Name: forces that bend and twist materials
Uploaded: 2025-05-22T09:06:03.000Z
Duration: 1 min 20 s
Channel: JoVE

Il momento flettente è definito come la reazione che si sviluppa in un elemento strutturale quando sottoposto a una forza esterna, provocando la flessione dell'elemento.
Quando un elemento strutturale subisce una flessione, crea forze normali di compressione sulla parte superiore e forze normali di trazione sulla parte inferiore, risultando in una coppia che determina il momento flettente dell'elemento.
La flessione di un righello fissato a un'estremità, un trampolino e il salto con l'asta sono alcuni esempi di momenti flettenti.
Un momento torsionale si verifica quando una forza di torsione viene applicata a un corpo lungo il suo asse trasversale, causando la torsione della sezione.
Strappare i vestiti, avvitare le viti e le molle di torsione sono alcuni esempi di momenti torsionali.
Le forze interne e i momenti di coppia che agiscono su una sezione trasversale di una trave possono essere rappresentati dalle loro componenti x, y e z.
Il momento torsionale, My è rappresentato lungo la direzione y, mentre Mx e Mz rappresentano le componenti del momento flettente lungo le direzioni x e z.

<ol>
	<li>Hibbeler, R.C. (2016) Ingegneria meccanica: statica e dinamica Hoboken, New Jersey: Pearson Prentice Hall, pp 344-345.</li>
	<li>Meriam, J.L.; Kraige, LG e Bolton, JN (2020). Ingegneria Meccanica \u2012 Statica. Hoboken, New Jersey: John Wiley. Pagine 276.</li>
</ol>

momenti di flessione e di torsione

Bending and Torsional Moments

I momenti di flessione e di torsione sono due concetti fondamentali nell'ingegneria strutturale. Essi svolgono un ruolo importante nel comprendere il comportamento dei materiali e delle strutture sotto diverse condizioni di carico.

La reazione sviluppata in un elemento strutturale quando viene sottoposto a una forza esterna, provoca la flessione dell'elemento. Quando un elemento strutturale si piega verso l'alto, crea forze normali di compressione nella parte superiore e forze normali di trazione nella parte inferiore, determinando così il momento flettente dell'elemento. Questo momento viene calcolato tenendo conto della distanza dal punto di interesse alla linea d'azione della forza e della sua magnitudine.

Un esempio di momento flettente è la piegatura di una riga fissa su un lato. Quando una forza viene applicata verso il basso in modo perpendicolare alla riga vicino all'estremità non supportata, induce la piegatura della riga. La forza applicata crea un momento rispetto all'estremità fissa, causando la piegatura o la deformazione della riga. In questa situazione, la riga sperimenta sia forze di compressione che forze di trazione. Il lato superiore della riga, rivolto lontano dalla forza applicata, sarà in tensione. Il lato inferiore, rivolto verso la forza applicata, sarà in compressione.

Un momento di torsione si verifica quando una forza di torsione viene applicata a un corpo lungo il suo asse trasversale o longitudinale, causando la torsione della sezione. Questa forza di torsione crea una resistenza all'interno del materiale che si oppone alla forza applicata. Il momento di torsione viene calcolato come il prodotto della forza di torsione e della distanza dal punto di interesse alla linea d'azione della forza.

Quando si avvita una vite in un materiale utilizzando un cacciavite o un trapano, si applica un momento di torsione alla vite mentre ruota e incontra la resistenza del materiale. La forza di torsione generata dal cacciavite o dal trapano fa ruotare la vite e la resistenza del materiale crea una forza contrapposta, generando così un momento di torsione.

Momenti di flessione e di torsione

I momenti flettenti e torsionali sono due concetti fondamentali nell'ingegneria strutturale. Svolgono un ruolo importante nella comprensione del comportamento di ...

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forces that bend and twist materials

Bending and torsional moments describe how materials respond to force. These ideas are important in structural engineering because they help explain how beams, rulers, and screws change shape under load. A moment depends on both the size of the force and the distance from the point of interest to the force’s line of action.

A bending moment forms when an external force makes a structural element bend. If the element bends upward, the top side is in compression and the bottom side is in tension. These opposite forces create a couple that determines the bending moment. A ruler fixed at one end shows this effect when a downward force is applied near the free end.

In that ruler example, the force acts perpendicular to the ruler and causes it to deform around the fixed end. The side facing away from the applied force is in tension, and the side facing toward the force is in compression. This makes the bending moment easy to see in a simple everyday object.

A torsional moment happens when a twisting force is applied along a body’s transverse or longitudinal axis. The material resists that twist, so an internal force develops inside it. A screwdriver or power drill turning a screw shows torsion in action. As the screw rotates and meets resistance from the material, the twisting force and the opposing resistance create the torsional moment.

Forces That Bend and Twist Materials

sign convention

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Beam analysis depends on the internal forces and moments inside a structure. These include normal force, shear force, and bending moment. Engineers use the method of sections to cut the beam and find these values. A sign convention helps show whether each result is positive or negative. Normal force acts perpendicular to the beam’s cross-section. It can pull the material in tension or push it in compression. Tension is taken as positive, while compression is taken as negative. This makes it...

normal and shear force

Beam Loads and Internal Forces

Beam loads create internal forces inside a structure. Weight, pressure, and other external forces can all act on a beam. These internal forces affect the beam’s stability and strength. Engineers study these forces to find their size and direction. A common approach is the method of sections. In this method, an imaginary cut is made at a chosen point on the beam, and the forces at that section are analyzed. One internal force is the normal force, also called the axial force. It acts...

bending and torsional moments

Bending and torsional moments describe how materials respond to force. These ideas are important in structural engineering because they help explain how beams, rulers, and screws change shape under load. A moment depends on both the size of the force and the distance from the point of interest to the force’s line of action. A bending moment forms when an external force makes a structural element bend. If the element bends upward, the top side is in compression and the bottom side is in tension.

internal loadings in structural members: problem solving

internal-loadings-in-structural-members-problem-solving

Beam Internal Force Analysis at Point A

Beam internal force analysis shows how normal force, shear force, and bending moment act inside a structural member. These internal loadings help engineers check whether a beam can support the external forces applied to it. The example uses a beam OC that weighs 5 kN and is inclined at 53.13° with the horizontal. The beam is supported at both ends. The goal is to find the internal loadings at point A. The first step is to find the reaction force at point C. This is done by taking the moment...

beams

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Beams are key parts of structural engineering and construction. They support loads that act at different points along their length. Engineers use beam shape and support conditions to understand how a beam will perform. Beams can be classified by geometry. Straight beams are the most common and have a constant cross-section along their length. Tapered beams change in cross-section from one end to the other, while curved beams have a curved shape. Beam cross-section also matters. Common shapes...

shear diagram

Beam Shear Force Diagram

Beam shear force diagrams show how shear changes along the length of a supported beam. In beam mechanics, they help students track the internal shear force caused by perpendicular loads. The beam AB in this example is supported at both ends, so the first step is to draw a free-body diagram that shows the external forces and internal reactions. The reaction forces at supports A and B are found with equilibrium equations for force and moment. For the beam shown, the vertical reaction at A is 24...

bending moment diagram

Beam Load Analysis with Moment Diagrams

Beam load analysis uses a bending moment diagram to show how bending changes along the length of a beam. This diagram helps engineers and designers check whether a structure can handle applied forces. It is also useful for parts such as shelving arms, which must resist forces and moments from a load. To build the diagram, start by finding the reactive forces and any couple moments on the beam. In some cases, especially when a beam is inclined, these forces must be resolved into components that...

relation between the distributed load and shear

relation-between-the-distributed-load-and-shear

Shear Change Under Distributed Loading

Shear force changes along a beam under a distributed load. In structural analysis, this relationship helps explain how beams respond to loading conditions that also include concentrated loads and a couple moment. To study the link, consider a small beam section that has no concentrated load or couple moment on it. Draw a free-body diagram for that elemental section. It includes the distributed load along the beam, the shear force V(x) on the right-hand side of the cut, and a small added shear...

relation between the shear and bending moment

relation-between-the-shear-and-bending-moment

Shear and Moment Diagrams in Beam Loads

Shear and moment diagrams help show how a beam responds to loads. A beam can carry a distributed load, concentrated loads, and a couple moment. These loads create internal shear forces and bending moments. The beam is examined by isolating a small elemental section and drawing a free-body diagram. For that section to stay in equilibrium, the moment on the right side must be slightly larger than the moment on the left side. The distributed load also has a resultant force that acts at a...

shear and bending moment diagram: problem solving

shear-and-bending-moment-diagram-problem-solving

Beam Load Analysis with Shear Diagrams

Beam load analysis uses shear and bending moment diagrams to track the internal forces in a beam. These diagrams are important when a beam carries concentrated loads and a distributed load. They help show how the beam responds so structures can be designed safely and efficiently. The first step is to draw a free-body diagram of the whole beam. A free-body diagram shows the concentrated loads, the distributed load, and the reaction forces at the supports. Use the equilibrium equations, where...

cable subjected to concentrated loads

Finding Tension in a Loaded Cable

Flexible cables can carry vertical point loads between two fixed supports. The cable is treated as flexible, inextensible, and nearly weightless. Under these conditions, it changes shape to form straight-line segments, and each segment carries a constant tensile force. To analyze the cable, a free-body diagram is drawn for the whole cable. This helps identify the reaction forces at the supports. In many cases, the number of unknown reaction components is greater than the available equilibrium...

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Finding Cable Shape Under Distributed Load

Cable shape under a distributed load is found by analyzing the forces along a small piece of the cable. This method is important in suspension bridge design because the main cables must carry changing loads safely. The load causes the tensile force in the cable to change, and it also creates cable deformation. The analysis starts with a free-body diagram of a short cable segment. The diagram shows the distributed load and the change in tensile force across that segment. Equilibrium equations...

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Cable Sag Under Its Own Weight

Overhead power transmission cables sag under their own weight, and that shape affects how they carry electricity across long distances. To study this behavior, the cable is analyzed with a generalized loading function. This function treats the load along the cable's arc length instead of its projected length, which gives a more accurate picture of the cable's response. The analysis then focuses on a small cable segment. A free-body diagram is drawn to show the forces acting on that segment.

cable: problem solving

Cable Tension Under Uniform Loading

Cable tension under uniform loading is found by analyzing a cable fixed between two supports. The problem starts with the support conditions and the load on the cable. From there, the cable’s shape must be described with an equation that matches the curve formed by the load. The next step is to integrate the shape equation to get the cable’s shape function. This makes it possible to solve for constants in the equation. The boundary condition at the origin gives one constant. The slope, which...

key terms and concepts

Explore how bending and torsional moments act on materials, from a ruler bending at one end to a screw twisting under a screwdriver.

Forces That Bend and Twist Materials | 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

Forces That Bend and Twist Materials

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