Test apparatus for providing axial stresses in a structure

A test apparatus for providing axial stresses in a structure, the structure having a first surface on one side and a second surface on an opposite side, wherein the test apparatus comprises:

• a first set of formations for abutting the first surface of the structure at a first plurality of locations on the structure,
• a second set of formations for abutting the second surface of the structure at a second plurality of locations on the structure, the first and second plurality of locations defining different footprints, and
• a force actuator for applying a force which urges at least one of the first and second set of formations towards the other set, and
• wherein each set of formations comprises at least three formations and wherein at least two formations in each set of formations are aligned with a notional alignment line along the structure and at least one formation in each set of formations is out of alignment along the structure with said notional alignment line,
• such that when the force actuator applies the force which urges at least one of the first and second set of formations towards the other set, loads are applied at different locations over each notional alignment line and at a further location out of alignment with each notional alignment line, causing the structure to bend biaxially and thereby providing biaxial stresses in the structure, wherein each set of formations comprises four formations and wherein the four formations comprise a first pair of formations aligned along a first notional alignment line and a second pair of formations aligned along a second notional alignment line, and wherein the first and second alignment lines are at an angle to each other, and wherein each formation is arranged to provide a line of contact with the structure and wherein the line of contact of each formation is approximately perpendicular to its notional alignment line.