Name: how strain gauges measure deformation
Uploaded: 2024-05-23T12:59:55.000Z
Duration: 1 min 27 s
Channel: JoVE

Die Dehnung misst die Verformung oder Verschiebung in einem Material. Die Normaldehnung wird berechnet, indem die Längen vor und nach dem Aufbringen einer Last verglichen werden.
Eine genauere Methode zur Messung normaler Dehnungen ist die Verwendung von elektrischen Dehnungsmessstreifen, die aus einem dünnen Draht bestehen, der auf zwei Blätter Papier geklebt ist.
Wenn sich das Material dehnt, nimmt die Länge des Drahtes zu und sein Durchmesser ab, was zu einer Erhöhung des elektrischen Widerstands führt. Durch die Messung dieser Stromänderung wird die genaue Dehnung bestimmt.
Dehnungskomponenten an einem bestimmten Punkt können bestimmt werden, indem die Normaldehnung über die Achsen gemessen wird, die durch diesen Punkt gezogen werden. Eine dritte Messung entlang der Winkelhalbierenden des von den Achsen gebildeten Winkels bestimmt die Schubdehnung.
Die Dehnungsmessungen erfolgen entlang von drei Linien, die durch einen Punkt gezogen werden und mit der horizontalen Achse die entsprechenden Winkel bilden.
Die entsprechenden Dehnungsmessungen werden in die normale Dehnungsgleichung eingesetzt, um drei Dehnungsmessgleichungen zu bilden.
Die Anordnung von Dehnungsmessstreifen, die zur Messung von Dehnungen verwendet werden, wird als Dehnungsrosette bezeichnet, typischerweise in 45°- oder 60°-Konfigurationen.

dehnungsmessungen

Measurements of Strain

Die Dehnung quantifiziert die Verformung eines Materials unter Krafteinwirkung, typischerweise gemessen als normale Dehnung, die die Längenänderung im Vergleich zur ursprünglichen Länge darstellt. Zur Erhöhung der Genauigkeit werden elektrische Dehnungsmessstreifen verwendet. Diese Geräte bestehen aus einem leitenden Draht, der auf einer Papierunterlage montiert ist und an der Materialoberfläche haftet. Diese Messgeräte nutzen den piezoresistiven Effekt, bei dem sich der elektrische Widerstand des Drahtes als Reaktion auf mechanische Verformung ändert. Der Dehnungsmessstreifen passt sich an, wenn sich das Material ausdehnt oder komprimiert, und verändert den Widerstand des Drahtes proportional zur erfahrenen Dehnung.

Um die Spannung an einem bestimmten Materialpunkt umfassend zu verstehen, berücksichtigen Sie die Normal- und Scherspannungen, die für Formänderungen bei konstantem Volumen verantwortlich sind. Für diese Analyse sind mehrere Dehnungsmessstreifen erforderlich, die in verschiedenen Ausrichtungen angeordnet sind. Dehnungsmessungen werden typischerweise entlang von Linien durchgeführt, die in definierten Winkeln zu einer horizontalen Achse angeordnet sind, wobei diese Messwerte zur Berechnung der Gesamtdehnungskomponenten verwendet werden.

Eine Dehnungsmessstreifen-Rosette, die mehrere Messgeräte in Konfigurationen wie 0°, 45° und 90° oder 0°, 60° und 120° positioniert, ermöglicht gleichzeitige multidirektionale Dehnungsmessungen. Eine solche Anordnung ist für eine detaillierte Dehnungsanalyse an einem bestimmten Punkt von entscheidender Bedeutung und wird häufig in der Strukturanalyse, Materialprüfung und Teilevalidierung eingesetzt. Diese Methoden sind für Ingenieure von entscheidender Bedeutung, um das Materialverhalten zu bewerten und das Design und die Sicherheit technischer Strukturen zu verbessern.

Dehnungsmessungen

Die Dehnung misst die Verformung oder Verschiebung in einem Material. Die Normaldehnung wird berechnet, indem die Längen vor und nach dem Aufbringen einer Last verglichen werden.
Ein mehr ...

Education

Lehre

JoVE Core

Mechanical Engineering

Maschinenbau

Unit 1

Einheit 1

Transformations of Stress and Strain

Spannungs- und Dehnungstransformationen

KEY TERMS AND CONCEPTS

ZENTRALE BEGRIFFE UND KONZEPTE

how strain gauges measure deformation

Strain describes how a material deforms when a force is applied. Normal strain compares the change in length with the original length. Engineers use this measure to track stretching or compression in materials.

For higher accuracy, they often use electrical strain gauges. A strain gauge has a conductive wire on a paper backing that sticks to the surface of the material. It works through the piezoresistive effect, which means the wire’s electrical resistance changes when the material is bent, stretched, or compressed.

As the material elongates or shortens, the strain gauge changes with it. That change alters the wire’s resistance in proportion to the strain. To understand strain at one point more fully, engineers also consider normal strain and shearing strain, which describe shape change at constant volume.

This more detailed analysis needs several strain gauges placed at different angles. Strain is often measured along lines set at defined angles to a horizontal axis. The readings are then used to calculate the overall strain components.

A strain gauge rosette makes this process easier by arranging multiple gauges together. Common layouts include 0°, 45°, and 90°, or 0°, 60°, and 120°. These setups allow simultaneous measurements in multiple directions and are widely used in structural analysis, materials testing, and part validation. Engineers use the results to study material behavior and improve the design and safety of engineered structures.

How Strain Gauges Measure Deformation

transformation of plane stress

Plane Stress Changes with Rotation

Plane stress changes with rotation in a material element. The analysis looks at a prismatic element inside a cube under plane stress. As the element turns, the normal stress and shearing stress on its faces change in both size and direction. These changes are described with trigonometric functions of the rotation angle. The forces on the rotated faces are compared with the forces on the original faces that are perpendicular to each principal axis. The equilibrium equations use only the forces...

principal stresses

Stress Circle for Principal and Shear Stress

The stress circle shows how normal stress and shearing stress change with angle on a transformed plane. Its center, C, lies on the vertical axis and represents the average normal stress. The radius shows the amount of stress variation as the plane rotates. Points A and B, where the circle crosses the horizontal axis, mark the maximum and minimum normal stresses. At these points, shearing stress is zero. These points define the principal stress planes, where only normal stress, called principal...

principal stresses: problem solving

Finding Principal Planes and Stress Limits

Principal planes and principal stresses are found by analyzing two planes that meet at right angles under shearing, tensile, and compressive stresses. The goal is to use the given stress values to describe how the material is loaded and to locate the planes where the stress state changes. To find the principal planes, use the formula that relates the plane angle to twice the shearing stress divided by the difference between tensile and compressive stresses. After substituting the known stress...

mohr&#39;s circle for plane stress

Reading Stress Components with Mohr's Circle

Mohr's circle is a graphical way to read the stress state at a point in a material under plane stress. It turns normal stress and shearing stress into a two-dimensional picture. This makes stress transformation easier to analyze. The method uses Cartesian coordinates. The horizontal axis shows normal stress, written as σ, and the vertical axis shows shearing stress, written as τ. Two points, A and B, are plotted from the stresses on the element. Point A is at (σx, -τxy), and point B is at (σx,...

general state of stress

Stress Tensor and Principal Stresses

The stress tensor describes the internal forces inside a material. It is used when a material is under external force or deformation. At a point such as O, the tensor can show the stress components on any plane through that point. A tetrahedral element helps show how these forces act. One face, XYZ, is perpendicular to the line OA. The other faces line up with the coordinate axes, and point O is the origin. The stress on the tetrahedron is split into normal and shear components on each face. <br...

yield criteria for ductile materials under plane stress

yield-criteria-for-ductile-materials-under-plane-stress

Tresca and Von Mises Yield Criteria

Ductile materials can yield when they are loaded beyond a safe stress level. Engineers use yield criteria to check whether structural elements and machine parts can handle the expected load without permanent deformation. The yield point is first found with a tensile test, which measures how the material responds to uniaxial stress. A tensile test is not enough when a part faces biaxial or plane stress conditions. In those cases, more advanced criteria are needed to predict failure. One common...

transformation of plane strain

Plane Strain Under Rotated Axes

Plane strain changes when the coordinate axes are rotated. This matters for long bars and similar elongated structures that are loaded uniformly on their sides. In these members, one dimension is much larger than the others, so deformation is mainly studied in a single plane. At a point such as O, the key strain components lie along the x and y axes. The strain along the z-axis is negligible in plane strain. Together, the x and y strain components describe the deformation state in the xy-plane.

mohr&#39;s circle for plane strain

Principal and Shear Strains on Mohr’s Circle

Mohr’s circle for plane strain shows how normal strain and shear strain change on a graph. The horizontal axis is normal strain, written as ε, and the vertical axis is shear strain, written as γ. It uses two plotted points, X and Y, to represent the strain state. Point X has coordinates (εx, -γXY), and point Y has coordinates (εY, γXY). The center of the circle, O, gives the average normal strain. The radius comes from the relationship between normal strain and shear strain, so the circle...

three-dimensional analysis of strain

Principal Strain Directions in 3D

Three-dimensional strain analysis shows how a material changes shape when it is loaded. It is especially useful for elastic, homogeneous materials. A small cubic element inside the material can expand or contract along principal stress axes. That change turns the cube into a rectangular parallelepiped, which makes the deformation easier to picture. The principal stress axes are orthogonal, or at right angles to each other. Along these directions, the stress does not create shear inside the...

measurements of strain

Strain describes how a material deforms when a force is applied. Normal strain compares the change in length with the original length. Engineers use this measure to track stretching or compression in materials. For higher accuracy, they often use electrical strain gauges. A strain gauge has a conductive wire on a paper backing that sticks to the surface of the material. It works through the piezoresistive effect, which means the wire’s electrical resistance changes when the material is bent,...

key terms and concepts

Learn how strain gauges measure deformation, from normal and shearing strain to rosette layouts used in structural analysis and materials testing.

How Strain Gauges Measure Deformation | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

How Strain Gauges Measure Deformation

Description

Transcript

Tags