1. KONSTRUKSI MESIN (3 SKS)
MODUL 11
TEGANGAN DAN REGANGAN
DOSEN: JAMIATUL AKMAL, S.T., M.T.
PROGRAM KULIAH SABTU MINGGU
JURUSAN TEKNIK MESIN
FAKULTAS TEKNOLOGI INDUSTRI
UNIVERSITAS MERCU BUANA
JAKARTA
2007
Tegangan dan Regangan
From statics, one can only determine the internal member forces and/or moments
in structural members subject to some loading. However the behaviour of a

2. Plotting the variation of axial force
against the elongation results in the
diagram in Figure 2.1 where there
are three curves corresponding to
the three bars. We do not get a
unique plot. If we were to plot the
variation of the average intensity
of the force defined by force per

3. AA
P dF .dA
If the stress is uniform, then P =
A or
= P/A
Otherwise, we can only say that the average stress
= P/A
When referring to normal stresses in more than one direction, a subscript may be
used to indicate the direction on which the stress is acting. For example, x
denotes the normal stress in x-direction.
Note that the normal stress distribution in an axially loaded member may be taken
as being uniform, except in the immediate vicinity of the points of application of
loads, provided the loading is centric (applied through the centroid of the cross
section of the member). If the loading were eccentric, the resulting stress
distribution would be non-uniform and would cause bending. In the immediate
vicinity of concentrated loads, and near points where the cross section of the
member changes abruptly, there will develop some stress concentration, which
may be taken into account using stress concentration factors.
Shearing Stress (Shear Stress):
Shear stress is defined as the intensity of shearing force acting on a plane at a
point. The Greek letter tau ( ) is used to denote shear stress.
Examples: Shear stress may occur as a result of torsional loading, transverse
loading and is also induced in connections (rivets, bolts etc.). Axial loading also
causes shearing stress in oblique planes.
Sign Convention & Notation:
It is common practice to indicate the
direction of the shear stress using two
subscripts. For example,
xy indicates the
stress acting in the y direction on (x-plane) a
perpendicular to the x-axis. The sign
convention that is used in most texts is
shown in the diagram. Here the stresses are
shown to act in the positive co-ordinate directions on positive faces, and negative
co-ordinate directions on negative faces..