Mechanical Properties & Electrical Installations Overview

Posted on Nov 21, 2024 in Technology

Mechanical Properties of Materials

Materials exhibit various mechanical properties in response to external forces, opposing internal cohesion forces. These properties are measured through material testing, including:

  • Tensile (Stretching)
  • Compression (Crushing)
  • Flexion (Bending)
  • Torsion (Twisting)
  • Shear (Cutting)
  • Plasticity
  • Toughness

Key mechanical properties include:

  • Mechanical Resistance: Capacity to withstand efforts without deforming or breaking.
  • Tenacity: Resistance to shock.
  • Fragility: Ease with which a material breaks or twists.
  • Elasticity: Maximum limit of a material to deform elastically.
  • Plasticity: Ability to deform permanently without breaking.
  • Hardness: Resistance to being scratched or penetrated.

Other concepts include:

  • Unit Stress: Force divided by area (F/A).
  • Unit Elongation: Relationship between the elongation of a piece and its initial length.
  • Necking: Decrease in the cross-section of a sample due to tensile effort.
  • Stiffness: Resistance to deformation.
  • Density: Intrinsic characteristic relating mass to volume.
  • Relative Density: Ratio of a material’s density to that of water at 4°C.

Hardness Testing

Compares and measures the hardness of various materials.

Resilience Essay

Calculates a material’s resistance to breaking by impact (Charpy and Izod tests). Formula: K = ec / A.

Mechanical Fatigue

Alternating stress applied repetitively or cyclically over time, simulating actual working conditions.

Fatigue Limit

Maximum stress value at which a material does not break over an infinite number of cycles.

Thermal Expansion

Depends on the material and temperature. It can be linear, surface, or cubic. Formulas: ΔL = α * L0 * ΔT (linear), ΔA = 2α * A0 * ΔT (surface), ΔV = 3α * V0 * ΔT (volume).

Unions and Fasteners

Types of Unions

  • Fixed
  • Removable

Thread Types

  • Triangular (Screw): Whitworth, ISO
  • Square: Machine spindles (deprecated)
  • Trapezoidal: Similar to square
  • Serrated Teeth: For high impact
  • Round: For contact with soil, dirt, or high temperatures

Characteristics of Threads

  • Nominal Diameter (D): Outer diameter of the screw.
  • Step: Distance between threads.

Torque

Torque (τ) = Force (F) * Distance (C) or Force (F) * Radius (r).

Clavets (Keys)

Parts located within notches for specific geometry and axis alignment. Types include pins, transverse, longitudinal, reeds, and fluted shafts.

Tabs

Allow axial displacement while transmitting movement.

Striated Axes

Shafts with equally spaced notches for fitting into a docked piece, transmitting torsional effort or torque.

Springs

Elastic materials that deform under force, absorbing energy and restoring to their original shape. Types include tensile, compression, torsion, spiral, crossbow, and rubber.

Bearings

Mechanical elements mounted between two bodies to allow rotation with minimal friction. Components include inner and outer rings, rolling bodies, and separators.

Lubrication

Reduces friction between machine elements. Types include:

  • Hydrodynamic Lubrication: Maintains a lubricant film between parts.
  • Synthetic Lubrication: Uses molecules of the same size and configuration, offering energy savings and increased durability.
  • Grease Lubrication: Uses grease instead of mineral oils for low-speed applications.

Low Voltage Electrical Installations

Regulations

Establish technical conditions and safety guarantees for electrical installations.

Types of Installations

  • Exterior Lighting: Public spaces.
  • Domestic: Residential buildings.
  • Industrial: Manufacturing or product handling buildings.
  • Public Access: Buildings with general public access.

General Components

  • Connection Points: Inner and outer branches.
  • Branch: Installation between the distribution network and safety protection.
  • General Supply Lines: Connect the meter box to the building’s centralization.
  • Meter: Measures power consumption.
  • Derivation: Power line connecting the meter to the control and protection panel.
  • Interior Installation: Control box, protection circuitry, and ground connection.

Protection Devices

  • ICMP: Maximum power control switch.
  • IGA: Automatic general switch (overload protection).
  • ID: Differential switch (protects against contact).
  • PIA: Magnetothermic switch (protects against small overloads and short circuits).
  • DPS: Surge protector.

Electrification Levels

  • Basic: Minimum of 5 circuits for equipment use, up to 5750W at 230V.
  • Elevated: 5+ circuits, up to 9200W at 230V.

Domotics

Automation and control of private installations for improved quality of life and convenience.

Power Factor

Determined by the type of receiver connected to the network, representing the shift between current and voltage. Formula: cos(φ) = Wa / Wap.