Science notes on constraints and deformation

CONSTRAINTS AND DEFORMATIONS

  • Technical objects are designed for specific purposes.
  • Parts of technical objects may face external constraints or forces that cause deformation.
  • Deformation can lead to:
  • Temporary change
  • Permanent change
  • Material breakage

CONSTRAINT DEFINITION

  • Constraint: An external force exerted on materials that tends to deform them.
  • Manufacturers must assess potential stress and deformations to choose appropriate materials.

TYPES OF CONSTRAINTS

  1. Compression: A force that squeezes a material.
  • Example: Pushing together two ends of a spring.
  1. Tension: A force that stretches a material.
  • Example: Pulling on a rope.
  1. Torsion: A twisting force applied to an object.
  • Example: Twisting a bottle cap.
  1. Deflection: A bending force that causes a member to deviate from its original shape.
  • Example: A beam bending under a load.
  1. Shearing: A force applied perpendicular to the material, causing layers to slide past each other.
  • Example: Cutting with scissors.

MECHANICAL PROPERTIES OF MATERIALS

  • Mechanical properties explain how materials react under constraints.

KEY MECHANICAL PROPERTIES

  • Stiffness: Resistance to deformation when a force is applied.
  • Example: Plastic maintaining shape under twisting.
  • Hardness: Resistance to indentation or abrasion.
  • Example: Wood flooring resisting shoe heel indentations.
  • Ductility: Ability of a material to stretch without breaking.
  • Example: Metal wire stretching without snapping.
  • Resilience: Capacity to absorb energy when deformed and return to original shape.
  • Example: Boat hull resisting impact.
  • Elasticity: Ability to bend and return to original shape.
  • Example: Eavestroughing that bends easily.

TECHNICAL DRAWINGS

  • After selecting materials for a technical object, a drafting (technical drawing) phase is necessary.

DRAWING PROJECTIONS

  • Orthogonal Projection: 2D representation showing multiple views (top, front, side).
  • Axonometric Projection: 3D view drawn on a grid forming 120º angles.
  • Exploded View: Shows all component parts separated for clarity.
  • Cross-Section: Represents the interior by depicting a cut through the object.

DIMENSIONAL TOLERANCE

  • Due to manufacturing imperfections, actual sizes can differ from drawings.
  • Tolerance: Acceptable margin of error for dimensions in drawings.
  • Example: A dimension of 4.27 ± 0.04 mm indicates a range of sizes from 4.23 mm to 4.31 mm.

FUNCTIONAL DIMENSIONING

  • Components must fit together correctly; tolerances must be respected.
  • Necessary space for component movement is called play.

MATERIALS

WOOD

  • Sourced from processing trees.
  • Hardwoods: From deciduous trees (e.g., maple, oak) - often harder.
  • Softwoods: From coniferous trees (e.g., pine, spruce) - generally softer.
  • Modified woods increase versatility and stability.
  • Plywood: Layers of wood glued together.
  • Particleboard: Wood chips fused together.

METAL

  • Extracted from mineral ores, metals are shiny and conductive.
  • Pure Metals: Chosen for specific uses (e.g., Copper for wires).
  • Metal Alloys: Mixed metals that enhance properties (e.g., Steel for strength).

PLASTICS

  • Derived from fossil fuels, plastics are categorized into:
  • Thermoplastics: Can be reshaped multiple times when heated.
  • Thermosetting Plastics: Shaped once and harden permanently.

CERAMICS

  • Solid materials made by heating inorganic compounds.
  • Properties include hardness, low conductivity, and heat resistance.

COMPOSITES

  • Combination of different materials to enhance properties.
  • Example: Carbon-fibre used in airplanes for its strength and light weight.

MATERIAL DEGRADATION AND PROTECTION

  • Materials can degrade over time due to environmental factors.
  • Strategies to prevent degradation include:
  • Wood: Varnish, treated wood to resist rot.
  • Ceramics: Coating, careful handling to avoid thermal shock.
  • Plastics: Waterproof coatings and additives to resist UV damage.
  • Metals: Coatings like galvanization to prevent rust.