Mechanical Behavior, Testing, and Properties of Materials (l.u )

Material Behavior  Most manufacturing operations = Mechanical deformation of materials  Materials may behave/respond to the applied forces  In use, a part/product may be subjected to external forces that affect performance  Various tests help determine response/behavior Engr 2411

Tension (elongation)  Most common test for determining the mechanical properties of materials (strength, ductility, toughness).  Determines relationship between stress and strain the material withstands when subjected to pulling force Engr 2412

Tension  Pulling force can reveal materials strength and ductility  Engineering Stress: ratio of load to cross-sectional area. Stress = force over area (usually measured in Force F, lbs, or pressure P – MPa or psi)  Engineering Strain: elongation. Strain = amount of compression or stretch (mm, inch) Engr 2413

Tensile Testing  Tensile Test AL Tensile Test AL  Tensile Test Steel Tensile Test Steel  Tensile Test Nylon Tensile Test Nylon Engr 2414 (

Tension - Ductility  Ductility: extent of plastic deformation a material undergoes prior to fracture  Ductility is the strain of the material ○ Elongation ○ Reduction of Area  Ductility in steel Ductility in steel  Ductility in steel Ductility in steel Engr 2415

Tension (strain X vs stress Y) Engr 2416

Tension  True Stress: ratio of load to actual cross-sectional area.  True Strain: instantaneous elongation.  Used to reveal n factor – strain hardening of material (higher n = stronger and harder material becomes as it is strained)  Tensile Strength: Maximum Engineering Stress (UTS) – max force per area a material can withstand.  Modulus of Elasticity E (Young's Modulus): material stiffness. Engr 2417

Compression  Carried out by compressing a cylindrical specimen between two flat plates (opposite to Tension).  Cross-sectional area of the specimen changes along its height, being maximum at the center.  Concrete Testing Concrete Testing  Concrete Testing Concrete Testing Engr 2418

Compression Engr 2419 Barreling: consequence of friction

Torsion Test  Used to determine shear stress.  Tension & Torsion Test Tension & Torsion Test Engr 24110

Bending Test  Preferred method for testing brittle materials, which are normally difficult to shape and to clamp. rectangular cross section specimen, supported at ends. vertical load. tensile and compressive stresses present in the specimen.  Bend test of HDPE Pipe Bend test of HDPE Pipe  Automated Press Brake Automated Press Brake Engr 24111

Bending Test 12Engr 241 ( Shear Test of Concrete Beam

Hardness  Common test for assessing mechanical properties of materials, by determining resistance to scratching or indentation. Depends on shape of indenter and load. Standard Tests (Brinell, Rockwell, Vickers, Knoop, Mohs)  Hardness Test of Model 98 Hardness Test of Model 98 Engr 24113

Rockwell Hardness ( Engr 24114

Hardness Brinell ○ 500, 1500, 3000 kg load ○ 10mm ball Vickers ○ kg load ○ 136° diamond Knoop ○ 25 g - 5 kg load ○ pyramid diamond Mohs ○ 1 talc to 10 diamond ○ Scratch test Engr 24115

Rockwell Hardness  Most used and versatile test (measures depth of penetration)  1/16“ hardened steel ball, B scale (100 kg), F scale (60 kg), G scale (150 kg)  1 /8“ hardened steel ball, E scale (100 kg)  Diamond Cone, C Scale (150 kg), A Scale (60 kg), D Scale (100 kg) Engr 24116

Creep Gradual shifting: Displacement (in construction, this is called slump) In metals, elongation after a period of time – Plastic deformation due to dislocation of crystal boundaries (necking) Engr Land Creep – ( Glass Creep

Creep (physics = fusion, change of state) Engr 24118

Fatigue Cyclic stresses caused by fluctuating mechanical loads Fatigue Test on Airplane blade Shear Fatigue Test on Metal Wall Fatigue Test of Structural Steel Engr (

Fatigue Road fatigue Engr (training.ce.washington.edu)

Pre-fatigue - Stress Corrosion Cracking Accelerated by environmental factors – heat, moisture, chemicals, salt In metals, stresses relieved by annealing Engr Stress Corrosion Cracking in 300 series SS Stress Corrosion Cracking in 300 series SS (

Fatigue Test Repeat load on automobile leaf springs Engr (

Toughness  Strength and ductility (both height + width of stress-strain curve Engr (

Impact Test  Toughness (strength and ductility)  Light bulb Impact Light bulb Impact  Window Impact Window Impact Engr (

Residual Stress  After processing, materials can undergo residual stress  Stresses that remain within the part after it has been formed and all external forces have been removed. Tensile vs. compressive stresses Stress Cracking Stress-Corrosion Cracking  Residual stresses may be reduced by annealing or by further deformation. Engr 24125

Residual Stress  Liberty bell Engr

Annealing ( Engr ( Annealing is commonly used on parts that have been cold worked or heat treated. Annealing is commonly used on parts that have been cold worked or heat treated.

Material Failure  When is material failure good/desired?  What are catalysts/causes for material failure?  What are material properties that influence material failure?  Gallopin' Gertie Gallopin' Gertie Engr 24128

Topic Support  Material failure in electrical generating equipment  Material Defects in Jewelry - struck.htm struck.htm Engr 24129