Mr. Rogers' IB Design Technology Objectives
Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter
Design Project Materials Product Development Product Design

Topic 4 Materials

Unit Plan Practice Test Study Guide

Objectives
Essential Question: How can materials be described?

Introducing and Classifying Materials

  1. Define

  • atom

  • molecule

  • alloy

  • composite.

  1. Describe and differentiate between the three main types of bond (attraction between atoms):

    • ionic

    • covalent

    • metallic.

     

  2. State that materials can be classified into groups according to similarities in 
their microstructures and properties.
  3. Explain that several classifications are recognized but that no single 
classification is “perfect”.
  4. State that materials are classified into groups: 
  • timber - natural wood or composite (plywood, masonite, particle board)
  • metals - ferrous (iron or iron alloys) or nonferrous
  • ceramics - earthenware, porcelain, stoneware, and glass
  • plastics - thermoplastics or thermosets
  • textile fibers - natural or synthetic
  •  food - vegetable or animal origin
  • composites - fiber glass, carbon fiber

Assessment -- Materials Vocabulary

IB Standard: Various (see objectives 1 and 2 above).

Specifications: Write definitions for the terms in objectives 1 and 2

Deliverable: Place the completed Word file in the IB Design Technology folder of your student drive.

Work Group: individuals.
Essential Question: What makes a material appropriate? 
Properties of Materials (4h)
Physical Properties
  1. Define the physical properties of: 
  • density
  • electrical resistively
  • thermal conductivity
  • thermal expansion - important if joining dissimilar materials
  • hardness - resistance to penetration or scratching 
  1. Explain a design context where each of the properties above is an 
important consideration.
 
Essential Question: Does form follow function? 
 
The Engineering Context -- a specialized area of the design context
Mechanical and civil engineers are the primary types concerned with mechanical parameters like stress, strain, stiffness, elastic stability, etc. Mechanical engineers use this type of information to design the structure for aircraft, pressure vessels, and all kinds of different machines. Civil engineers use it for designing buildings, bridges , and other types of structures.

Engineers are primarily concerned with the safety,  function, and practical aspects of design rather than the aesthetics.
 
  1. Define stress and explain how it is different from pressure although both use the same units.
  • Stress = (force) / (unit of area) at any given point inside an object
  • Pressure = (force) / (unit of area) applied to the outside surface of an object
  • Pressure is an external load. Stress is an internal condition resulting from external loads of forces and pressures. The stress inside a structure can be orders of magnitude higher than the external pressure loads applied to it.

Relevance: Misconceptions about basic engineering principles are the life blood of conspiracy theorists. These conspiracies include the Murrah Federal Building bombing, the Twin Towers collapse on 9-11, and the Kennedy assassination. Conspiracy theories sometimes gain enough momentum to trigger government investigations costing millions of dollars. While this is not inherently harmful, it is a waste of funds when the theories are based on engineering or scientific nonsense.

  1. Define strain: the ratio of a change in dimension to the original value of that dimension.

Strain = (change in length) / (original length)

  1. Mechanical Properties

  • tensile strength - the amount of tensile stress a material can withstand before failure

    • yield stress - max stress before permanent deformation

    • ultimate tensile stress - max stress before catastrophic failure

    • rupture stress - max stress at catastrophic failure

  • stiffness - modulus of elasticity or Young's modulus. Note, Young's modulus is a material property. The stiffness of a structure depends on both the material and the design. Area moment of inertia (see 18 below) is a key design related indicator of stiffness.

  • toughness - resistance to abrasion and cutting. Work required to make a material fail catastrophically. Tough materials are generally not brittle.

  • ductility - ability to extrude

  • malleability - ability to shape plastically. Note: the IB syllabus makes a special point to make a distinction between ductility and malleability. For all practical purposes, ductile materials are also malleable.

  1. Explain a design context where each of the above properties is an important consideration.

  1. Draw and describe a stress/strain graph (see at right)

  • elastic region

  • yield stress

  • plastic flow region

  • ultimate stress (UTS).

 

 

Essential Question: What keeps a building from falling down?
  1. Explain the relationship of the 2 most common structural members (beams and columns).
  • Beams : typically horizontal structural members designed especially to resist bending moment and shear loads. (Note: moment arm = distance from load to pivot point.)
  • Columns: vertical structural members designed especially to resist compression loads
  1. Identify types of load.
         
Compression/Tension: compression is squeezing together. Tension is pulling apart. Compression can be considered negative tension.
Shear: forces moving in opposite directions on each side of an element similar to the action of a pair of scissors or shears.
Bending Moment: a twisting action
  1. Calculate factor of safety .

Factor of safety) = (Design load) / (normal maximum load)

  1. Explain why factor of safety is important.
  • uncertainty about normal maximum load: a designer has to make an educated guess about what the maximum load will be.
  • fatigue cracks: caused by the cycling if stresses particularly fro tension to compression. Some materials such as steel have a fatigue limit. If the stress is kept below the fatigue limit a crack will never form. Cracks grow larger over time until catastrophic failure.
  • corrosion
  • fire
  • shock loads

 

Assessment -- Investigation of conspiracy theories about the bombing of the Alfred P. Murrah Federal Building

IB Standard: Various including stress, strain, stiffness, beams, factor of safety etc..

Specifications: Research the bombing of the Alfred P. Murrah Federal Building and locate a conspiracy site about it.

  1. Write a paragraph describing what happened and give your source including the url.
  2. Write another paragraph using non-conspiracy theory sources describing why the building collapsed and give your source including the url..
  3. Write a third paragraph summarizing a conspiracy theory about the collapse and give your source including the url.
    4.
  4. Write a final paragraph explaining the flaws in the above conspiracy theory. Use the vocabulary and knowledge you have gained concerning materials, such as,  stress and strain, external loads vs. internal stresses etc.

Deliverable: Place the completed Word file in the IB Design Technology folder of your student drive. Call the file: Murrah Investigation <your name>.

Work Group: individual.

 

Essential Question: Why is stiffness important in structures like bridges, buildings, wings, etc.?
  1. Calculate the stiffness of a structure. Relevance: Stiffness is a critical characteristic of structures that determines not just safety and function but also the emotional response of users. For example a flexible floor in a multi-story building.

stiffness = (load) / (deflection)

  1. Explain how both modulus of elasticity and moment of inertia are related to stiffness.
  • Modulus of elasticity or Young’s modulus (a material property) - directly proportional to stiffness
  • Area Moment of inertia (a design property) - directly proportional to stiffness

  1. Calculate the Young’s modulus of a material.

    (Young’s modulus) = stress / strain

  1. Calculate area moment of inertia for a beam with a rectangular cross section. Area moment of inertia is a key design related indicator of stiffness. The higher the number the stiffer the structure.
I 0 = (bh3) / 12
 
where:
I 0 = Area Moment of Inertial for a rectangular cross section of a beam
b = width
h = height in the direction of the load
  1. Define elastic stability (the tendency of a structure to resist buckling) and state why it is an important consideration in design.
  2. Give examples of elastic instability.
  • External pressure applied to a plastic soft drink bottle's exterior
  • Long thin columns

 

Assessment -- Investigation of relative stiffness of beams

IB Standard: Various including stiffness and beams.

Specifications: Find dimensions for a 2x4, 2x6, 2x12 made of lumber. Calculate the relative stiffness (area moment of inertia) of each beam in both its strongest and weakest position. From a stiffness and load standpoint, explain why 2x4s are generally used in walls, 2x6s in ceilings, and 2x8s or 2x12s in floors as the structural members.

Deliverable: Place the completed Word file in the IB Design Technology folder of your student drive.

Work Group: individuals.

 

Aesthetic characteristics

  1. Outline the characteristics of taste, smell, appearance, texture and color.
  2. Explain a design context where each of the above characteristics are an
    important consideration.

 

 The IB Properties/Materials Matrix

  1. Explain how all the groups and sub-groups of materials shown above can be
    organized into a properties/materials matrix
  2. Explain the relative values of the properties in the IB properties/materials
    matrix    .

 

Assessment: Unit exam objectives 1-24
 
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