresses in the head of the bolt by a predetermined calibration curve, the bending stresses being linearly related to bolt tension. Sponsorship: IIT Research Institute United States Patent Show less
Fasteners such as mine bolts are provided with tension indicators to directly read tension in the shank of the bolt. The preferred tension... Show moreFasteners such as mine bolts are provided with tension indicators to directly read tension in the shank of the bolt. The preferred tension indicators comprise an elongated pin disposed in a bore formed in the bolt and connected at the bottom of the bore to the bolt shank to be tensioned thereby. The tension indicator further comprises a cross bar attached to the other end of the pin and extending laterally into engagement with another portion of the bolt, such as the head of the bolt, to be bent upon tensioning of the pin. Preferably, a photoelastic member is attached to the cross bar and bending stresses in the cross bar are manifested in the photoelastic member in the form of photoelastic fringes for reading by a reflection polariscope. Sponsorship: IIT Research Institute United States Patent Show less
