Biomechanical+Testing+Lecture

Biomechanical+Testing+Lecture - 125:315 Lab: Biomechanical...

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125:315 Lab: Biomechanical Testing Objectives The objectives of this laboratory experiment are: 1. Understanding of mechanical testing machine. 1. Goals of the tests 2. Familiarity with its basic controls and functions. 3. Limitations, errors and expectations. 2. Application in Fracture Fixation Evaluation 1. Composite structure Issues 2. Young’s elastic modulus (E) of a material 3. Flexural rigidity (EI) of a structure 4. Are results meaningful?
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Mechanical Testing System Load Cell Measures load in lbs or N Linear Actuator Measures displacement in inches or mm Perform calibration, initialize software set-ups, and insert the appropriate jigs. After the test, load vs. time and displacement vs. time are recorded. What is next? Depends on what questions are asked. PC with the hardware specific software
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Material Properties Four Point Bending Test Three Point Bending Test Tensile Test Torsion Test
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From 125:208 Course: Mechanical Testing Tensile or compression test: 1. Mechanical Testing machine such as Instron is used to apply a displacement to one end of the sample. The computer records how far the grip (and thus one end of the sample) has moved. 2. The other end of the sample is fixed (doesn’t move)and is attached in series to a force transducer that converts force to voltage that can be measured with an analog-to-digital converter (somewhere in the instrumentation). The force is also recorded by the computer. 3. The sample deformation (change in displacement) is recorded. Measure the gage length of the sample, and calculate the engineering strain: ε = δ / L 0 (deformation / Initial length) 4. The force in the material to resist that deformation is recorded. The cross- sectional area of the sample is measured, to calculate the engineering stress: σ = P / A 0 (Load / Initial area) E = σ / ε Modulus of Elasticity
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Material Properties
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P P L 0 δ A 0 yield δ O K P B ε O E σ σ u Axial compression Load deflection curve Stress Strain Curve Original length L0 ; Original Area A0 Measured Stiffness K = P/ δ σ = E ε ; E = σ/ ε σ σ = P/Ao and
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Biomechanical+Testing+Lecture - 125:315 Lab: Biomechanical...

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