kuliah 3_2 dpm

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


Head tube sepeda patah


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.


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


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.



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


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


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 ( )


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


Sign Convention

Figure 2.3 Sign convention used

in bending. (a) y coordinate

upward; (b) y coordinate

downward.



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.


Supports and Reactions

Table 2.1: Four types of support with their

corresponding reactions.

text reference: Table 2.1, page 35


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


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


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.


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.)


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.


Beam Supports

Figure 2.8 Three types of beam support. (a) Simply supported; (b) cantilevered; (c)

overhanging.



Simply Supported Bar

Figure 2.9 Simply supported bar with (a) midlength load and reactions; (b) free-body

diagram for 0


Singularity Functions (Part 1)

Table 2.2 Six singularity and load intensity functions with corresponding graphs and

expressions.


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


Shear and Moment Diagrams

Figure 2.10 (a) Shear and (b) moment diagrams for Example 2.8.



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.



Example 2.10

Figure 2.12 Figures used in Example 2.10. (a) Load assembly drawing; (b) free-body

diagram.



General State of Stress

Figure 2.13 Stress element showing general state of three-dimensional stress with

origin placed in center of element.



2-D State of Stress

Figure 2.14 Stress element showing two-dimensional state of stress. (a) Three

dimensional view; (b) plane view.


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.



Stresses in Oblique Plane

Figure 2.16 Stresses in oblique plane at angle .



Mohrs Circle

Figure 2.17 Mohrs circle

diagram of Eqs. (2.13) and

(2.14).



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.



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.



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.



Stresses on Octahedral Planes

Figure 2.21 Stresses acting on octahedral planes. (a) General state of stress. (b)

normal stress; (c) octahedral shear stress.



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.



Shear Strain

Figure 2.23 Shear strain of cubic element subjected to shear stress. (a) Three

dimensional view; (b) two-dimensional (or plane) view.



Plain Strain

Figure 2.24 Graphical depiction of plane strain element. (a) Normal strain x; (b) normal

strain y; and (c) shear strain xy.



Strain Gage Rosette

Figure 2.25 Strain gage rosette used

in Example 2.17.



Honeycomb Expansion Process

Figure 2.26 Expansion process used in

honeycomb materials. [From Kalpakjian (1991)]



Glue Spreader Case Study

Figure 2.27 Glue spreader case study. (a) Machine; (b) free body diagram; (c) shear

diagram; (d) moment diagram.



Snowmobile with Drive Guard

Figure 2.28 Illustration used in case study. (a) Snowmobile; (b) guard with

instrumentation.



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


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


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

kuliah 3_2 dpm

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