Abstract: Corrosion is the major cause of structural degradation in industrial plant and structures;
the consequences of not identifying its presence and status can be severe, leading to a myriad of
methods for its evaluation and monitoring. Amongst these there are a large number based on
acoustic methods, and this paper concentrates on three variations involving passive monitoring with
the aim of summarizing their usual area of applications and limitations. Passive monitoring involves
listening to the process of corrosion itself, which usually causes acoustic emission as a result of the
fracture and de-bonding of expansive corrosion products, localised yielding, or micro-crack
formation. This method is applied to reinforced concrete structures, storage tank floors, and process
plant whilst in service.
Abstract: This paper discusses the mechanism of chloride SCC of sensitized and non-sensitized
Type-304 stainless steel based on the data obtained by simultaneous monitoring of AE and corrosion
potential fluctuation (CPF). The steel produced transgranular SCC via corrosion pits filled with
corrosion product (chromium oxy-hydroxides) in 35 mass % MgCl2 solution. Both the pitting
corrosion and transgranular SCC did not produce primary AEs due to anodic dissolution, while they
generated rapid drop (RD) type CPF. We, however, detected the secondary AEs from hydrogen gas
evolution and fracture of corrosion products. Hydrogen gas was found to produce AE with single
frequency component, while the fracture of corrosion products produced AEs with broad frequency
components. The sensitized steel produced primary AEs due to the falling-off of grains as well as the
secondary AEs. Microscopic progression of SCC was consistently interpreted by the timing and
time-lag of AEs and CPFs.
Abstract: Eight composite plates 400x410x2.15mm were fabricated from carbon/epoxy in
((0,90)4)s lay-up. To ensure there was no damage in the plates prior to the impact investigations the
plates were C-scanned. A drop test rig was used to apply a low velocity impact to the undamaged
plates. A rebound mechanism was employed to prevent secondary impacts.
AE sensors were selected for frequency and size due to the limited space on the test rig. Super
glue was used both as a couplant and also to secure the sensors in position. During the impact wave
streaming, time driven data and hit driven data were used to record the impact simultaneously. One
test was conducted on each sample with two impacts completed at 5J, 6J, 8J and 10J (total of 8
samples). The impacts were designed to allow only slight visible impact damage to be formed.
After completion of the impact investigation the plates were C-scanned to determine the area of
debonded material. Analysis of the data showed the complete record of the impact event from the
wave streaming, while the hit driven and time driven absolute energy data provided increasing
correlations with the area of composite damaged.
Abstract: The presence of impact damage in a carbon fibre composite can reduce its capacity to
support an in-plane load, which can lead to an unexpected or premature failure. This paper reports
on an investigation into two slender carbon/fibre epoxy panels, one un-damaged and one with an
artificial delamination introduced using an embedded section of PTFE. The reported tests form part
of a larger series of investigations using differing sizes of artificial delamination and real impact
damage. An investigation of wave velocity propagation at varying angles to the composite lay up
was completed to assist in source location. The specimens were loaded under, uniaxial in-plane
loading and monitored using four resonant acoustic emission sensors. A full field optical
measurement system was used to measure the global displacement of the specimens. Analysis of
AE waveforms and AE hit rate were used to assess the buckling of the panel. The results compared
favourably with the optical measurement results.
Abstract: AE studies were performed considering pressure cylinders of design1 Type II – metallic
liner with hoop composite wrapping, Type III – metallic load sharing liner with full composite
wrapping and Type IV – all-composite cylinder. The AE technique has to be improved so far that
for different design types of cylinders standard AE equipment can be used in an easy and
practicable way under normal conditions of production and service. The paper presents our 8 years
of experience in this application area using conventional AE measuring technique. Potentials,
requirements and limits for detection of manufacturing faults and in-service damages of highpressure
composite cylinders are discussed.
1Cylinder types classification in accordance with ECE R 110 / ISO 11439
Abstract: Some initial studies for an AE characterisation of damage in composites are presented in
this paper. A PAC AE PCI-2 based system and four PAC WD AE broadband sensors are used.
Pencil lead breaks (PLB) were used to introduce a source of elastic waves. An initial validation of
the system based on PLB on an aluminium plate showed that there was a large difference in
sensitivity of the four nominally identical sensors. It is shown that the AE parameters are so
strongly related to the sensitivity of the sensors that they tend to describe the AE system more than
the actual sources. To characterise damage in composite materials alternative AE parameters are
required that are not dependent on the sensitivity of the sensors. In the paper, it is shown that the
frequency spectra of the sources have relatively little variability with respect to the sensor. A
frequency-based approach that examines the spectrum of each source is proposed in the paper. The
procedure is demonstrated using PLBs on a CFRP plate and it is demonstrated that the approach can
indicate the position of the source in relation to orientation of the fibres and the plate edge.
Abstract: An AE measurement system that uses a laser interferometer has been developed to
evaluate microfractures at elevated temperatures in various materials. This technique has the
advantage that it can estimate the temperature where microfractures were generated. The results give
useful information to control process conditions. AE during sintering ceramics and thermal spying of
ceramic powder on metal substrates were successfully detected by this laser AE measurement system.
Effect of process conditions on damage process was discussed from the detected AE behaviour
during in-process monitoring.
Abstract: This research aims to characterise and quantify the acoustic emission (AE) generated
during the high velocity oxy-fuel (HVOF) thermal spraying process, recorded using piezoelectric
AE sensors. The HVOF process is very complex involving high temperature turbulent flow through
a nozzle with entrained particles, the projection of these particles, and their interaction with the
target surface. Process parameters such as gun speed, oxy-fuel pressure and powder specification
affect various characteristics of the coating, including thermal residual stresses; the lamellar
microstructure and the topology and geometry of pores, all formed when the fused powder hits the
surface, forming “splats”. It is widely acknowledged in the thermal spray industry that existing
quality control techniques and testing techniques need to be improved. New techniques which help
to understand the effects of coating process parameters on the characteristics of the coating are
therefore of value, and it was anticipated that recording the AE produced when the fused particles
contact the surface would aid this understanding. As a first stage, we demonstrated here that AE
associated with particle impact can, in fact, be discerned in the face of the considerable airborne and
In order to do this, a new test method using a masking sheet with slits of varying size was
developed. Thermal spraying was carried out for a range of spray gun speeds and process
parameters. The AE was measured using a broad band AE sensor positioned on the back of the
sample as the spot was traversed across it. The results show that the amplitude and energy of the
AE signals is related to the spray gun speed, powder used and the oxy-fuel pressure. Using a simple
geometrical model for particle impact, the measured AE was found to vary with the energy and
number of particles impacting on the sample in a predictable way.
Abstract: The paper summarizes the experiences acquired from on-line acoustic emission
monitoring (herafter AE) of heavy castings during their manufacturing (solidification and following
cooling in the mould). They are usually monitored elastic waves generated above all by stress
changes in the solid state. In order to exactly determine plastic-elastic transition state the
investigation was focused on raising the sensitivity of detection. The suitable experimental
technique is discussed in the first part of this article. The main problem of the measurement by high
temperatures was solved by using waveguides. It is very important in this case to select useful
signal sources from mechanical and electromagnetical disturbances. Some laboratory experiments
were done for studying the signal origin in the first state of solidification.
The results from on-line monitoring of two types cast rolls during manufacturing were
compared. Each type of casting has its typical AE histogram. For the quality evaluation ( in our
case) is significant the time period of approximate 5 days after pouring . The time delayed stress
induced cracking generates high level AE signal in this time period and the presence of such signal
indicates defective product. The study of high temperature tensile tests, structural phase
transformation and solidification processes using AE is very important for analysis of AE sources.
The use of the laboratory results for the AE source analysis on real products will be subject to