The results of quasi-static four-point bend tests and of dynamic bend tests on freefree beams, both continuous and notched, are reported. Angles of bend and rotation are measured as a function of time after impact, where the angle of bend is defined as the angle of deflection o~ one part ot the beam relative to a neighbourlng segment ot the beam, and the angle of rotation is the angle of deflection relative to a datum line through the initial axis of the beam. The effect of notches is to change the strain profile in the beams, localize plastic deformation and provide sites for fracture initiation. The influence of the notch depends on its position and depth; however, the responses of beams in terms of angles of bend and rotation are similar for notched and unnotched cases and are also insensitive to notch depth, being governed primarily by inertia of the rotating sections rather than the strength of the joint. Elastic deformation and wave propagation are shown to be important. Comparisons of angles of bend and rotation as functions of time are made with a rigid-plastic solution and with two-dimensional finite-element computations, both of which slightly underestimate the angle of bend at any time after impact.
NOTATION
a0,a I acceleration of impact and free ends of beam respectively c notch depth divided by beam depth l length of beam m mass per unit length of beam Mo moment about plastic hinge in beam Mc moment about hinge in notched beam Mx moment at position x P applied load P' shear force transmitted across hinge V~ shear force at position x x, xh position along beam, hinge position eto,al angular acceleration of impact and free ends of beam respectively ~/ fractional reduction of M0 for notched beam dimensionless position of hinge in beam ix dimensionless load parameter