Jeremy S. Knopp

Bio: Jeremy S. Knopp is an academic researcher from Air Force Research Laboratory. The author has contributed to research in topics: Eddy current & Structural health monitoring. The author has an hindex of 15, co-authored 90 publications receiving 591 citations.

Investigation of a Model‐Assisted Approach to Probability of Detection Evaluation

Abstract: This paper presents a model‐assisted probability of detection (MAPOD) study for inspection of a two‐layer airframe structure. Eddy current measurements for varying crack length around fastener holes in a two‐layer aluminum structure are studied using both experimental and model‐generated data. New statistical algorithms are used to calculate the probability of detection. Good agreement was achieved between empirical and model‐assisted approaches.

Model-Assisted Probability of Detection Evaluation for Eddy Current Inspection of Fastener Sites

Abstract: A model‐assisted approach for the design and execution of probability of detection (POD) studies is proposed. General agreement was achieved between experimental and full‐model assisted results for eddy current inspection of cracks at fastener sites located at both the first and second layers. The accuracy of the POD results was found to be dependent upon the NDE model and assumptions in the model‐assisted POD evaluation. Insight is presented for improving the quality of future studies.

Protocol for Reliability Assessment of Structural Health Monitoring Systems Incorporating Model-Assisted Probability of Detection (MAPOD) Approach

Abstract: This paper will describe the progress in the development of a methodology for reliability assessment for SHM systems. The methodology consists of the development and use of appropriate statistical metrics of reliability for SHM systems that detect, localize, and/or size damage, and a protocol designed for utilizing empirical data, models, simulations, and uncertainty analyses for statistically characterizing these systems. The protocol comprises several critical steps: a procedure for analyzing all pertinent characteristics of the SHM system to identify the critical factors that affect system performance, a multistage approach to system validation, a modeling and experimental methodology for efficiently addressing a wide range of damage and operational conditions, and effective methods for evaluating the appropriate metrics of reliability depending on the SHM system type and function. A critical aspect of the protocol is that by addressing variability in the model and minimizing unexplained error in the representation, less experimental data will be required to address the total unknowns in the evaluation. The application of these methods in the protocol will be presented in detail including several demonstrations using simulation-based case studies.

Computational methods in eddy current crack detection at fastener sites in multi-layer structures

Abstract: Reliable detection of both surface and subsurface cracks around fastener sites continues to be a need for maintaining ageing aircraft structures. In this work, a comprehensive overview of both experimental and modelling work addressing eddy current crack detection around fastener holes in multi-layer structures is presented. This overview consists of a strategy for the application of computational methods along with case studies that demonstrate the role of modelling for this particular class of problems. The state-of-the-art on eddy current modelling applicable to low-frequency eddy current problems is reviewed. The role of modelling in feature extraction algorithm development, crack characterisation, and probability of detection evaluation is highlighted.

Guided wave based structural health monitoring: A review

Abstract: The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

Assessment of delay-and-sum algorithms for damage detection in aluminium and composite plates

Abstract: Piezoelectric sensors are increasingly being used in active structural health monitoring, due to their durability, light weight and low power consumption. In the present work damage detection and characterization methodologies based on Lamb waves have been evaluated for aircraft panels. The applicability of various proposed delay-and-sum algorithms on isotropic and composite stiffened panels have been investigated, both numerically and experimentally. A numerical model for ultrasonic wave propagation in composite laminates is proposed and compared to signals recorded from experiments. A modified delay-and-sum algorithm is then proposed for detecting impact damage in composite plates with and without a stiffener which is shown to capture and localize damage with only four transducers.

Damage detection sensitivity characterization of acousto-ultrasound-based structural health monitoring techniques:

Abstract: Reliability quantification is a critical and necessary process for the evaluation and assessment of any inspection technology that may be classified either as a nondestructive evaluation or structural health monitoring technique. Based on the sensitivity characterization of nondestructive evaluation techniques, appropriate processes have been developed and established for the reliability quantification of their performance with respect to damage/flaw detection in materials or structures. However, in the case of structural health monitoring methods, no such well-defined and general applicable approaches have been established for neither active nor passive sensing techniques that allow for their accurate reliability quantification. The objective of this study is to characterize the sensitivity of active-sensing acousto-ultrasound-based structural health monitoring techniques with respect to damage detection, as well as to identify the parameters that influence their sensitivity. With such an understanding, ...

Structural health monitoring of fatigue crack growth in plate structures with ultrasonic guided waves

Abstract: Fatigue crack growth in plate structures is monitored with ultrasonic guided waves generated from piezoelectric transducers. Cracks initiate in the vicinity of fastener holes due to cyclic in-plane...