CMT- Lesson 8

• Wood


  An organic material, a natural composite of CELLULOSE FIBERS (which are strong in tension) embedded in the matrix of lignin which resists compression
• Common forms of wood

  • Natural Wood
  • Engineered Wood
• Natural Wood


  Products that are HARVESTED DIRECTLY from trees, do not experience any fundamental changes
• Engineered Wood


  Woods that are made from natural wood that has been ALTERED in a fundamental way so as to change the characteristics of the wood it was made from
• Bend Testing


  1. Measure the behavior of materials subjected to simple beam loading
• Modulus of Rupture


  The MAXIMUM LOAD carrying capacity of wood sample
• Modulus of Elasticity


  Helps in determining the flexural stiffness and modolus of elasticity properties of wood based materials
• ASTM D143 static bend test


  Calls for the use of bearing plates on articulating KNIFE EDGE support rollers to reduce risk of load concentrations
• Tensile Test


  1. Detect how a material resists loaded tensile forces until it fractures
• Tensile Strength


  Describes how much load a material can withstand when loaded in tension
• Compression Test

  • Opposite of tensile testing
• Compression Strength


  The maximum load a material can withstand without crushing or rupturing when loaded in compression
• Shear Test

  • a strength test to identify the reaction to shear stress, modulus, and strain of test samples
• Types of materials for shear testing

  • Rigid Substrates
  • Adhesives
  • Layered Composites
• ASTM D143 Wood Shear Parallel to Grain


  Allows the shear strength values to be obtained free from influence of WOOD DEFECTS
• Oven dry testing


  The OLDEST and MOST ACCURATE method for measuring the moisture content of wood
• Moisture meter testing


  The FASTEST way to test the moisture content of wood
• Bend Testing is sometimes called flexure testing or transverse beam testing.
• 3 Point Bend Test - test that provide values for the modulus of elasticity, flexural stress, flexural strain, and the flexural stress strain response of the material
• Rigid Substrates

  • composed of metals, plastics, CERAMICS, composites or woods
  • usually come in a solid form and are used as building materials or fasteners.
• Adhesives - USED TO BOND two materials together and experience shear stress when the materials are pulled in opposing directions in an attempt to slide them apart.
• Layered Composites - experience shear stress in a similar manner to adhesives as the shear forces are applied to the GLUE OR LAMINATE used to hold the layers together.
• Shear tests are used in RHEOLOGY, quality control, material development, adhesives, and structural engineering
• Tension parallel to grain

  • tensile strength is FAR IN EXCESS of other strength properties
• Tension perpendicular to grain

  • tensile stress distribution is UNEVEN and lower values are observed
• Compression parallel to grain

  • the wooden sample shows a RELATIVELY HIGH compressive strength
• Compression perpendicular to grain

  • the samples fails at RELATIVELY LESS load value