Name: stress components on a loaded body
Uploaded: 2024-03-07T13:22:33.000Z
Duration: 1 min 15 s
Channel: JoVE

Considérons un corps soumis à de multiples charges. Lorsqu’on dissèque un point à l’aide d’un plan parallèle au plan xy, on observe que les forces de cisaillement agissent sur une petite zone entourant le point.
Considérons une partie du corps soumise aux charges précédemment indiquées, la force normale agissant le long de l’axe z
Les forces de cisaillement n’ont pas de direction bien définie sur un plan de section, elles sont donc résolues en deux forces composantes parallèles aux axes x et y.
L’amplitude de chaque force est ensuite divisée par l’aire pour obtenir les composantes de contrainte.
Le premier indice des contraintes indique qu’elles s’exercent sur la surface perpendiculaire à l’axe z. Le deuxième indice des contraintes de cisaillement identifie la direction.
Lorsque l’autre côté du plan vertical est analysé, il produit les mêmes composantes de contrainte mais dans des directions opposées.
En faisant passer des sections par le point parallèlement aux plans yz et zx, des composants de contrainte supplémentaires peuvent être définis.

contrainte : conditions générales de chargement

Stress: General Loading Conditions

Pour saisir la complexité des conditions réelles dans lesquelles plusieurs charges sont appliquées simultanément à une structure, on peut visualiser une section passant par un point spécifique d'un corps, alignée parallèlement au plan xy. Cette section est soumise à diverses forces, notamment les charges d'origine, les forces normales et les forces de cisaillement.

La force de cisaillement, possédant une direction potentielle dans le plan de la section, est simplifiée en deux forces composantes parallèles aux axes x et y. Chaque force est divisée par la surface et, à mesure qu'elle s'approche de zéro, trois composantes de contrainte distinctes (σ_z, τ_zx et τ_zy) sont définies. L'indice initial de ces composants indique que les contraintes sont exercées sur une surface perpendiculaire à l'axe z, tandis que le deuxième indice identifie la direction du composant.

Les signes de ces composantes indiquent une tension (positive) ou une compression (négative). Une analyse similaire sur la partie droite du corps aboutit à des composantes de contrainte identiques mais dans des directions opposées. Des composantes de contrainte supplémentaires peuvent être déterminées en faisant passer des sections à travers le point parallèlement aux plans yz et zx. Cette analyse aide à démêler l’interaction complexe des forces et des contraintes dans des conditions de chargement complexes.

Contrainte : Conditions générales de chargement

Considérons un corps soumis à de multiples charges. Lorsqu’on le dissèque en un point à l’aide d’un plan parallèle au plan xy, on observe que le cisaillement ...

Education

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JoVE Core

Mechanical Engineering

Génie mécanique

Unit 1

Unité 1

Concept of Stress

Le concept de stress

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

stress components on a loaded body

Stress components on a loaded body can be found by cutting the body through a point with a plane parallel to the xy plane. That section carries the original loads, along with normal forces and shearing forces. The result is a simple way to describe how a structure responds under combined loading.

The shearing force in the section can point in different directions within the plane. It is split into two parts that run parallel to the x and y axes. Each part is divided by the area, and as that area becomes very small, three stress components are defined: σz, τzx, and τzy.

The first subscript in each symbol shows the surface orientation. It means the stress acts on a surface perpendicular to the z-axis. The second subscript shows the direction of the stress component. The sign of each stress component shows whether the material is in tension, which is positive, or compression, which is negative.

If the body is viewed on the right side of the cut, the same stress components appear in opposite directions. Similar stress components can also be found by making sections parallel to the yz and zx planes. This method helps describe the full set of stresses that can act at a point when several loads act at once.

Stress Components on a Loaded Body

normal stress

Normal Stress in Axial Loading

Normal stress acts perpendicular to a material’s cross-sectional area. It appears when a force is applied along the axis of an object, which is called axial loading. Bridge truss members are a practical example of this kind of loading. When a rod carries axial load, internal forces develop across the section. Because these forces act normal to the plane of the section, the stress is called normal stress. Stress here means the average stress over the whole cross-section, not the value at one...

shearing stress

Shear Forces in Bolts and Rivets

Shearing stress is caused by transverse forces acting on an object. These forces create internal forces in the plane where the external forces are applied. The total internal force in that section is called the shear. Average shearing stress is found by dividing the shear by the cross-sectional area. This value is only an average, because shear stress is not spread evenly across the section. It can be zero at the surface and much higher than the average in other areas. Bolts, pins, and rivets...

bearing stress

Bolt-to-Plate Contact Pressure

Bearing stress is the contact pressure between two separate bodies. A common example is a bolt pushed through a plate. The bolt applies a force to the plate, and the plate pushes back with an equal and opposite force. That force is not a single point load. It is made up of many smaller forces spread across the contact surface between the bolt and the plate. Because these microforces are complex, engineers use an average value called bearing stress. Bearing stress is found by dividing the...

applications of stress

Boom and Rod Stress Analysis

Boom and rod stress analysis shows how a pinned support structure carries a load. The boom and the rod are connected by a pin and held in place by brackets and pins. The structure is then separated from its supports so the forces can be studied clearly. A free-body diagram is drawn to identify every force on the boom, the rod, and the load. The reaction forces on both members are found using equilibrium equations. At point P, the reaction causes compression in the boom. At point R, the...

stress on an oblique plane

Axial Load Stress on Inclined Sections

Axial loading creates stress in a material along its central axis. This kind of load can cause compression or elongation, and it produces normal stress. Normal stress acts perpendicular to the material area and can be either tensile or compressive. When the section is not perpendicular to the load, it becomes an oblique plane. On this inclined plane, the stress state includes both normal stress and shearing stress. Shearing stress acts parallel to the area and changes shape without changing...

stress: general loading conditions

Stress components on a loaded body can be found by cutting the body through a point with a plane parallel to the xy plane. That section carries the original loads, along with normal forces and shearing forces. The result is a simple way to describe how a structure responds under combined loading. The shearing force in the section can point in different directions within the plane. It is split into two parts that run parallel to the x and y axes. Each part is divided by the area, and as that...

components of stress

Stress Components on a Cube at a Point

Stress components on a small cube help describe how a body behaves under multiple loading. The cube is centered at point O and has stress acting on all six faces, whether the faces are visible or hidden. Normal stress components σx, σy, and σz act perpendicular to the x, y, and z axes. Shearing stress components also act on the cube faces. The visible faces carry shear stresses such as τxy and τxz. The hidden faces carry equal and opposite stresses. This balance keeps the cube in equilibrium.

design consideration

Safety Factors in Structural Design

Safety factors in structural design help engineers choose a material and loading limit that can be used safely. The process begins with a material’s ultimate strength. This value comes from tests that increase force until the material reaches its breaking point or limit. The ultimate load is then divided by the original cross-sectional area to find the ultimate normal stress, or strength. Ultimate shearing stress is another key value used in design. These limits show how much stress a material...

key terms and concepts

Learn how to find stress components on a loaded body using cuts through a point. See normal and shear stresses on xy, yz, and zx planes.

Stress Components on a Loaded Body | 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

Stress Components on a Loaded Body

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