The fatigue of dough moulding compound and the strength of bolted joints
The use of dough moulding compound (DMC) as a structura~
material will be feasible as more information on mechanlcal
properties becomes available. In this investigation, room
temperature tensile and fatigue properties were determined
prior to the testing and evaluation of simple joints in
The DMC was supplied in the form of compression moulded
sheets. Tensile tests were conducted to British Standards
specification to obtain the mechanical properties and to
identify possible sources of variability in properties.
Differences in tensile strength due to sheet-to-sheet
variability and specimen orientation within a sheet were
significant but there was no significant variation due to
the cross-head speed over the range O.05mm/min to 300mm/min.
Tensile fatigue tests were conducted to British Standards
specification. The scatter of fatigue lives was found to be
greater than that for other reinforced plastics, but was
adequately described by both the Log-Normal and Weibull
In tensile and fatigue tests on larger specimens there was
no size effect on tensile strength, but the fatigue strength
at a given life and probability of failure was reduced
,slightly. When specimens contained bolt holes, the tensile
strength decreased marginally, but the fatigue strength
was not affected.
Transverse compressive stresses due to a bolt load had
little effect on the fatigue behaviour and changes in the
cyclic-or static stress did not significantly alter the
bolt load relaxation. Cyclic stress was found to cause
greater bolt load relaxation than the corresponding mean stress.
In tensile and fatigue tests on single shear lap joints,
benditig wa~ the main cause of failure and the joint
efficiency was low, 43% in tension and 51% in fatigue.
By loading the specimens through the bolts at one end,
bending was eliminated and the joint efficiency increased
to 62% in tension and to 78% in fatigue