Name: how temperature changes create stress
Uploaded: 2023-04-30T12:29:32.000Z
Duration: 1 min 9 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.13

CHEM.13.D

Thermal Stress

Stress erfährt ein Körper, wenn er Temperaturschwankungen ausgesetzt ist, die als thermischer Stress bezeichnet werden und den Körper sogar dauerhaft verformen können.
Zum Beispiel wird absichtlich ein Raum zwischen zwei Gelenken einer Stange auf dem Gleis gehalten, um die Verformung oder Biegung von Stangen zu verhindern.
Um die thermische Spannung in einem Objekt zu berechnen, bestimmen Sie zuerst die thermische Ausdehnung oder Kontraktion und berechnen Sie dann die Spannung.
Betrachten Sie einen Stab der Länge L0.. Wenn Wärme angewendet wird, dehnt sich die Länge des Stabes um das Delta 'L' aus, und die prozentuale Änderung der Länge des Stabes kann ausgewertet werden.
Nun wird an beiden Enden die gleiche Stange befestigt. Wenn die Hitze angewendet wird, erfährt der Stab eine Spannung, da er sich nicht ausdehnen kann. Um die ursprüngliche Länge des Stabes wiederherzustellen, kann die Spannung berechnet werden.
In Anlehnung an die Definition des Elastizitätsmoduls handelt es sich um das Verhältnis von Spannung zu Dehnung.
Daher kann die thermische Spannung bestimmt werden, indem die Gleichungen kombiniert und die Terme neu angeordnet werden.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a>; S. 18–19.</li>
</ol>

thermische belastung

Wenn sich die Temperatur eines Objekts ändert und es daran gehindert wird, sich auszudehnen oder zu schrumpfen, ist das Objekt Belastungen ausgesetzt. Die Belastung ist komprimierend, wenn das Objekt sich ohne Einschränkung ausdehnt und dehnend, wenn es sich zusammenzieht. Diese Belastung, die durch Temperaturveränderungen entsteht, wird als thermische Belastung bezeichnet. Sie kann recht groß sein und Schäden verursachen. Um diese Belastung zu vermeiden, können Ingenieure Komponenten so entwerfen, dass sie sich frei ausdehnen und zusammenziehen können. Zum Beispiel werden auf Autobahnen bewusst Lücken zwischen den Blöcken gelassen, um zu verhindern, dass thermische Spannungen entstehen. Wenn keine Lücken gelassen werden können, müssen Ingenieure thermische Spannungen in ihre Designs einbeziehen. Deshalb bestehen die Bewehrungsstäbe in Beton aus Stahl, da der Linearausdehnungskoeffizient von Stahl nahezu dem von Beton entspricht.

Thermische Belastung kann viele Phänomene erklären, wie zum Beispiel das Verwittern von Felsen und Straßenbelägen durch die Ausdehnung von Eis beim Gefrieren. Eisenbahnschienen und Straßenbeläge können an heißen Tagen aufwölben, wenn ihnen ausreichende Dehnungsfugen fehlen, und Stromleitungen hängen im Sommer stärker durch als im Winter und können bei kaltem Wetter reißen, wenn der Spielraum nicht ausreichend ist. Risse öffnen und schließen sich in Gipswänden, wenn sich ein Haus erwärmt und abkühlt. Glasbackformen können reißen, wenn sie schnell oder ungleichmäßig abkühlen, aufgrund von unterschiedlicher Kontraktion und den resultierenden Spannungen.

Thermische Belastung

Wird die Temperatur eines Objekts verändert, während es daran gehindert wird, sich auszudehnen oder zusammenzuziehen, wird das Objekt belastet. Der Stress ist ...

Education

Lehre

JoVE Core

Physics

Physik

Unit 1

Einheit 1

Temperature and Heat

Temperatur und Wärme

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

how temperature changes create stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile.

This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up.

When gaps are not possible, thermal stress must be part of the design. In concrete, the reinforcing rods are made of steel because steel and concrete have nearly the same coefficient of linear expansion. That similarity helps the materials change length at nearly the same rate.

Thermal stress also explains many everyday and natural effects. Ice can weather rocks and pavements as it freezes and expands. Railroad tracks and roadways may buckle on hot days if they do not have enough expansion joints, and power lines can sag more in summer and snap in cold weather if they lack slack.

The same idea helps explain cracks that open and close in plaster walls as a house warms and cools. Glass cooking pans can crack if they cool too fast or unevenly. In each case, different contraction or expansion creates stress in the material.

How Temperature Changes Create Stress

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thermal stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile. This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up. When gaps...

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key terms and concepts

Learn how heating and cooling create compressive or tensile stress, why expansion joints matter, and how thermal stress affects roads, wires, walls, and glass.

How Temperature Changes Create Stress | JoVE K12

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CHEM.13.C

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How Temperature Changes Create Stress

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