Device and method for measuring sectional forces

A method for measuring sectional forces on a single-piece structural element in respect of a sectional plane by a plurality of strain gauges,

• wherein the structural element comprises a first and a second outer wall, which extend perpendicular to the sectional plane, extend in a mirror-symmetrical manner in relation to each other about a first mirror plane of symmetry and are connected by further outer walls, wherein the first mirror plane of symmetry extends perpendicular to the sectional plane,
• wherein each strain gauge has a measurement direction, and the electrical resistance of the strain gauge depends on the length of the strain gauge in the measurement direction, and
• wherein the method comprises:
• providing a cavity in the structural element,
• introducing into the first outer wall, in the region of the cavity, at least three openings, which are separated from each other by webs connect the cavity to the exterior of the structural element, wherein the webs extend away from a common point,
• introducing into the second outer wall, in the region of the cavity, at least three openings, which are separated from each other by webs extending away from a common point and connect the cavity to the exterior of the structural element, wherein the openings and webs of the second outer wall are arranged in a mirror-symmetrical manner about the first mirror plane of symmetry in relation to the openings and webs of the first outer wall,
• arranging a first and a second strain gauge of the plurality of strain gauges on the webs of the first outer wall, and arranging a third and a fourth strain gauge of the plurality of strain gauges on the webs of the second outer wall, wherein the strain gauges are arranged such that, when the structural element is loaded with a first force acting parallel to the sectional plane and parallel to the first mirror plane of symmetry, the first and third strain gauges undergo an identically oriented change in length in the measurement direction, the second and fourth strain gauges undergo an identically oriented change in length in the measurement direction, and the change in length of the first and third strain gauges is opposite to the change in length of the second and fourth strain gauges,
• interconnecting the first to fourth strain gauges to form a Wheatstone bridge, wherein the first and second strain gauges are connected in series and parallel to the fourth and third strain gauges, which are likewise connected in series, wherein a voltmeter measures the voltage drop between a node between the first and second strain gauges and a node between the fourth and third strain gauges,
• applying a supply voltage, which drops across the first and second strain gauges, and also across the fourth and third strain gauges,
• applying the first force to the structural element, and
• determining the voltage drop on the voltmeter upon action of the first force.