Lamb wave ultrasonic evaluation of welded AA2024 specimens at tensile static and fatigue testing

The paper deals with the investigation of Lamb waves ultrasonic testing technique applied for evaluation of different stress-strain and damaged state of aluminum specimens at static and fatigue loading in order to develop a Structural Health Monitoring (SHM) approach. The experimental results of tensile testing of AA2024T3 specimens with welded joints are presented. Piezoelectric transducers used as actuators and sensors were adhesively bonded to the specimen's surface using two component epoxy. The set of static and cyclic tensile tests with two frequencies of acoustic testing (50 kHz and 335 kHz) were performed. The recorded signals were processed to calculate the maximum envelope in order to evaluate the changes of the stress-strain state of the specimen and its microstructure during static tension. The registered data are analyzed and discussed in terms of signal attenuation due to the formation of fatigue defects during cyclic loading. Understanding the relations between acoustic signal features and fatigue damages will provide us the ability to determine the damage state of the structure and its residual lifetime in order to design a robust SHM system

Mechanical state assessment using lamb wave technique in static tensile tests

The paper deals with the investigation of Lamb wave ultrasonic technique for damage (or mechanical state) evaluation of AA7068T3 specimens in the course of tensile testing. Two piezoelectric transducers (PZT), one of which is used as an actuator and the other as sensor, were adhesively bonded on the specimen surface using epoxy. Two frequencies of testing signals (60 kHz and 350 kHz) were used. The set of static tensile tests were performed. The recorded signals were processed to calculate the informative parameters in order to evaluate the changes in stress-strain state of the specimens and their microstructure

Application of a Lamb waves based technique for structural health monitoring of GFRP undercyclic loading

A Lamb wave based ultrasonic technique as well as optical image characterization was utilized to estimate a current mechanical state of glass fiber reinforced polymers (GFRP) under cyclic tension. The ultrasonic acoustic method was applied in a 'pitch-catch' mode using piezoelectric transducers adhesively bonded onto a specimen surface. Numerical evaluation of acoustic data was performed by calculating two informative parameters: maximum of amplitude of the received signal and variance of signal envelopes. Optical images were registered and then analysed by calculating Shannon entropy that makes it possible to characterize changing of GFRP specimen translucency. The obtained results were treated in order to find out the relation between the current mechanical state of a specimen and informative parameter values being computed from the acoustic and optical signals

In situ estimation of fatigue crack parameters by digital image correlation under cyclic loading with single overload

The paper represents the investigation of crack propagation in aluminium alloy AA2024 in a case of constant cyclic loading with single overload. The parameters of the process were evaluated by means of optical and noncontact digital image correlation technique which allows precise in situ measurements and provides local strain data. There have been analysed strain fields, local strains at the crack tip and crack closure level in order to reveal the effect of overload on crack growth parameters. Results are consistent with published data and developed mathematical models - the highest impact is emerged when crack extended into overload plastic zone by 30%

Deformation Behavior under Static and Cyclic Tension of Polymer Grafts without and after Modification by RGD Peptides

The structure, mechanical properties, and deformation behavior under static and cyclic tension of biofunctionalized biodegradable vascular grafts based on polyhydroxybutyrate/valerate and polycaprolactone were studied. It is shown that the modification gives rise to an almost twofold decrease of the elongation at break as well as the ultimate strength. It is shown that under cyclic loading the modification of grafts results in decreasing cyclic durability by more than twice. In doing so, the level of deforming stress decreases to a much lesser extent and is practically inferior to that for unmodified material. The analysis of principal strain [epsilon]1 and [epsilon]2 component distribution patterns in grafts of both types is carried out while the reason for the observed changes is discussed