SMU 2113 ENGINEERING SCIENCE. PART 1 Introduction to Mechanics of Materials and Structures

Transcription

1 SMU 2113 ENGINEERING SCIENCE PART 1 Introduction to Mechanics of Materials and Structures These slides are designed based on the content of these reference textbooks.

2 OBJECTIVES To introduce basic principles of the mechanics of materials and structures. To illustrate the applications of mechanics of materials for structural members subjected to simple loading conditions. At the end of PART 1, students should be able to: - calculate deformation, strains and stresses of a structural member subjected to simple loading, namely axial, direct shear, torsion and bending. - identify the various mechanical properties of common engineering materials. - analyze elastic deflection of a beam.

3 Mechanics of Materials A branch of mechanics that studies the relationships between external loads applied to a deformable body and the intensity of internal forces acting within the body.

4 SCOPE Stress Strain Equilibrium of forces Mechanical properties of materials Stress-strain diagram Axial force Torsion Bending Numerous examples/ applications

5 Typical Engineering Structures Applications involving combined loading What types of materials are these structures made of?

6 Types of loading on structures LOAD SYMBOL UNITS (Metrics) UNITS (Engineering) Direct Force F, P N lb f Shear Force V, Q N lb f Torsion T Nm lb f -ft Bending Moment M Nm lb f -ft Fluid Pressure p Nm -2 psi Temperature Difference T o C o F

7 B DESIGN PROPERTIES OF MATERIALS Engineering materials: metals and nonmetals Tension test The stress-strain diagram Mechanical properties Elastic modulus, E Yield strength, Y Tensile strength, UTS Ductility, f Physical properties Coefficient of thermal expansion, CTE,

8 Periodic table of elements

9 Classification of solid materials Metals - normally, combinations of metallic elements - elements: aluminum (Al), copper (Cu), tin (Sn), silver (Ag) - alloys: steels, solders (Sn-37Pb, Sn-4Al-0.5Cu) - intermetallics: Ti-48Al Ceramics - compounds between metallic and nonmetallic elements - oxides (SiO 2 ), nitrides (Si 3 N 4 ) and carbides (WC) - clay cement and glass - hard but brittle Polymers - Many are organic compounds, based on C, H and other nonmetallic elements - low density; high strength-to-weight ratio Other groups Composites, Semiconductors and Biomaterials

10 Components on materials science and engineering, and their interrelationship Performance

11 Strength of materials The strength of a material depends on its ability to sustain a load without undue deformation. This inherent property is determined by experiment. One of the most important test is the tension test.

12 Engineering Stress and strain P Engineering stress, Engineering strain, = P A o = L o = L - L o L o Percent elongation = L f - L o L o X100 % L o L Percent reduction of area = A 0 - A f X100 % A 0 P P applied force A o original cross-sectional area L o original gage length L instantaneous length L f length at fracture

13 Tension test machine Load cell Crosshead Extensometer Specimen grips Specimen Data acquisition system

14 Stress-strain diagram (1)

15 Stress-strain diagram (2) UTS Fractured Necking Tensile failure in ductile material is associated with large plastic deformation. Y Fractured Total = el + pl Elastic Plastic f

16 Stress-strain diagram for ductile material (mild steel)

17 Yielding and yield strength

18 Stress-strain diagram for ductile material (aluminum) Offset yield strength

19 Example Problem

20 Solution to example problem (1)

21 Solution to example problem (1)

22 Stress-strain diagram for ductile material (mild steel)

23 Stress-strain diagram for stainless steel Properties Values 600 y0.2% (MPa) 429 Tegasan ( MPa) Ujikaji A Ujikaji B u (MPa) 604 E (GPa ) 208 n K ( MPa ) Terikan Stress-strain curves for Type 316 SS

24 Mechanical properties of some materials

25 Coefficient of thermal expansion (CTE) A change in temperature, T can cause a material to change its dimension. This deformation, T (linear expansion or contraction) of a member having a length, L can be calculated as T = T L where is a physical property called the linear coefficient of thermal expansion (CTE) If thermal displacements of a structural member is constrained by the supports, then thermal stresses must be considered in design

26 Thermal properties of materials (1)

27 Thermal properties of materials (1)