14 research outputs found
Impact damage detection in composite plates using deflectometry and the Virtual Fields Method
No full textThis paper presents a new method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a “signature” from the measured surface slopes. Firstly, this method is applied to plate specimens using numerical and experimental data. Secondly, damage indicator based on a new application of the virtual fields method to compute local apparent gaps in equilibrium is presented and used to process the measurements on plates. It is shown that the damage indicator is very sensitive, allowing detection of damage that is difficult to identify directly from the strain maps
Damage detection in composite materials using full-field slope measurements
No full textThis paper presents a method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a ‘‘signature’’ in the form of surface slopes. The first part of the paper presents the experimental procedure: material, lay-up and sample types, then the set-up and data extraction are detailed followed by the finite element (FE) models. Finally the results are presented and commented
Time-resolved full-field imaging of ultrasonic Lamb waves using deflectometry
No full textThis pioneering experimental work is a proof of concept in which ultrasonic flexural waves have been imaged in a spatially and temporally resolved manner. Thin vibrating plates made of mirror glass and carbon/epoxy composite have been used in the experiments. Results obtained via a standard approach (scanning laser Doppler vibrometry) and the novel methodology based on deflectometry have been compared with a multi-physics finite element simulation. There is a very good correlation between the two experimental techniques. The numerical model provides insight into the experiments, but differs in its detailed structure due to uncertainties over material properties. The extreme slope resolution of deflectometry allows the measurement of peak-to-peak deflections of a few tens of nanometres in one shot. The use of an ultra-high speed camera allows for both space and time resolved measurements of Lamb waves which, to the best knowledge of the authors, has never been reported before. The limitations of the technique arise from the need for a flat specularly reflective surface. However, coating is possible for non-reflective materials and extension to moderately curved surfaces is possible in the future
Mechanical characterization of open cell aluminium foams reinforced by nickel electro-deposition
No full textLow cost infrared thermography for automated crack monitoring in fatigue testing
No full textThe potential of using infrared thermography in the assessment of crack-tip parameters is described. The use of microbolometers is studied specifically to establish their suitability for use in thermoelastic stress analysis (TSA) for establishing the crack-tip parameters and for automatically monitoring crack growth using temperature measurement. To compare the behaviour of the two types of infrared cameras a camera model is devised, which is used to predict the thermoelastic response. A new automatic crack growth monitoring approach is developed based on the temperature measurement from the raw thermal data collected using the microbolometer. The thermoelastic response model and the crack monitoring procedure are demonstrated on 316 L stainless steel single edge notch tension (SENT) specimens. Cracks were established in the specimens, grown and monitored using both types of infrared detector. The procedure is validated using measurements from the photon detector and it is shown that accurate stress intensity factors (SIFs) can be obtained from growing cracks using directly the live readings from the microbolometer. The procedure provides a new means for non-contact measurements in fatigue testing, establishing crack growth rate and the SIFs with the potential for actuator control.</p
Correlation between full-field measurements and numerical simulation results for multiple delamination composite specimens in bending
No full textThis paper studies the effect of delaminations on strain maps for a simple cantilever beam. The aim is to build an experimental set-up which allows detecting very slight modifications in the strain maps. The case studied is a single delamination on the mid-plane. The measurement method is the deflectometry technique which enables direct slope measurements on a reflective specimen. The comparison with finite element models clearly indicated that the surface strains bear the information of the extent of the delamination. The second step is to use these surface strains to identify a stiffness reduction map for real impact damages.</jats:p
Detecting barely-visible impact damage in composites using full-field slope measurements
No full text
Influence of ripening on pHstat leaching of heavy metals from dredged sediments
No full textThe influence of oxidation and ripening on the kinetics of heavy metal release from anoxic sediments was investigated by means of porewater analysis and pHstat leaching tests. During simulated land disposal of an anoxic river sediment, a considerable heavy metal (Cd, Zn and Ni) release into the porewater was observed after 25 days of exposure of the sediment to the air. The release kinetics of Cd and Zn during pHstat leaching indicated that their release was related to the oxidation of Cd- and Zn-sulfides. It was not completely clear whether the release of Ni was due to the oxidation of Ni-sulfides or to the introduction of H+(generated by the oxidation of sulfides or introduced by titration). The release of Cu seemed to be explained by the oxidation of both Fe-sulfides and Cu-sulfides. As such, pHstat experiments provided an indirect way to assess the mineralogy of the anoxic sediment. During ripening of the sediment, the release rate of Zn and Cd in pHstat leaching tests increased. For Ni, however, a similar release pattern was observed in the anoxic sediment and in the ripened sediments. Two weeks drying at 100 °C resulted in an increase in the leachability of Cu. Nevertheless, at pH 4 and 6, the thermally treated sediment displayed a slower leaching of Cd and Zn than the ripened sediment. Although thermal treatment is often used to simulate ageing in soils, it cannot be used to simulate ripening of anoxic sedimentsstatus: Publishe
