L05_Stress%20and%20Strain-08

L05_Stress%20and%20Strain-08 - EAS 209-Spring 2008...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 1 Lecture 05-stress and strain Lecture 5: Chapter 2 Stress and Strain under Axial Loading Design of machines and structures that are safe and function properly requires an understanding of the mechanical behavior of the materials being used. These properties of different materials are ordinarily measured in the laboratory. The most common test is the uniaxial tension test. Of interest is the stress-strain relationship. Recall Stress: A P = σ , Strain: L δ ε= Tests are conducted in accordance with standard protocols. In the U.S. one of the major standards organizations is the American Society of Testing and Materials e.g. ASTM E8-04: Standard Test Methods for Tension Testing of Metallic Materials. EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 2 Lecture 05-stress and strain Uniaxial Tension Test Apply a force P Measure the elongation δ with an extensometer 2 nd dial gage often measures change in diameter From P and δ plot the stress-strain curve 0 A P = 0 L ε = Standard coupon D=0.505 in L (gage length) = 2.0 in The elongation is measured over the gage length
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 3 Lecture 05-stress and strain Typical Stress-Strain for Low Carbon Steel Elastic Region (OB) Stress is proportional to strain up to the proportional limit, P L . Hooke’s Law ε σ = E For steel, E=29x10 6 psi (200 GPa) In the elastic region strains are recoverable if the load is removed – no residual deformation. Between P L and the yield stress, σ y , the material is still elastic, but Hooke’s law no longer applies (non-linear elastic). E is Young’s Modulus or Modulus of Elasticity NOT TO SCALE Ductile Behavior EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 4 Lecture 05-stress and strain Plastic or Yielding Region (BC) Mild steel has a well defined yield strength σ y =30-50 ksi (210-350 MPa) In this region the material deforms plastically – permanent deformation. The bar will not return to its original shape after the load is removed. Large deformation with little or no increase
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

L05_Stress%20and%20Strain-08 - EAS 209-Spring 2008...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online