Patent ID: 8950268
Filing Date: 2015-02-10
Classification: G01N

Abstract:
1. A material testing machine measuring strain of a tube-like test piece by applying inner pressure and stress in a tube axis direction to the test piece, comprising: a plurality of radial direction displacement detection units that detect displacements of an outer circumferential surface of the test piece in a radial direction in a central portion of an effective length of the test piece; an axis direction displacement detection unit that detects a displacement in the tube-axis direction of the outer circumferential surface of the test piece in the central portion of the effective length of the test piece; and a calculation unit that calculates the strain in a circumferential direction and the tube-axis direction of the test piece in the central portion of the effective length, based on detection results by the plurality of radial direction displacement detection units and the axis direction displacement detection unit, wherein: the plurality of radial direction displacement detection units respectively detect displacements at different directions around the tube axis of the test piece; each of plurality of radial direction displacement detection units comprises a first displacement meter that detects a displacement in the radial direction of the outer circumferential surface of the test piece in the central portion of the effective length; at least one of the plurality of radial direction displacement detection units comprises a second displacement meter that is aligned with the first displacement meter in the tube axis direction and detects a displacement in the radial direction of the outer circumferential surface of the test piece; and each of the first and second displacement meters comprises: wherein: a tip of the contact of the displacement sensor is arranged to contact a stopper plate provided on the fixed frame; the needle is arranged such that a lengthwise direction is oriented in the radial direction of the test piece; the needle is attached to the movable frame such that the needle protrudes from an end of the movable frame facing the test piece; the displacement in the radial direction of the circumferential surface of the test piece is detected by detecting a moving amount of the needle; and the calculation unit calculates a curvature radius in the tube axis direction of the outer circumferential surface of the test piece in the central portion of the effective length, based on detection results by the first and second displacement meters of the at least one of the plurality of radial direction displacement detection units.