Upload
luthfan-hawari-putranto
View
27
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Basic Engineering Design
Citation preview
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Chapter 2: Load, Stress and Strain
When I am working on a problem, I never think
about beauty. I only think of how to solve the
problem. But when I have finished, if the solution
is not beautiful, I know it is wrong.
Richard Buckminster Fuller
Image: A dragline lifts a large load in a
mining operation.
1998 McGraw-Hill Hamrock, Jacobson, Schmid Text Reference: Figure 1.4, page 21
DESIGN OF MACHINE ELEMENTS
1. Selecting a suitable type of machine element from
consideration of its function (Joinning, Transmission,
etc)
2. Estimating the size of the machine element that is
likely to be satisfactory (standart bolt, material,etc)
3. Evaluating the machine elements performance
against the requirements (horse power, torsion,etc)
4. And then modifying the design and the dimensions
until the performance is wear to whichever optimum
is considered most important
1998 McGraw-Hill Hamrock, Jacobson, Schmid Text Reference: Figure 1.4, page 21
A Machine Element is
Considered to have FAILED
1. When it becomes completely inoperable
2. When it is still operable but is unable to perform
its intended function satisfactorily
3. When serious deterioration has made it unrealiable
or unsafe for continued use, necessitating its
immediate removal from service for repair or
replacement
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Head tube sepeda patah
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Objectives
Design and Analysis of machines and machine elements.
Since machine elements carry loads, it follows that an
analysis of loads esessential in machine element design.
Proper selection of a machine element often is a simple
matter of calculating the stress or deformations expected
in service and then choosing a proper size so that critical
stresses or deformations are not exceeded. The first step
in calculating the stress or deformation of a machine
element is to accurately determine the load.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Critical Section
text reference: Figure 2.1, page 30
To determine when a machine element will fail, the
designer evaluates the stress, strain, and strength at the
critical section
1. Considers the external loads applied to a machine
2. Considers the external loads applied to an element
within the machine
3. Locates the critical section within the machine
element
4. Determines the loading at the critical section
1998 McGraw-Hill Hamrock, Jacobson, Schmid
A Simple Crane
Figure 2.1 A simple crane and
forces acting on it. (a) Assembly
drawing; (b) free-body diagram
of forces acting on the beam.
text reference: Figure 2.1, page 30
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Load Classification
Any applied load can be classified with respect to time in
the following ways :
1. Static load-Load is gradually applied and equilibrium
is reached in a relatively short time. The structure
experiences no dynamic effects
2. Sustained load-Load, such as the weight of a
structure, is constant over a long time
3. Impact load-Load is rapidly applied. An impact load
is usually attributed to an energy imparted to a system
4. Cyclic Load-Load can vary and even reverse itselft in
sign and has a characteristic period with respect to
time
1998 McGraw-Hill Hamrock, Jacobson, Schmid
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Load Classification
The load can also be classified with respect to the area
over which it is applied :
1. Concentrated load-Load is
applied to an area much
smaller than the loaded member,
as presented for nonconformal surfaces
2. Distributed load-Load is spead along the entire area,
such as the weight of a structure, is constant over a
long time
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Load Classification
Load can be further classified with respect to location
and method of application. Also coordinate direction
must be determined before the sign of the loading can
be established :
1. Normal Load ( )
2. Shear load ( )
3. Bending Load ( )
4. Torsion Load ( )
5. Combined Load ( )
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Load Classification
Figure 2.2 Load classified as to location and method of application. (a) Normal,
tensile (b) normal, compressive; (c) shear; (d) bending; (e) torsion; (f) combined
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Sign Convention
Figure 2.3 Sign convention used
in bending. (a) y coordinate
upward; (b) y coordinate
downward.
text reference: Figure 2.3, page 32
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Lever Assembly
Figure 2.4 Lever assembly and results.
(a) Lever assembly; (b) results showning
(1) normal, tensile, (2) shear, (3)
bending, (4) torsion on section B of lever
assembly.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Supports and Reactions
Table 2.1: Four types of support with their
corresponding reactions.
text reference: Table 2.1, page 35
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Static Equilibrium
Equilibrium of a body requires both a balance of
forces, to prevent the body from translating (moving)
along straight or curved path, and a balance of
moments, to prevent the body from rotating
Px = 0 Py = 0 Pz = 0
Mx = 0 My = 0 Mz = 0
Static equilibrium for x-y plane
Px = 0 Py = 0 Mz = 0
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Pindah ke MechanicHandout
Support an Reaction
LOAD dalam merancang komponen harus
ditentukan oleh si Perancang
LOAD memiliki besar, arah dan garis Gaya
LOAD Unitnya kg, N
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Ladder Free Body Diagram
Figure 2.5: Ladder having contact with the house
and the ground while having a painter on the ladder.
Used in Example 2.4. The ladder length is l.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
External Rim Brake and Forces
Figure 2.6 External rim brake and forces acting on it. (a) External rim brake; (b)
external rim brake with forces acting on each part. (Linear dimensions are in
millimeters.)
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Sphere and Forces
Figure 2.7 Sphere and forces acting on it. (a)
Sphere supported with wires from top and a
spring at the bottom; (b) free-body diagram of
forces acting on the sphere. Figure used in
Example 2.6.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Beam Supports
Figure 2.8 Three types of beam support. (a) Simply supported; (b) cantilevered; (c)
overhanging.
text reference: Figure 2.8, page 39
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Simply Supported Bar
Figure 2.9 Simply supported bar with (a) midlength load and reactions; (b) free-body
diagram for 0
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Singularity Functions (Part 1)
Table 2.2 Six singularity and load intensity functions with corresponding graphs and
expressions.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Singularity Functions (Part 2)
Table 2.2 Six singularity and load intensity functions with corresponding graphs and
expressions. text reference: Table 2.2, page 43
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Shear and Moment Diagrams
Figure 2.10 (a) Shear and (b) moment diagrams for Example 2.8.
text reference: Figure 2.10, page 44
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Simply Supported Beam
Figure 2.11 Simply supported beam. (a) Forces acting on beam when P1=8kN, P2=5kN;
w0=4kN/m; l=12m; (b) free-body diagram showing resulting forces; (c) shear and (d)
moment diagrams of Example 2.9.
text reference: Figure 2.11, page 46
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Example 2.10
Figure 2.12 Figures used in Example 2.10. (a) Load assembly drawing; (b) free-body
diagram.
text reference: Figure 2.12, page 48
1998 McGraw-Hill Hamrock, Jacobson, Schmid
General State of Stress
Figure 2.13 Stress element showing general state of three-dimensional stress with
origin placed in center of element.
text reference: Figure 2.13, page 49
1998 McGraw-Hill Hamrock, Jacobson, Schmid
2-D State of Stress
Figure 2.14 Stress element showing two-dimensional state of stress. (a) Three
dimensional view; (b) plane view.
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Equivalent Stresses
Figure 2.15 Illustration of equivalent stresss states; (a) Stress element oriented in the
direction of applied stress. (b) stress element oriented in different (arbitrary)
direction.
text reference: Figure 2.15, page 52
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Stresses in Oblique Plane
Figure 2.16 Stresses in oblique plane at angle .
text reference: Figure 2.16, page 52
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Mohrs Circle
Figure 2.17 Mohrs circle
diagram of Eqs. (2.13) and
(2.14).
text reference: Figure 2.17, page 55
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Results from Example 2.13
Figure 2.18 Results from Example
2.13 (a) Mohrs circle diagram;
(b) stress element for principal normal
stresses shown in x-y coordinates;
(c) stress element for principal stresses
shown in x-y coordinates.
text reference: Figure 2.18, page 57
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Mohrs Circle for Triaxial Stress State
Figure 2.19 Mohrs circle for triaxial stress state. (a) Mohrs circle representation;
(b) principal stresses on two planes.
text reference: Figure 2.19, page 59
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Example 3.5
Figure 2.20 Mohrs circle diagram for
Example 3.5. (a) Triaxial stress state when
1=23.43 ksi, 2=4.57 ksi, and 3=0; (b)
biaxial stress state when 1=30.76 ksi and
2=-2.760 ksi; (c) triaxial stress state when
1=30.76 ksi, 2=0, and 3=-2.76 ksi.
text reference: Figure 2.20, page 60
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Stresses on Octahedral Planes
Figure 2.21 Stresses acting on octahedral planes. (a) General state of stress. (b)
normal stress; (c) octahedral shear stress.
text reference: Figure 2.21, page 61
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Normal Strain
Figure 2.22 Normal strain of cubic element subjected to uniform tension in x
direction. (a) Three dimensional view; (b) two-dimensional (or plane) view.
text reference: Figure 2.21, page 64
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Shear Strain
Figure 2.23 Shear strain of cubic element subjected to shear stress. (a) Three
dimensional view; (b) two-dimensional (or plane) view.
text reference: Figure 2.23, page 65
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Plain Strain
Figure 2.24 Graphical depiction of plane strain element. (a) Normal strain x; (b) normal
strain y; and (c) shear strain xy.
text reference: Figure 2.24, page 66
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Strain Gage Rosette
Figure 2.25 Strain gage rosette used
in Example 2.17.
text reference: Figure 2.25, page 68
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Honeycomb Expansion Process
Figure 2.26 Expansion process used in
honeycomb materials. [From Kalpakjian (1991)]
text reference: Figure 2.26, page 68
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Glue Spreader Case Study
Figure 2.27 Glue spreader case study. (a) Machine; (b) free body diagram; (c) shear
diagram; (d) moment diagram.
text reference: Figure 2.27, page 69
1998 McGraw-Hill Hamrock, Jacobson, Schmid
Snowmobile with Drive Guard
Figure 2.28 Illustration used in case study. (a) Snowmobile; (b) guard with
instrumentation.
text reference: Figure 2.28, page 70
1998 McGraw-Hill Hamrock, Jacobson, Schmid
TUGAS 2
Perkirakan beban yang
diperhitungkan/dipertimbangkan pada disain
alat yang anda pilih di tugas 1 dan berapa
besarnya dan menurut anda gimana cara
memperkirakan besar beban tersebut
1998 McGraw-Hill Hamrock, Jacobson, Schmid
ULANGAN Reaksi Tumpuan
29 September 2011
60
B A
P2 = 1 kN
P3 = 1 kN P1 = 1 kN
1,5 m 1,5 m 1,5 m 1,5 m
1 m
1 m
Hitung Besar Reaksi Tumpuan di A dan B dengan
menggunakan Metode Grafis dan Teoritis
1998 McGraw-Hill Hamrock, Jacobson, Schmid
ULANGAN N,V,M
6 Oktober 2011
Gambar diagram N,V,M dari konstruksi sederhana diatas
1,0 m
2,0 m
1,0 m
2,0 m
45
A B
q1 = 1 N/cm
P = 1 kN
q2 = 2 N/cm