Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

should be taken into account for a realistic determination of the compliance of the MMB
specimens. To consider the effect of test rig deformations, the compliance of the test rig was
determined by use of a thick stiff steel beam of a thickness of 10 mm, width of 25 mm and length
of 250 mm. To determine the compliance of the test rig, denoted as Crig in Equation (5.2), the
compliance of the steel specimen, Csteel, was subtracted from the measured total compliance,
Cmeasured.
C C C
( 5.2)
rig
measured
steel
The compliance of the steel specimen is calculated as
C
steel
cL 2
2L
( 5.3)
3
E b t
st
s
where bs is the width of the steel specimen, c is the lever arm distance, t is the thickness of the
steel specimen, L is the span distance and Est is Young’s modulus of the steel specimen. Finally,
the compliance of the MMB specimens is determined as
C C C
( 5.4)
MMB
Exp
rig
The MMB rig with the steel specimen was loaded in displacement control with 1 mm/min
loading rate up to 100N for the different lever arm distances (c). The results of the compliance
calibration are presented in Figure 5.23. It appears that the compliance of the test rig increases in
a nearly linear fashion with increasing c values.
Compliance of the test rig (m/N)
0.8
0.6
0.4
0.2
0 20 40
c (mm)
60 80
5.23: Compliance of the MMB test rig as a function of lever arm distances, c.
To have an initial crack location for the MMB specimens similar to the initial crack location in
the STT specimens, and to penetrate the resin blob at the crack tip, pre-cracking was conducted
on the MMB specimens. A pre-cracking method proposed by Quispitupa et al. (2011) was used.
The pre-cracking was conducted on a variant of a double cantilever beam configuration as shown
in Figure 5.24. The specimen is clamped between two steel 20 mm thick blocks. A steel block is
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