... ACKNOWLEDGEMENT Marnix Surgeon wishes to thank the Flemish IWT for granting him a research fe... more ... ACKNOWLEDGEMENT Marnix Surgeon wishes to thank the Flemish IWT for granting him a research fellowship. REFERENCES ... Dublin, 125–130. 8. Liu, K., Ferguson, SM and Measures, RM 1989. SPIE Vol. 1170 Fibre Optic Smart Structures and Skins II, 205–210. ...
The establishment of reliable correlations between the extend of damage and a sensor response usi... more The establishment of reliable correlations between the extend of damage and a sensor response using automated non destructive testing (structural health monitoring) is the first aim of the present paper. The second and its main aim is the estimation of the efficiency of different approaches of the fatigue crack prediction when scalar parameters are used to represent the signal-response. Investigation of ultrasonic Lamb wave interaction with a fatigue crack has been performed on thin sheets (1mm) of aluminum alloy (2024-Т3). Three parameters of response were selected to compare efficiency and the standard deviation of a predicted fatigue crack was used for comparison. Quite definitely it is possible to conclude, that the proposed technology is capable of providing high stability and necessary accuracy at the continuous integrated SHM of thin-walled aluminum components of aircraft. It is also shown that the accuracy of damage prediction is one of the most significant parameter of SHM efficiency. It can be used as the main criterion at selection of diagnostic parameters for continuous integrated monitoring of structural elements of aircraft.
The acoustic emission (AE) technique is used for investigating the interfacial fracture and damag... more The acoustic emission (AE) technique is used for investigating the interfacial fracture and damage propagation in GFRP-and SRG-strengthened bricks during debonding tests. The bond behavior is investigated through single-lap shear bond tests and the fracture progress during the tests is recorded by means of AE sensors. The fracture progress and active debonding mechanisms are characterized in both specimen types with the aim of AE outputs. Moreover, a clear distinction between the AE outputs of specimens with different failure modes, in both SRG-and GFRPstrengthened specimens, is found which allows characterizing the debonding failure mode based on acoustic emission data.
A phenomenon which has been termed ''multilayered Rayleigh modes'' has been presented in previous... more A phenomenon which has been termed ''multilayered Rayleigh modes'' has been presented in previous papers. This study aims to prove experimentally the existence of these waves in anisotropic periodically multilayered media. These modes result from a combination of Floquet waves which propagate in a periodically multilayered medium when all the Floquet waves are inhomogeneous. The experimental verification was done using an acousto-optic technique and a measurement of the reflected field, which was obtained with a hydrophone measurement system, on a carbon/epoxy composite plate. The experimental and calculated dispersion curves of the multilayered Rayleigh modes were then drawn. The coincidence of the curves was found quite good, thus confirming our theory. However, two modes were found by the acousto-optic technique not to fit into the theory. One experimentally detected mode was found to correspond to the Lamb mode of the plate and the other was not experimentally detected by the acousto-optic technique. Measurement of the reflected field for this mode, which was obtained with a hydrophone measurement system, and its comparison with the predicted reflected field make it possible to verify the existence of the mode. The combination of both experiments permit a good coincidence to be found.
The acousto-optic technique presented by Wevers, Devolder, Leroy, and De Meester ͓Appl. Phys. Let... more The acousto-optic technique presented by Wevers, Devolder, Leroy, and De Meester ͓Appl. Phys. Lett. 66, 1466 ͑1995͔͒ was based on the information concerning the phase shift between the incident and the reflected ultrasound at critical angles. Two laser beams were used, one being diffracted by the incident ultrasound, the other being diffracted by the reflected ultrasound. Information concerning the geometrical shape of the sample as well as information concerning the thickness of a thin layer could be obtained from measurements in the near-field of the light diffraction. In this letter it is shown that using only one laser beam, traveling through the intersection region of both ultrasounds, exact thickness information of the layer can be obtained. Theoretical calculations are derived and compared with practical measurements for a 3 m copper layer on a stainless-steel plate.
Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutan... more Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutaneous implants. The feasibility of monitoring bone remodelling in vivo by microfocus computed tomography was assessed experimentally. A microfocus computed tomography (μCT) protocol was developed to minimise the side effects (i.e. radionecrosis) while maintaining sufficient image quality to allow segmentation of the μCT slices for subsequent processing into finite element models.
To introduce a multimodular combination of techniques as a novel minimal invasive approach to inv... more To introduce a multimodular combination of techniques as a novel minimal invasive approach to investigate efficiently and accurately external cervical resorption (ECR). One case of a central incisor with extensive external cervical resorption was selected to demonstrate the potential of a comparative novel study methodology. ECR diagnosis was based on clinical inspection, digital radiography and cone-beam computed tomography (CBCT). After extraction the tooth was investigated using micro-focus computed tomography (micro-CT), nano-CT and hard tissue histology. These techniques were compared for their accuracy and applicability to highlight their advantages and disadvantages. Nano-CT was more effective than micro-CT and CBCT for detailed ex vivo exploration of ECR. The reparative tissue, pericanalar resorption resistant sheet (PRRS), pulp tissue reactions, resorption channels and their interconnection with the periodontal ligament space, were accurately visualised by detailed processi...
The impact of sugar (17.6-31.2%) and fat (8.7-15.8%) levels on cookie structure was studied. Cook... more The impact of sugar (17.6-31.2%) and fat (8.7-15.8%) levels on cookie structure was studied. Cookie diameter increased and its height decreased with increasing sugar or fat levels. X-ray microfocus computed tomography porosities and cell sizes increased with fat level, but cell size distribution, cell wall thickness and distribution were not affected by fat level, indicating that fat primarily incorporates air. In contrast, the sugar level influenced porosity, cell size, cell wall thickness and their relative distributions. Thus, the sucrose level, probably by affecting dough viscosity during baking, largely influences the baked cookie structure. Cell and cell wall anisotropy measurements indicated that the inner orientation of cells and cell walls probably depends on the horizontal spread behaviour, rather than on the maximum cookie height and collapse. Finally, the surface cracking pattern was determined by sugar level, rather than by structural collapse at the end of baking.
Objective: One of the early hallmarks of osteoarthritis (OA) is a progressive degeneration of the... more Objective: One of the early hallmarks of osteoarthritis (OA) is a progressive degeneration of the articular cartilage. Early diagnosis of OA-associated cartilage alterations would be beneficial for disease prevention and control, and for the development of disease-modifying treatments. However, early diagnosis is still hampered by a lack of quantifiable readouts in preclinical models. Design: In this study, we have shown the potency of contrast-enhanced nanofocus x-ray computed tomography (CE-nanoCT) to be used for virtual 3-dimensional (3D) histopathology in established mouse models for OA, and we compared with standard histopathology. Results: We showed the equivalence of CE-nanoCT images to histopathology for the modified Mankin scoring of the cartilage structure and quality. Additionally, a limited set of 3D cartilage characteristics measured by CE-nanoCT image analysis in a user-independent and semiautomatic manner, that is, average and maximum of the noncalcified cartilage thickness distribution and loss in glycosaminoglycans, was shown to be predictive for the cartilage quality and structure as can be evaluated by histopathological scoring through the use of an empirical model. Conclusions: We have shown that CE-nanoCT is a tool that allows virtual histopathology and 3D morphological quantification of multitissue systems, such as the chondro-osseous junction. It provides faster and more quantitative data on cartilage structure and quality compared with standard histopathology while eliminating user bias. CE-nanoCT thus should allow capturing subtle differences in cartilage characteristics, carefully mapping OA progression and, ultimately, asses the beneficial changes when testing a candidate disease-modifying treatment.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2012
Understanding the mechanism of crack propagation during bone cutting is necessary for the develop... more Understanding the mechanism of crack propagation during bone cutting is necessary for the development of realistic bone cutting models. This article studies the on-line fractural behaviour of cortical bone caused by penetration with a sharp metallic wedge mounted on an on-line loading stage within an X-ray microfocus computed tomography system. The experimental results demonstrated anisotropy in crack propagation depending on the penetration direction with regard to the longitudinal bone axis and relate the crack growth to the extent of penetration. Scanning electron microscopy is performed to analyse the mechanism of cracking in the two phase microstructure of compact bone.
An intensity modulated sensor, based on the microbending concept, has been incorporated in lamina... more An intensity modulated sensor, based on the microbending concept, has been incorporated in laminates produced from a C/epoxy prepreg. Pencil lead break tests (Hsu-Neilsen sources) and tensile tests have been performed on this material. In this research study, fibre optic sensors will be proven to offer an alternative for the robust piezoelectric transducers used for Acoustic Emission (AE) monitoring. The main emphasis has been put on the use of advanced signal processing techniques based on time-frequency analysis. The signal Short Time Fourier Transform (STFT) has been computed and several robust noise reduction algorithms, such as Wiener adaptive filtering, improved spectral subtraction filtering, and Singular Value Decomposition (SVD) -based filtering, have been applied. An energy and frequency -based detection criterion is put forward to detect transient signals that can be correlated with Modal Acoustic Emission (MAE) results and thus damage in the composite material. There is a strong indication that time-frequency analysis and the Hankel Total Least Squares (HTLS) method can also be used for damage characterisation. This study shows that the signal from a quite simple microbend optical sensor contains information on the elastic energy released whenever damage is being introduced in the host material by mechanical loading. Robust algorithms can be used to retrieve and analyse this information.
The paper focuses on the area of context modeling with respect to the specification of context-aw... more The paper focuses on the area of context modeling with respect to the specification of context-aware systems supporting ubiquitous applications. The proposed approach, followed within the SIMPLICITY IST project, uses a high-level system ontology to derive context models for system components which consequently are mapped to the system's physical entities. For the definition of user and device-related context models in particular, the paper suggests a standard-based process consisting of an analysis phase using the Common Information Model (CIM) methodology followed by an implementation phase that defines 3GPP based components. The benefits of this approach are further depicted by preliminary examples of XML grammars defining profiles and components, component instances, coupled with descriptions of respective ubiquitous applications
... ACKNOWLEDGEMENT Marnix Surgeon wishes to thank the Flemish IWT for granting him a research fe... more ... ACKNOWLEDGEMENT Marnix Surgeon wishes to thank the Flemish IWT for granting him a research fellowship. REFERENCES ... Dublin, 125–130. 8. Liu, K., Ferguson, SM and Measures, RM 1989. SPIE Vol. 1170 Fibre Optic Smart Structures and Skins II, 205–210. ...
The establishment of reliable correlations between the extend of damage and a sensor response usi... more The establishment of reliable correlations between the extend of damage and a sensor response using automated non destructive testing (structural health monitoring) is the first aim of the present paper. The second and its main aim is the estimation of the efficiency of different approaches of the fatigue crack prediction when scalar parameters are used to represent the signal-response. Investigation of ultrasonic Lamb wave interaction with a fatigue crack has been performed on thin sheets (1mm) of aluminum alloy (2024-Т3). Three parameters of response were selected to compare efficiency and the standard deviation of a predicted fatigue crack was used for comparison. Quite definitely it is possible to conclude, that the proposed technology is capable of providing high stability and necessary accuracy at the continuous integrated SHM of thin-walled aluminum components of aircraft. It is also shown that the accuracy of damage prediction is one of the most significant parameter of SHM efficiency. It can be used as the main criterion at selection of diagnostic parameters for continuous integrated monitoring of structural elements of aircraft.
The acoustic emission (AE) technique is used for investigating the interfacial fracture and damag... more The acoustic emission (AE) technique is used for investigating the interfacial fracture and damage propagation in GFRP-and SRG-strengthened bricks during debonding tests. The bond behavior is investigated through single-lap shear bond tests and the fracture progress during the tests is recorded by means of AE sensors. The fracture progress and active debonding mechanisms are characterized in both specimen types with the aim of AE outputs. Moreover, a clear distinction between the AE outputs of specimens with different failure modes, in both SRG-and GFRPstrengthened specimens, is found which allows characterizing the debonding failure mode based on acoustic emission data.
A phenomenon which has been termed ''multilayered Rayleigh modes'' has been presented in previous... more A phenomenon which has been termed ''multilayered Rayleigh modes'' has been presented in previous papers. This study aims to prove experimentally the existence of these waves in anisotropic periodically multilayered media. These modes result from a combination of Floquet waves which propagate in a periodically multilayered medium when all the Floquet waves are inhomogeneous. The experimental verification was done using an acousto-optic technique and a measurement of the reflected field, which was obtained with a hydrophone measurement system, on a carbon/epoxy composite plate. The experimental and calculated dispersion curves of the multilayered Rayleigh modes were then drawn. The coincidence of the curves was found quite good, thus confirming our theory. However, two modes were found by the acousto-optic technique not to fit into the theory. One experimentally detected mode was found to correspond to the Lamb mode of the plate and the other was not experimentally detected by the acousto-optic technique. Measurement of the reflected field for this mode, which was obtained with a hydrophone measurement system, and its comparison with the predicted reflected field make it possible to verify the existence of the mode. The combination of both experiments permit a good coincidence to be found.
The acousto-optic technique presented by Wevers, Devolder, Leroy, and De Meester ͓Appl. Phys. Let... more The acousto-optic technique presented by Wevers, Devolder, Leroy, and De Meester ͓Appl. Phys. Lett. 66, 1466 ͑1995͔͒ was based on the information concerning the phase shift between the incident and the reflected ultrasound at critical angles. Two laser beams were used, one being diffracted by the incident ultrasound, the other being diffracted by the reflected ultrasound. Information concerning the geometrical shape of the sample as well as information concerning the thickness of a thin layer could be obtained from measurements in the near-field of the light diffraction. In this letter it is shown that using only one laser beam, traveling through the intersection region of both ultrasounds, exact thickness information of the layer can be obtained. Theoretical calculations are derived and compared with practical measurements for a 3 m copper layer on a stainless-steel plate.
Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutan... more Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutaneous implants. The feasibility of monitoring bone remodelling in vivo by microfocus computed tomography was assessed experimentally. A microfocus computed tomography (μCT) protocol was developed to minimise the side effects (i.e. radionecrosis) while maintaining sufficient image quality to allow segmentation of the μCT slices for subsequent processing into finite element models.
To introduce a multimodular combination of techniques as a novel minimal invasive approach to inv... more To introduce a multimodular combination of techniques as a novel minimal invasive approach to investigate efficiently and accurately external cervical resorption (ECR). One case of a central incisor with extensive external cervical resorption was selected to demonstrate the potential of a comparative novel study methodology. ECR diagnosis was based on clinical inspection, digital radiography and cone-beam computed tomography (CBCT). After extraction the tooth was investigated using micro-focus computed tomography (micro-CT), nano-CT and hard tissue histology. These techniques were compared for their accuracy and applicability to highlight their advantages and disadvantages. Nano-CT was more effective than micro-CT and CBCT for detailed ex vivo exploration of ECR. The reparative tissue, pericanalar resorption resistant sheet (PRRS), pulp tissue reactions, resorption channels and their interconnection with the periodontal ligament space, were accurately visualised by detailed processi...
The impact of sugar (17.6-31.2%) and fat (8.7-15.8%) levels on cookie structure was studied. Cook... more The impact of sugar (17.6-31.2%) and fat (8.7-15.8%) levels on cookie structure was studied. Cookie diameter increased and its height decreased with increasing sugar or fat levels. X-ray microfocus computed tomography porosities and cell sizes increased with fat level, but cell size distribution, cell wall thickness and distribution were not affected by fat level, indicating that fat primarily incorporates air. In contrast, the sugar level influenced porosity, cell size, cell wall thickness and their relative distributions. Thus, the sucrose level, probably by affecting dough viscosity during baking, largely influences the baked cookie structure. Cell and cell wall anisotropy measurements indicated that the inner orientation of cells and cell walls probably depends on the horizontal spread behaviour, rather than on the maximum cookie height and collapse. Finally, the surface cracking pattern was determined by sugar level, rather than by structural collapse at the end of baking.
Objective: One of the early hallmarks of osteoarthritis (OA) is a progressive degeneration of the... more Objective: One of the early hallmarks of osteoarthritis (OA) is a progressive degeneration of the articular cartilage. Early diagnosis of OA-associated cartilage alterations would be beneficial for disease prevention and control, and for the development of disease-modifying treatments. However, early diagnosis is still hampered by a lack of quantifiable readouts in preclinical models. Design: In this study, we have shown the potency of contrast-enhanced nanofocus x-ray computed tomography (CE-nanoCT) to be used for virtual 3-dimensional (3D) histopathology in established mouse models for OA, and we compared with standard histopathology. Results: We showed the equivalence of CE-nanoCT images to histopathology for the modified Mankin scoring of the cartilage structure and quality. Additionally, a limited set of 3D cartilage characteristics measured by CE-nanoCT image analysis in a user-independent and semiautomatic manner, that is, average and maximum of the noncalcified cartilage thickness distribution and loss in glycosaminoglycans, was shown to be predictive for the cartilage quality and structure as can be evaluated by histopathological scoring through the use of an empirical model. Conclusions: We have shown that CE-nanoCT is a tool that allows virtual histopathology and 3D morphological quantification of multitissue systems, such as the chondro-osseous junction. It provides faster and more quantitative data on cartilage structure and quality compared with standard histopathology while eliminating user bias. CE-nanoCT thus should allow capturing subtle differences in cartilage characteristics, carefully mapping OA progression and, ultimately, asses the beneficial changes when testing a candidate disease-modifying treatment.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2012
Understanding the mechanism of crack propagation during bone cutting is necessary for the develop... more Understanding the mechanism of crack propagation during bone cutting is necessary for the development of realistic bone cutting models. This article studies the on-line fractural behaviour of cortical bone caused by penetration with a sharp metallic wedge mounted on an on-line loading stage within an X-ray microfocus computed tomography system. The experimental results demonstrated anisotropy in crack propagation depending on the penetration direction with regard to the longitudinal bone axis and relate the crack growth to the extent of penetration. Scanning electron microscopy is performed to analyse the mechanism of cracking in the two phase microstructure of compact bone.
An intensity modulated sensor, based on the microbending concept, has been incorporated in lamina... more An intensity modulated sensor, based on the microbending concept, has been incorporated in laminates produced from a C/epoxy prepreg. Pencil lead break tests (Hsu-Neilsen sources) and tensile tests have been performed on this material. In this research study, fibre optic sensors will be proven to offer an alternative for the robust piezoelectric transducers used for Acoustic Emission (AE) monitoring. The main emphasis has been put on the use of advanced signal processing techniques based on time-frequency analysis. The signal Short Time Fourier Transform (STFT) has been computed and several robust noise reduction algorithms, such as Wiener adaptive filtering, improved spectral subtraction filtering, and Singular Value Decomposition (SVD) -based filtering, have been applied. An energy and frequency -based detection criterion is put forward to detect transient signals that can be correlated with Modal Acoustic Emission (MAE) results and thus damage in the composite material. There is a strong indication that time-frequency analysis and the Hankel Total Least Squares (HTLS) method can also be used for damage characterisation. This study shows that the signal from a quite simple microbend optical sensor contains information on the elastic energy released whenever damage is being introduced in the host material by mechanical loading. Robust algorithms can be used to retrieve and analyse this information.
The paper focuses on the area of context modeling with respect to the specification of context-aw... more The paper focuses on the area of context modeling with respect to the specification of context-aware systems supporting ubiquitous applications. The proposed approach, followed within the SIMPLICITY IST project, uses a high-level system ontology to derive context models for system components which consequently are mapped to the system's physical entities. For the definition of user and device-related context models in particular, the paper suggests a standard-based process consisting of an analysis phase using the Common Information Model (CIM) methodology followed by an implementation phase that defines 3GPP based components. The benefits of this approach are further depicted by preliminary examples of XML grammars defining profiles and components, component instances, coupled with descriptions of respective ubiquitous applications
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Papers by Martine Wevers