Strain testing rig and method of evaluating strain characteristics of specimen

A strain testing rig for testing an elongate specimen having a first end portion and a second end portion spaced apart along a specimen axis and a length extending from the first end portion to the second end portion along the specimen axis, the strain testing rig comprising:

• a first grip for gripping the first end portion of the specimen;
• a second grip for gripping the second end portion of the specimen;
• wherein each of the first grip and the second grip comprises a tapered dog having angled sections shaped and arranged to engage tapered shoulders of the specimen facing inboard along the specimen axis such that the tapered dog is configured to press outboard against the tapered shoulders as the drive mechanism moves the first grip away from the second grip to stretch the specimen lengthwise, each dog having an inboard end portion and an outboard end portion spaced apart along a longitudinal X axis, each dog being configured so that the X axis is parallel to the specimen axis at the respective end portion of the specimen, each dog also having a Y axis perpendicular to the X axis, and a Z axis perpendicular to the Y axis and the X axis, the dog defining a cavity configured to receive the respective end portion of the specimen therein, each cavity having an inner dimension parallel the Z axis of the dog and including a tapered section along which the inner dimension decreases as the cavity extends inboard along the X axis, each dog comprising a base extending generally in an X-Z plane and first and second side walls extending along the Y axis from the base, the first and second side walls being spaced apart along the Z axis, each grip further comprising a clamp for clamping the first end portion of the specimen along the X axis against the angled sections of the first and second side walls, wherein each grip comprises an outboard end wall and wherein each clamp comprises a set screw threadably connected to the respective outboard end wall, and
• a drive mechanism configured to move the first grip away from the second grip to stretch the specimen lengthwise;
• wherein the first grip and the second grip are configured to maintain a grip on the specimen as cross-sectional area of the specimen decreases during stretching.

A strain testing rig for testing an elongate specimen having a first end portion and a second end portion spaced apart along a specimen axis and a length extending from the first end portion to the second end portion along the specimen axis, the strain testing rig comprising:

• a first support including a first brace plate;
• a second support including a second brace plate;
• a first grip mounted on the first support for gripping the first end portion of the specimen, the first grip comprising a dog having an inboard end portion and an outboard end portion spaced apart along a longitudinal X axis, the dog being configured so that the X axis is parallel to a longitudinal axis of the specimen, the dog comprising a base extending generally parallel to the X axis, and first and second side walls extending generally perpendicular to the base, wherein the first brace plate of the first support and the base of the dog of the first grip are positioned to engage opposite sides of the specimen;
• a second grip mounted on the second support for gripping the second end portion of the specimen;
• and
• a drive mechanism configured to move the first grip away from the second grip to stretch the specimen lengthwise;
• wherein each of the first grip and the second grip comprises a press for compressing the respective end portion of the specimen, each press comprising a linear actuator and a press plate, the linear actuator being configured to drive the press plate to compress the respective end portion of the specimen.

A strain testing rig for testing an elongate specimen having a first end portion and a second end portion spaced apart along a specimen axis and a length extending from the first end portion to the second end portion along the specimen axis, the strain testing rig comprising:

• a first grip for gripping the first end portion of the specimen;
• a second grip for gripping the second end portion of the specimen;
• and
• a drive mechanism configured to move the first grip away from the second grip to stretch the specimen lengthwise;
• wherein each of the first grip and the second grip comprises a clamp for clamping the respective end portion of the specimen along an X axis parallel to the specimen axis and a press for compressing the respective end portion of the specimen along a Y axis perpendicular to the X axis, the press comprising a linear actuator, a press plate and a linkage operatively connecting the linear actuator to the press plate, the linkage comprising a link pivotably connected to the linear actuator and the press plate being pivotably connected to the link.