Class-Notes-3-4-Intro-Strength-Mat - Introduction to...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Introduction to Strength of materials: (Chapter-2) Class #3, #4 – September 20, 27 Introduction to Stress and Strain, and mechanics of deformable bodies Stress: Load/Area or Force/Area [F/L.L] [kips/square inch] Where F=Force (pound force) and L=Length (inches or feet for SI units) Strain: Change in length over original length of the member under tensile or compressive load. As we load the material, the material will extend if the extension we all delta L, L, or change in length, then the change in length divided by the original length will give us the strain in the material ε = L/L [Unit of Length/Unit of Length] and therefore it is a dimensionless quantity. To establish a relationship between stress and strain, we can perform tests on a given specimen, one such test is the tensile test, where the specimen is loaded in tension in a machine (Tensile Test Machine) and the stress and strain are recorded. The graph looks like the one in figure bellow: (Note: Tests including but not limited to tensile tests on crystals of materials have also been performed using other mechanical means which we will cover later) σ ε σ ε σ ε Figure-1: Relation between Stress and Strain The slope of the stress strain Curve is termed the Modulus of Elasticity. Or Young’s Modulus. And the relationship is called Hooke’s Law as he was the first person to observe that there is a linear relationship between stress and elongation of a bar in tension. From the graph it can be observed that the stronger the material the greater the slope, so in Figure- 1 wee see that steel is the strongest material Es, then Aluminum, (E AL ), and then Ec Concrete. Looking at a typical stress strain curve, when the specimen is loaded, it will deform and elongate as shown below in a linear fashion with a slope E up to the proportional limit. At this point the material if loaded further will start to yield. If unloaded the specimen will return to its origin O. (Approximately, with a 0.2% offset) After the yield the material is in plastic region and if unloaded the material will not return to its original length and will have what is called a permanent deformation or permanent set. Passed the elastic range in Figure-3, each time we reload then the material becomes stronger but its elastic limit/point decreases if loaded to the elastic limit and becomes less ductile.
Image of page 1

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

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern