Abstract: Dual phase steels (DPS)s have a microstructure
consisting of a hard second phase called Martensite in the soft Ferrite
matrix. In recent years, there has been interest in dual-phase steels,
because the application of these materials has made significant usage;
particularly in the automotive sector Composite microstructure of
(DPS)s exhibit interesting characteristic mechanical properties such
as continuous yielding, low yield stress to tensile strength
ratios(YS/UTS), and relatively high formability; which offer
advantages compared with conventional high strength low alloy
steels(HSLAS). The research dealt with the characterization of
damage in (DPS)s. In this study by review the mechanisms of failure
due to volume fraction of martensite second phase; a new method is
introduced to identifying the mechanisms of failure in the various
phases of these types of steels. In this method the acoustic emission
(AE) technique was used to detect damage progression. These failure
mechanisms consist of Ferrite-Martensite interface decohesion and/or
martensite phase fracture. For this aim, dual phase steels with
different volume fraction of martensite second phase has provided by
various heat treatment methods on a low carbon steel (0.1% C), and
then AE monitoring is used during tensile test of these DPSs. From
AE measurements and an energy ratio curve elaborated from the
value of AE energy (it was obtained as the ratio between the strain
energy to the acoustic energy), that allows detecting important
events, corresponding to the sudden drops. These AE signals events
associated with various failure mechanisms are classified for ferrite
and (DPS)s with various amount of Vm and different martensite
morphology. It is found that AE energy increase with increasing Vm.
This increasing of AE energy is because of more contribution of
martensite fracture in the failure of samples with higher Vm. Final
results show a good relationship between the AE signals and the
mechanisms of failure.
Abstract: Repairing of the cracks by fiber metal laminates
(FMLs) was first done by some aeronautical laboratories in early
1970s. In this study, experimental investigations were done on the
effect of repairing the center-cracked aluminum plates using the FML
patches. The repairing processes were conducted to characterize the
response of the repaired structures to tensile tests. The composite
patches were made of one aluminum layer and two woven glassepoxy
composite layers. Three different crack lengths in three crack
angles and different patch lay-ups were examined. It was observed
for the lengthen cracks, the effect of increasing the crack angle on
ultimate tensile load in the structure was increase. It was indicated
that the situation of metal layer in the FML patches had an important
effect on the tensile response of the tested specimens. It was found
when the aluminum layer is farther, the ultimate tensile load has the
highest amount.