Mohammad Albakri

• Professor (Assistant) at Tennessee Technological University

Counterfeiting is a significant problem for safety-critical systems, since cyber-information, such as a quality control certification, may be passed off with a flawed counterfeit part. Safety-critical systems, such as planes, are at risk because cyber-information cannot be provably tied to a specific physical part instance (e.g., impeller). This pa...

Structure-Borne Traveling Waves (SBTWs) have significant promise as a means of underwater propulsion, solid-state motion, and drag reduction. However, there is limited understanding over how to tailor SBTWs for these applications. This study establishes guidelines and a procedure for tailoring SBTWs on thin-walled two-dimensional (2D) surfaces. The...

Structure-Borne Traveling Waves (SBTWs) have significant promise as a means of underwater propulsion, drag reduction, and solid-state motion. However, there is poor understanding of how to tailor SBTWs favorable for these applications. This study establishes guidelines and a straight-forward method for generating favorable SBTWs on two-dimensional...

Motivated by its success as a structural health monitoring solution, electromechanical impedance measurements have been utilized as a means for non-destructive evaluation of conventionally and additively manufactured parts. In this process, piezoelectric transducers are either directly embedded in the part under test or bonded to its surface. While...

Driven by the need for describing and understanding wave propagation in structural materials and components, several analytical, numerical, and experimental techniques have been developed to obtain dispersion curves. Accurate characterization of the structure (waveguide) under test is needed for analytical and numerical approaches. Experimental app...

Structure-Borne Traveling Waves (SBTWs) have significant potential as a means of underwater propulsion and drag reduction, but there is limited understanding of how to tailor SBTWs, especially on the two-dimensional (2D) surfaces needed for these applications. To tailor SBTWs on 2D surfaces they must propagate in defined directions and have control...

Driven by the need for describing and understanding wave propagation in structural materials and components, several analytical, numerical, and experimental techniques have been developed to obtain dispersion curves. Accurate characterization of the structure (waveguide) under test is needed for analytical and numerical approaches. Experimental app...

In this paper, the authors explore the use of impedance-based monitoring techniques for in-situ detection of additive manufacturing build defects. By physically coupling a piezoceramic (PZT) sensor to the part being fabricated, the measured electrical impedance of the PZT can be directly linked to the mechanical impedance of the part. It is hypothe...

The rise of the interconnected manufacturing enterprise has extended its vulnerability space to malicious cyber-physical attacks. To improve the resilience of a manufacturing enterprise to cyber-to-physical attacks, a robust set of quality tools for part and process authentication and verification are needed. However, current Non-Destructive Evalua...

The acoustoelastic theory has been widely utilized for nondestructive stress measurements in structural components. Most of the currently available techniques operate at the high-frequency, weakly-dispersive portions of the dispersion curves and rely on time-of-flight measurements to quantify the effects of stress state on wave speed. High-frequenc...

Elastic meta-structures, with wave propagation control capabilities, have been widely investigated for mechanical vibrations suppression and acoustics attenuation applications. Periodic architected lattices, combined with mechanical or electromechanical resonators, are utilized to form frequency bands over which the propagation of elastic waves is...

Dispersion relations describe the frequency-dependent nature of elastic waves propagating in structures. Experimental determination of dispersion relations of structural components, such as the floor of a building, can be a tedious task, due to material inhomogeneity, complex boundary conditions, and the physical dimensions of the structure under t...

An algorithm is introduced to solve the general multilateration (source localization) problem in a dispersive waveguide. The algorithm is designed with the intention of localizing impact forces in a dispersive floor, and can potentially be used to localize and track occupants in a building using vibration sensors connected to the lower surface of t...

Current acoustoelastic-based stress measurement techniques operate at the high-frequency, weakly-dispersive portions of the dispersion curves. The weak dispersive effects at such high frequencies allow the utilization of time-of-flight measurements to quantify the effects of stress on wave speed. However, this comes at the cost of lower sensitivity...

The flexibility offered by additive manufacturing (AM) technologies to fabricate complex geometries poses several challenges to non-destructive evaluation (NDE) and quality control (QC) techniques. Existing NDE and QC techniques are not optimized for AM processes, materials, or parts. Such lack of reliable means to verify and qualify AM parts is a...

Purpose This work proposes the utilization of electromechanical impedance measurements as a means of non-destructive evaluation (NDE) for additive manufacturing (AM). The effectiveness and sensitivity of the technique for a variety of defect types commonly encountered in AM are investigated. Design/methodology/approach To evaluate the feasibilit...

A finite element (FE) model simulates an unconstrained aluminum thin plate to which four macro-fiber composites are bonded. This plate model is experimentally validated for single and multiple inputs. While a single input excitation results in the frequency response functions and operational deflection shapes, two input excitations under prescribed...

The present work explores the generation of two-dimensional steady-state flexural waves that are non-reflective on a thin rectangular plate with free boundary conditions when excited by two macro-fiber composites (MFCs). The voltage signals to the MFCs have a frequency lying halfway between two adjacent resonant frequencies with a phase difference...

Embedded and surface bonded piezoelectric wafers have been widely used for control and monitoring purposes. Several nondestructive evaluation and structural health monitoring techniques, such as electromechanical impedance and wave propagation–based techniques, utilize piezoelectric wafers in either active or passive manner to interrogate the host...

The high-frequency nature of impedance-based structural health monitoring makes the utilization of impedance signature for model-based damage characterization a challenging problem. In this study, a novel damage characterization approach that utilizes impedance signature measured with a single piezoelectric wafer is developed. Length-varying spectr...

The acoustoelastic theory has been widely utilized for nondestructive stress measurement in structural components. Most of the currently available techniques operate at the high-frequency, weakly-dispersive portions of the dispersion curves, and rely on time-of-flight measurements to quantify the effects of stress state on wave speed. This adversel...

The focus of this study is to understand traveling wave generation and propagation in reduced order 2D plate models. A plate with all clamped (C-C-C-C) boundary conditions was selected to be the medium through which the wave propagation occurs. The plate is excited at multiple locations by point forces which generates controlled oscillations result...

Impedance-based structural health monitoring (SHM) is a non-destructive, active technique for real-time structural damage assessment. Conventional impedance-based SHM practices apply a sinusoidal signal of fixed amplitude to excite the piezoceramic patch and obtain the impedance signature over a certain frequency range. Damage is then detected by c...

Due to its simplicity, impedance-based structural health monitoring (SHM) has gained a lot of interest in the SHM community. Impedance measurements have proved to be very effective in detecting the presence of damage. Damage identification, on the other hand, can hardly be done with a single impedance measurement, and an array of sensors is normall...

Friction stir process (FSP) is a severe plastic deformation based secondary processing technique that can be utilized to engineer novel microstructures in metallic alloys. It is well known that such techniques are cumbersome and require significant experimental work and material to determine optimum processing conditions. Therefore in this work, we...

Forming of light-weight highly stiff aluminium foam sandwich (AFS) panels into complex 3D components would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using numerical simulations. Deformation behaviour of AFS panels is studied during high-temperature...

Superplastic forming technique provides a unique solution for meeting the growing demand on light-weight materials for transportation applications. However, being a rate controlled process, confined to low strain rates, makes it relatively slow and unfavorable for mass production applications. In this paper, an optimal variable strain rate forming...

Proton Exchange Membrane Fuel Cells (PEMFC’s) are a promising technology in the field of clean energy. Bipolar plates are the main components of the PEMFC as they contribute to about 80% of their weight and affect their performance significantly. This study shows the effect of varying the cross sectional area of the flow channel in the bipolar plat...

This paper studies the effects of the interfacial friction distribution on the integrity of superplastic formed parts. For that purpose, the deformation of an AA5083 superplastic aluminum alloy into a long rectangular box is investigated. The die surface is divided into five regions for local application of constant friction coefficients. The comme...

In this article an educational embedded mechatronic system based on the MATLAB xPC target is presented. xPC target, a tool provided by MATLAB and its Simulink toolbox, offers a practical means for developing a hardware-in-the-loop (HIL) simulation environment. Since ordinary personal computers (PCs) can be used for modeling, analysis, design, monit...