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Papers by Dimitri Donskoy

Up to 90 percent of failures of in-service metallic structures happen due to fatigue cracks. A fa... more Up to 90 percent of failures of in-service metallic structures happen due to fatigue cracks. A fatigue crack starts as a damage precursor at un-perceivable levels (such as molecular dislocation or micro cracking) when the material is subjected to repeated loading. The crack can often continue to grow to a critical size without sufficient warning, causing total failure of a structural component. Structural Health Monitoring (SHM) and Non-Destructive Evaluation (NDE) techniques are frequently used to identify, monitor and assess the evolution of damage. Today’s methods are applicable to small areas of the component and are not sensitive to the earliest evolution of damage.

Journal of Sound and Vibration

Vibro-Acoustic Modulation method for detection and characterization of various structural and mat... more Vibro-Acoustic Modulation method for detection and characterization of various structural and material flaws has been actively researched for the last two decades. Most of the studies focused on detection and monitoring of macro-cracks requiring well established baseline (no-damage) value of the modulation index. The baseline value is specific for a particular structure, measuring setup, and other factors and can't be established in many practical situations without a long term monitoring looking for a relative change in the Modulation Index. In this work, we propose and investigate a baseline-free Vibro-Acoustic Modulation method, which does not require monitoring of relative Modulation Index change, unlike conventional approach. It was hypothesized that the nonlinear mechanisms (and respective nonlinear response) of a structure are different for undamaged and damaged material. For example: material without damage or at early stages of fatigue have classic elastic or hysteretic/dissipative nonlinearity while damaged (cracked) material may exhibit contact bi-linear or Hertzian nonlinear mechanisms. These mechanisms yield different power law dependencies of Modulation Index (MI) as function of applied vibration frequency input amplitude, B: MI ~ B β. Thus, quadratic nonlinearity yields linear dependence, β =1, and Hertzian nonlinearity results in β<1. Other nonlinear mechanisms yield different power laws. Therefore, measuring power damage coefficient β instead of MI may offer testing without established reference value. It is also offer some insights into the nonlinear mechanisms transformation during damage evolution. This approach was experimentally investigated and validated.

Steel Construction

This paper explores a new interdisciplinary method for internal damage detection and tracking in ... more This paper explores a new interdisciplinary method for internal damage detection and tracking in composite materials using thermo-chemical sensing. A micro-sized network of strings is interwoven into the composites. Each string consists of a pair of tubes containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in direct contact between the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. When exposed to a microwave energy source, a polar product heats up dramatically within seconds in comparison to the surrounding composite material or the non-polar reactants. This localized thermal signature can be rendered visible by an infrared camera. This study summarizes the findings of an in-depth computational and experimental study of this sensing technology which is expected to be applicable across industries using composites, among them aerospace, automotive, offshore and bridge engineering. Potential applications in steel offshore or steel bridge engineering involve using composite sensing patches to cover fatigue fracture-critical components. Defects initiating on the steel substrate surface are expected to be sensed on demand with this proposed sensing technology.

Structural Health Monitoring 2015, 2015

The motivation for this research is a lack of accurate, efficient and costeffective methodology t... more The motivation for this research is a lack of accurate, efficient and costeffective methodology to detect internal defects in composite plates. A micro-size network of strings is interwoven into the composites. Each string consists of a pair of tubes, containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in the direct contact of the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. Our preliminary investigation shows that a polar product, when exposed to a microwave energy source, heats up dramatically in comparison to the ambient composite material or the non-polar reactants. Our proposed structure-health monitoring approach builds upon this finding by using a short term low-power microwave exposure, causing a local high-thermal signature along potential internal defects. The elevated temperature regions are visualized with an infrared camera. The research presented in this paper has the following objectives: (a) We introduce adequate non-polar reactants and quantify the temperature sensitivity of the polar product. (b) We investigate the optimized microstructure and material of the double-cell tube and fine-tune the design to enable fracturing of the cell walls under certain strain and ease embedment into the composites. (c) The paper sheds light on potential manufacturing processes of the micro-size sensing network per se as well as the embedment into the composites. The clear advantages of this methodology over others are that it provides large area coverage, has no requirement for an internal power source and wiring and hence does not compromise the structural integrity of the composites. doi: 10.12783/SHM2015/214

Transportation Research Record: Journal of the Transportation Research Board

The increasing probability of collapse in defective structures owing to aging is one of the major... more The increasing probability of collapse in defective structures owing to aging is one of the major issues in transportation. Therefore, different methodologies that are capable of monitoring structural components have been used to identify defects and predict failure. Among these methods, the non-linear vibro-acoustic modulation (VAM) technique has been implemented for many years in a variety of industries, such as aerospace. This method utilizes the effect of nonlinear interactions between a high frequency ultrasonic wave (carrier signal) and a much lower frequency structural vibration (modulating signal). This interaction takes place at nonlinear interfaces (cracks, bolted connections, delaminations, etc.) manifesting itself in the spectrum as side-band components around the carrier frequency. In this study, the VAM method was investigated as a non-destructive evaluation (NDE) method for fracture critical members (FCMs) in steel bridges. The results of the experimental studies reve...

The Vibro-Acoustic Modulation (VAM) method utilizes nonlinear interaction of a high frequency ult... more The Vibro-Acoustic Modulation (VAM) method utilizes nonlinear interaction of a high frequency ultrasonic wave (carrier signal) with frequency ω and a low frequency modulating vibration with frequency Ω << ω, in the presence of various flaws such as fatigue and stress-corrosion cracks, disbonds, etc. Most of the reported VAM studies correlate flaw presence and growth with the increase in the Modulation Index (MI) defined in the spectral domain as the ratio of the side-band spectral components at frequencies ω±Ω to the amplitude of the carrier. This approach, however, does not differentiate between amplitude, AM, or frequency, FM, modulations contributing to the MI. It has been assumed that the prevailing modulation is AM due to contact-type nonlinear mechanisms. However, there could be other mechanisms leading to phase/frequency modulation. The present study aims to develop an algorithm of AM/FM separation specifically for the VAM method. It is shown that the commonly used Hilbert Transform (HT) separation may not work for a typical VAM scenario. The developed In-phase/Quadrature Homodyne Separation algorithm addresses HT shortcomings. The algorithm has been tested both numerically and experimentally (for fatigue crack evolution) showing FM dominance at initial micro-crack growth stages and transition to AM dominance during macro-crack formation.

AIP Conference Proceedings, 2008

ABSTRACT

AIP Conference Proceedings, 2004

ABSTRACT

J Acoust Soc Amer, 2001

The most commonly used devices for land mine detection are metal detectors that work by measuring... more The most commonly used devices for land mine detection are metal detectors that work by measuring the disturbance of an emitted electromagnetic field caused by the presence of metallic objects in the ground. For ferromagnetic objects, magnetometers are employed. These sensors measure the disturbance of the earth's natural electromagnetic field. Neither of these types of detectors can differentiate a mine from metallic debris; this leads to up to 1000 false alarms for each real mine. In addition, most modern antipersonnel mines are made out of plastic or wood with very few metal parts in them, so the metal detectors cannot detect them. Newer methods conceived to detect mines involve ground-penetrating radar, infrared imaging, X-ray backscattering, thermal neutron activation, and some others. Most of these methods rely on imaging and very often cannot differentiate a mine from rocks and other debris. The drawbacks of the other non-imaging techniques, such as thermal neutron activation, apart from system complexity, are the limited depth of penetration and the potential environmental and health danger. Acoustic methods of detecting mines were always a primary approach for underwater mine detection. However, earlier attempts to use acoustic energy for land mine detection were not successful due to a number of deficiencies. One method, House and Pape [1], identifies a buried object by viewing the images of the acoustic energy reflected from the soil and, therefore, is unable to differentiate a mine from debris with similar acoustic reflectivity. Other methods, Rogers and Don [2] and Caulfield [3], are based on the

The Journal of the Acoustical Society of America, Jun 1, 2002

The most commonly used devices for land mine detection are metal detectors that work by measuring... more The most commonly used devices for land mine detection are metal detectors that work by measuring the disturbance of an emitted electromagnetic field caused by the presence of metallic objects in the ground. For ferromagnetic objects, magnetometers are employed. These sensors measure the disturbance of the earth's natural electromagnetic field. Neither of these types of detectors can differentiate a mine from metallic debris; this leads to up to 1000 false alarms for each real mine. In addition, most modern antipersonnel mines are made out of plastic or wood with very few metal parts in them, so the metal detectors cannot detect them. Newer methods conceived to detect mines involve ground-penetrating radar, infrared imaging, X-ray backscattering, thermal neutron activation, and some others. Most of these methods rely on imaging and very often cannot differentiate a mine from rocks and other debris. The drawbacks of the other non-imaging techniques, such as thermal neutron activation, apart from system complexity, are the limited depth of penetration and the potential environmental and health danger. Acoustic methods of detecting mines were always a primary approach for underwater mine detection. However, earlier attempts to use acoustic energy for land mine detection were not successful due to a number of deficiencies. One method, House and Pape [1], identifies a buried object by viewing the images of the acoustic energy reflected from the soil and, therefore, is unable to differentiate a mine from debris with similar acoustic reflectivity. Other methods, Rogers and Don [2] and Caulfield [3], are based on the

Journal of the Acoustical Society of America, 2016

AIP Conference Proceedings, 2008

[AIP Conference Proceedings 1022, 513 (2008)]. Dimitri M. Donskoy. Abstract. ... The paper provid... more [AIP Conference Proceedings 1022, 513 (2008)]. Dimitri M. Donskoy. Abstract. ... The paper provides overview of theoretical and experimental investigations conducted by the author and his colleagues at Stevens Institute of Technology with emphasis on the nonlinear detection. ...

Up to 90 percent of failures of in-service metallic structures happen due to fatigue cracks. A fa... more Up to 90 percent of failures of in-service metallic structures happen due to fatigue cracks. A fatigue crack starts as a damage precursor at un-perceivable levels (such as molecular dislocation or micro cracking) when the material is subjected to repeated loading. The crack can often continue to grow to a critical size without sufficient warning, causing total failure of a structural component. Structural Health Monitoring (SHM) and Non-Destructive Evaluation (NDE) techniques are frequently used to identify, monitor and assess the evolution of damage. Today’s methods are applicable to small areas of the component and are not sensitive to the earliest evolution of damage.

Journal of Sound and Vibration

Vibro-Acoustic Modulation method for detection and characterization of various structural and mat... more Vibro-Acoustic Modulation method for detection and characterization of various structural and material flaws has been actively researched for the last two decades. Most of the studies focused on detection and monitoring of macro-cracks requiring well established baseline (no-damage) value of the modulation index. The baseline value is specific for a particular structure, measuring setup, and other factors and can't be established in many practical situations without a long term monitoring looking for a relative change in the Modulation Index. In this work, we propose and investigate a baseline-free Vibro-Acoustic Modulation method, which does not require monitoring of relative Modulation Index change, unlike conventional approach. It was hypothesized that the nonlinear mechanisms (and respective nonlinear response) of a structure are different for undamaged and damaged material. For example: material without damage or at early stages of fatigue have classic elastic or hysteretic/dissipative nonlinearity while damaged (cracked) material may exhibit contact bi-linear or Hertzian nonlinear mechanisms. These mechanisms yield different power law dependencies of Modulation Index (MI) as function of applied vibration frequency input amplitude, B: MI ~ B β. Thus, quadratic nonlinearity yields linear dependence, β =1, and Hertzian nonlinearity results in β<1. Other nonlinear mechanisms yield different power laws. Therefore, measuring power damage coefficient β instead of MI may offer testing without established reference value. It is also offer some insights into the nonlinear mechanisms transformation during damage evolution. This approach was experimentally investigated and validated.

Steel Construction

This paper explores a new interdisciplinary method for internal damage detection and tracking in ... more This paper explores a new interdisciplinary method for internal damage detection and tracking in composite materials using thermo-chemical sensing. A micro-sized network of strings is interwoven into the composites. Each string consists of a pair of tubes containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in direct contact between the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. When exposed to a microwave energy source, a polar product heats up dramatically within seconds in comparison to the surrounding composite material or the non-polar reactants. This localized thermal signature can be rendered visible by an infrared camera. This study summarizes the findings of an in-depth computational and experimental study of this sensing technology which is expected to be applicable across industries using composites, among them aerospace, automotive, offshore and bridge engineering. Potential applications in steel offshore or steel bridge engineering involve using composite sensing patches to cover fatigue fracture-critical components. Defects initiating on the steel substrate surface are expected to be sensed on demand with this proposed sensing technology.

Structural Health Monitoring 2015, 2015

The motivation for this research is a lack of accurate, efficient and costeffective methodology t... more The motivation for this research is a lack of accurate, efficient and costeffective methodology to detect internal defects in composite plates. A micro-size network of strings is interwoven into the composites. Each string consists of a pair of tubes, containing one of two different non-polar reactants. A local defect within the composites causes straining and cracking of the tube shell, resulting in the direct contact of the two non-polar reactants. The latter undergo a chemical reaction resulting in a polar product. Our preliminary investigation shows that a polar product, when exposed to a microwave energy source, heats up dramatically in comparison to the ambient composite material or the non-polar reactants. Our proposed structure-health monitoring approach builds upon this finding by using a short term low-power microwave exposure, causing a local high-thermal signature along potential internal defects. The elevated temperature regions are visualized with an infrared camera. The research presented in this paper has the following objectives: (a) We introduce adequate non-polar reactants and quantify the temperature sensitivity of the polar product. (b) We investigate the optimized microstructure and material of the double-cell tube and fine-tune the design to enable fracturing of the cell walls under certain strain and ease embedment into the composites. (c) The paper sheds light on potential manufacturing processes of the micro-size sensing network per se as well as the embedment into the composites. The clear advantages of this methodology over others are that it provides large area coverage, has no requirement for an internal power source and wiring and hence does not compromise the structural integrity of the composites. doi: 10.12783/SHM2015/214

Transportation Research Record: Journal of the Transportation Research Board

The increasing probability of collapse in defective structures owing to aging is one of the major... more The increasing probability of collapse in defective structures owing to aging is one of the major issues in transportation. Therefore, different methodologies that are capable of monitoring structural components have been used to identify defects and predict failure. Among these methods, the non-linear vibro-acoustic modulation (VAM) technique has been implemented for many years in a variety of industries, such as aerospace. This method utilizes the effect of nonlinear interactions between a high frequency ultrasonic wave (carrier signal) and a much lower frequency structural vibration (modulating signal). This interaction takes place at nonlinear interfaces (cracks, bolted connections, delaminations, etc.) manifesting itself in the spectrum as side-band components around the carrier frequency. In this study, the VAM method was investigated as a non-destructive evaluation (NDE) method for fracture critical members (FCMs) in steel bridges. The results of the experimental studies reve...

The Vibro-Acoustic Modulation (VAM) method utilizes nonlinear interaction of a high frequency ult... more The Vibro-Acoustic Modulation (VAM) method utilizes nonlinear interaction of a high frequency ultrasonic wave (carrier signal) with frequency ω and a low frequency modulating vibration with frequency Ω << ω, in the presence of various flaws such as fatigue and stress-corrosion cracks, disbonds, etc. Most of the reported VAM studies correlate flaw presence and growth with the increase in the Modulation Index (MI) defined in the spectral domain as the ratio of the side-band spectral components at frequencies ω±Ω to the amplitude of the carrier. This approach, however, does not differentiate between amplitude, AM, or frequency, FM, modulations contributing to the MI. It has been assumed that the prevailing modulation is AM due to contact-type nonlinear mechanisms. However, there could be other mechanisms leading to phase/frequency modulation. The present study aims to develop an algorithm of AM/FM separation specifically for the VAM method. It is shown that the commonly used Hilbert Transform (HT) separation may not work for a typical VAM scenario. The developed In-phase/Quadrature Homodyne Separation algorithm addresses HT shortcomings. The algorithm has been tested both numerically and experimentally (for fatigue crack evolution) showing FM dominance at initial micro-crack growth stages and transition to AM dominance during macro-crack formation.

AIP Conference Proceedings, 2008

ABSTRACT

AIP Conference Proceedings, 2004

ABSTRACT

J Acoust Soc Amer, 2001

The most commonly used devices for land mine detection are metal detectors that work by measuring... more The most commonly used devices for land mine detection are metal detectors that work by measuring the disturbance of an emitted electromagnetic field caused by the presence of metallic objects in the ground. For ferromagnetic objects, magnetometers are employed. These sensors measure the disturbance of the earth's natural electromagnetic field. Neither of these types of detectors can differentiate a mine from metallic debris; this leads to up to 1000 false alarms for each real mine. In addition, most modern antipersonnel mines are made out of plastic or wood with very few metal parts in them, so the metal detectors cannot detect them. Newer methods conceived to detect mines involve ground-penetrating radar, infrared imaging, X-ray backscattering, thermal neutron activation, and some others. Most of these methods rely on imaging and very often cannot differentiate a mine from rocks and other debris. The drawbacks of the other non-imaging techniques, such as thermal neutron activation, apart from system complexity, are the limited depth of penetration and the potential environmental and health danger. Acoustic methods of detecting mines were always a primary approach for underwater mine detection. However, earlier attempts to use acoustic energy for land mine detection were not successful due to a number of deficiencies. One method, House and Pape [1], identifies a buried object by viewing the images of the acoustic energy reflected from the soil and, therefore, is unable to differentiate a mine from debris with similar acoustic reflectivity. Other methods, Rogers and Don [2] and Caulfield [3], are based on the

The Journal of the Acoustical Society of America, Jun 1, 2002

The most commonly used devices for land mine detection are metal detectors that work by measuring... more The most commonly used devices for land mine detection are metal detectors that work by measuring the disturbance of an emitted electromagnetic field caused by the presence of metallic objects in the ground. For ferromagnetic objects, magnetometers are employed. These sensors measure the disturbance of the earth's natural electromagnetic field. Neither of these types of detectors can differentiate a mine from metallic debris; this leads to up to 1000 false alarms for each real mine. In addition, most modern antipersonnel mines are made out of plastic or wood with very few metal parts in them, so the metal detectors cannot detect them. Newer methods conceived to detect mines involve ground-penetrating radar, infrared imaging, X-ray backscattering, thermal neutron activation, and some others. Most of these methods rely on imaging and very often cannot differentiate a mine from rocks and other debris. The drawbacks of the other non-imaging techniques, such as thermal neutron activation, apart from system complexity, are the limited depth of penetration and the potential environmental and health danger. Acoustic methods of detecting mines were always a primary approach for underwater mine detection. However, earlier attempts to use acoustic energy for land mine detection were not successful due to a number of deficiencies. One method, House and Pape [1], identifies a buried object by viewing the images of the acoustic energy reflected from the soil and, therefore, is unable to differentiate a mine from debris with similar acoustic reflectivity. Other methods, Rogers and Don [2] and Caulfield [3], are based on the

Journal of the Acoustical Society of America, 2016

AIP Conference Proceedings, 2008

[AIP Conference Proceedings 1022, 513 (2008)]. Dimitri M. Donskoy. Abstract. ... The paper provid... more [AIP Conference Proceedings 1022, 513 (2008)]. Dimitri M. Donskoy. Abstract. ... The paper provides overview of theoretical and experimental investigations conducted by the author and his colleagues at Stevens Institute of Technology with emphasis on the nonlinear detection. ...