MEKANIKA MATERIAL (BAHAN) Jenis pembebanan pada material Jenis tegangan (stress) Perhitungan kekuatan material untuk menentukan dimensi dan pemilihan bahan berdasarkan jenis pembebanan yang terjadi
Terminology for Mechanical Properties Stress - Force or load per unit area of cross-section over which the force or load is acting. Strain - Elongation change in dimension per unit length. Young’s modulus - The slope of the linear part of the stress-strain curve in the elastic region, same as modulus of elasticity. Shear modulus (G) - The slope of the linear part of the shear stress-shear strain curve.
Engineering Stress Stress has units: N/m2 (or lb/in2 ) Tegangan Normal (): intensitas gaya yang bekerja tegak lurus bidang irisan contoh: Tensile stress, () Tegangan geser (): intensitas gaya yang bekerja sejajar bidang irisan Contoh : Shear stress, (): Stress has units: N/m2 (or lb/in2 )
Modes of loading and states of stress
Modes of loading and states of stress
Modes of loading and states of stress
PEMBEBANAN PADA BEJANA TEKAN
PEMBEBANAN PADA BEJANA TEKAN
Tegangan Hoop pada bejana tekan
Gaya Hoop pada bejana tekan Berdasarkan gambar d akan diuraikan gaya-gaya yg berlaku
Pure Tension Pure Compression stress strain Elastic response Pure Shear stress strain Elastic response Pure Torsional Shear 26
Mekanika bahan konsep stress
Hooke’s law for extension: σ = E Hooke’s law for shear: = G
1 Pa = 145.04×10−6 psi
Hooke’s law for extension: σ = E Hooke’s law for shear: = G
Common States of Stress • Simple tension: cable Ski lift (photo courtesy P.M. Anderson) • Simple shear: drive shaft Note: t = M/AcR here. 34
(c)2003 Brooks/Cole, a division of Thomson Learning, Inc (c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. gauge length Figure. A unidirectional force is applied to a specimen in the tensile test by means of the moveable crosshead. The cross-head movement can be performed using screws or a hydraulic mechanism
Properties Obtained from the Tensile Test Elastic limit Tensile strength, Necking Hooke’s law Poisson’s ratio Modulus of resilience (Er) Tensile toughness Ductility
Test Specimen Standard
Figure. The stress-strain curve for an aluminum alloy (c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure. The stress-strain curve for an aluminum alloy
(c)2003 Brooks/Cole, a division of Thomson Learning, Inc (c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure. (a) Determining the 0.2% offset yield strength in gray cast ion, and (b) upper and lower yield point behavior in a low-carbon steel
cup-and-cone fracture in Al Figure. Localized deformation of a ductile material during a tensile test produces a necked region brittle fracture in mild steel 40
(Ultimate) Tensile Strength, σTS • Maximum possible engineering stress in tension. y strain Typical response of a metal F = fracture or ultimate strength Neck – acts as stress concentrator engineering TS stress engineering strain • Metals: occurs when necking starts. • Ceramics: occurs when crack propagation starts. • Polymers: occurs when polymer backbones are aligned and about to break. 41
Deformation Process During Test
cup-and-cone fracture in Al (c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. cup-and-cone fracture in Al Figure. Localized deformation of a ductile material during a tensile test produces a necked region brittle fracture in mild steel 46
EULER CRITERIA
Modes of loading and states of stress
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