Structural Mechanics and Mechanical Systems Explained

Structural Fundamentals

Structure: A set of elements designed to withstand loads, preventing the body from breaking or deforming excessively.

• Stability: The center of gravity must be located at the base of the structure to prevent tipping. Stability can be increased by adding mass to the base.
• Resistance: The ability of a structure to bear stress without breaking, which depends on the quantity and type of material used.
• Rigidity: Achieved by welding joints and triangulating bar structures (the triangle is the only non-deformable geometric figure).

Internal Forces

Effort: The internal tension experienced by bodies subjected to one or more external forces. Types include: tension, compression, bending, twisting, shearing, and buckling.

Classification of Mechanisms

• Motion Transmission Mechanisms: Transmit motion produced by a driving element to another location.
• Motion Transformation Mechanisms: Transform circular motion into rectilinear motion or vice versa.

Levers and the Law of the Lever

A lever is in equilibrium when the product of the force (F) and its distance (d) from the fulcrum equals the product of the resistance (R) and its distance (r) from the fulcrum. This is known as the Law of the Lever: F × d = R × r.

There are three classes of levers: first, second, and third grade.

Hoists and Pulleys

A hoist is a specialized assembly of fixed and mobile pulleys. The formula is: F = R / 2n.

Gears and Transmission Systems

Wheels and Gears

Gears are wheelsets with protruding teeth that mesh together to transmit motion. Types include cylindrical (straight or helical teeth) and conical gears. They are widely used in industrial machinery, automotive parts, and household appliances.

Chain and Belt Systems

• Chain Gear Systems: Consists of two parallel shaft gears connected by a metal chain or a toothed neoprene belt, allowing them to rotate simultaneously.
• Belt Pulley Trains: Circular motion is transmitted from axis 1 to axis 2 via pulleys connected by a tight strap.
• Gear Trains: Circular movement is transmitted from the first axis to the second through wheels 1 and 2. Wheel 3 rotates with wheel 2 to transmit movement to wheel 4.

Circular to Linear Motion Transformation

• Crank-Connecting Rod: Consists of a crank and a bar called a connecting rod.
• Crankshaft: A series of rods placed on a single angled shaft; each elbow acts as a crank.
• Eccentric: A wheel where the rotational axis does not coincide with the center of the circle. It transforms rotational motion into reciprocating linear motion. The distance between the center and the axis of rotation is called eccentricity.