Structures and mechanism

Structures and mechanism

1. Structures definiton and types

   • Mass structure: These are solid, heavy and very sturdy structures. Examples include walls, dams, etc.
   • Frame structures. These structures are formed by columns and beams that act as supporting elements. One example might be the structure of a building.
   • Truss structures. These structures are composed of bars that form triangles. They are lightweight and sturdy. Examples include cranes, electricity pylons, etc.
   • Suspended structures. These are held in place by cables and suspenders attached to sturdy supports. Examples include suspension bridges, tents, marquees, etc.

2. . Types of stress

   • Compression: This is caused by forces acting on a body that tend to flatten it or reduce its length or thickness.
   • Tension: This is caused by forces acting on a body that tent to stretch
   • Bending: This is caused by forces acting on an element that make it curve or bend.
   • Torsion This is caused by forces acting on a body that make it twist.
   • Shear:This is caused by two equal forces applied in opposite directions that act on lines of action close to each other.

3. Conditions for strong structures

   • Rigidity: If a material is rigid, it does not change shape when force is applied to it.
   • Equilibrium: A body is in equilibrium when its structure remains stationary. There are two types of equilibrium: stable and unstable.
   • Stability:A body is in stable equilibrium if it does not move when a force is applied to it.

4. Machines and mechanisms

   • Driver element: feeds energy to the machine Driven element: receives the force produced in the machine . Converting and/or transmitting element:
   • The types of motion that can be converted by mechanisms are: Linear motion: the object moves in a straight line. Rotary motion: the object moves in circles. For example, a turning water-wheel. Reciprocating motion: the object moves forwards and backwards in a straight line. Oscillating motion: the object moves backwards and forwards tracing a curve.

5. Simple machines: linear transmission mechanisms

   • Class 1 levers The fulcrum is located between the weight or resistance to overcome and the point where the force is applied. Examples include a crowbar, see-saw, pliers, scissors, oar, etc.
   • Class 2 levers The fulcrum is at one end of the lever and the effort is at the other end. The resistance to overcome is located between the fulcrum and the effort. Examples include nutcrackers, wheelbarrows, paper punch, etc.
   • Class 3 levers The effort is located between the fulcrum and the resistance. Examples include tweezers, kitchen tongs, staple removers, etc.
   • E · Ae = R · Ar
   • Pulleys
     • a) For the fixed pulley, F = R = 100 N. An effort of 100 N is required. b) For the mobile pulley, estilo tamaño 12px F espacio igual fracción R entre 2 igual fracción 100 entre 2 igual 50 N fin estilo. We reduce the required effort to half. c) For the hoist, with four pulleys, estilo tamaño 12px F espacio igual fracción R entre 4 igual fracción 100 entre 4 igual 25 N fin estilo. We reduce the required effort to one quarter.

6. Rotary transmission mechanisms

   • Friction wheels are a set of two wheels located one next to the other.
     • i=W1/W2=D1/D2 W= Velocidad rpm D= diametro
   • Bet and pulleys sistem
     • This system is made up of two pulley wheels joined by a belt that slots into the grooved rim of the wheels.
   • Gear
     • A gear is a mechanism consisting of two wheels with teeth.
       • i=w1/w2=Z1/Z2 W= Velocidad rpm Z= dientes del engranaje
     • Chain and sproteck
       • These systems consist of two toothed wheels (sprockets) separated by a distance and connected by a chain
     • Worm gear
       • These systems consist of two toothed wheels (sprockets) separated by a distance and connected by a chain
       • i= Z1/Z2 Z1= 1

7. Motion mechanism

   • Screw and nut
     • This mechanism consists of a screw and a nut.
   • Rack and pinion
     • This mechanism consists of a toothed wheel (pinion) that meshes with a toothed bar (rack). The rotary motion of the pinion is converted to linear motion in the rack.
   • Crak and slider
     • This mechanism consists of a rigid bar (connecting rod) that is connected at one end to a crank.
   • Cams
     • Cams are usually elliptical in shape. They are attached to a shaft (driver) and, as they rotate, they drive an element called the follower. A spring keeps the follower in permanent contact with the cam.
     • Eccentric cam
       • An eccentric cam is a mechanism similar to a regular cam.