Abstract: A device to determine the operable failure mode of mechanically fastened lightweight composite joints by measuring the hole elongation of a bolted joint is disclosed. The double-lap joint test apparatus 10 comprises a stud 20, a test specimen 30 having a hole, two load transfer plates 31, and linear displacement measuring instruments 27. The test specimen 30 having a hole is sandwiched between two load transfer plates 31 and clamped together with the stud 20. Spacer washers 22 are placed between the test specimen 30 and each load transfer plate 31 to provide a known, controllable area for the determination of clamping forces around the hole of the test specimen 30 attributable to bolt torque. The spacer washers 22 also provide a gap for the mounting of reference angles 23 on each side of the test specimen 30. Under tensile loading, elongation of the hole of test specimen 30 causes the stud 20 to move away from the reference angles 23.