Objectives Biomechanical testing of bone. Case study on axial testing of bovine cortical bone on MTS Mechanical properties of bone and their use

In-class Exercise Independently address the assigned question (10 minutes). Form group of four, present and discuss each question to identify: –Hypothesis for experimental investigation –Nature of test required to test the hypothesis –Design of test specimen –Outline of experiment and data analyses

Biomechanical Testing of Cortical Bone Hypotheses Based on comparisons of fracture surfaces: 1.Bone is weaker in tension than in shear 2:Bone is stronger in tension than in shear but Tensile yield stress < 2(Yield stress in shear) 3: Bone is stronger in compression than in tension 4: Bone is stronger in compression than in shear 5:Compressive yield stress > 2(Yield stress in shear)

Biomechanical Testing of Cortical Bone Nature of test Monotonic tests to determine yield and ultimate strength under tension, compression and torsion. Properties vary with the rate at which specimens are tested – fixed rate Rate should be similar to in vivo rates

Biomechanical Testing of Cortical Bone Design of test specimen Testing of whole bone –both material and structural properties –Calculation of stress and strain difficult if not impossible Testing of specimens machined from whole bone with standard geometry: –Material properties only –Predictable site of fracture –Easy measurement of stress and strain

Biomechanical Testing of Cortical Bone Design of test specimen 20 Stress = Force/ [  *(0.003^2)/4] Strain = (  L/20)  L- measured via an extensometer

Preparation of test specimen

Biomechanical Testing of Cortical Bone Experimental set-up & data analyses Link to JEC 7104: Orthopaedic Biomechanics Laboratory

Biomechanical Testing of Cortical Bone Experimental set-up & data analyses

Home Work Exercise Using the data file generated from the in- class experiment, calculate: Elastic Modulus Yield stress and strain Ultimate stress and strain