Mechanical Engineering

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https://hdl.handle.net/10323/11894

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Amplitude Method to Detect Debonding for Stack Bond Adhesive
(2024-01-01) Huang, Xiabao; Barber, Gary; Gu, Randy; Wang, Xia; Latcha, Michael; Qu, Hongwei; Zhou, Jun
Adhesively bonded joints have been applied in the automotive industry for the past few decades due to their advantages such as higher fatigue resistance, light weight, capability of joining dissimilar materials, good energy absorption and high torsional stiffness for overall body structure. They also provide an effective seal against noise and vibration at a low cost. There exists the challenge of defining the fatigue characteristics of adhesive joints under cyclic loading conditions and conventional methods have limitations in detecting the crack initiation of a bonded joint. This study introduces a method of detecting crack initiation by using the frequency method. It is found that stiffness change in the system is highly correlated to change in natural frequencies. By monitoring the change in natural frequencies, the crack initiation can be detected.
Development of Digital Shearography for Complex Defects Inspection
(2021-11-09) Zhang, Boyang; Yang, Lianxiang; Barber, Gary; Qu, Hongwei; Narainen, Roderigue
Digital shearography measures the first derivative of the object surface deformation, which has the advantages of high sensitivity, full field, non-contact, realtime and anti-disturbance. It is widely used in materials inspection in industry. The information acquisition methods of the first derivative distribution are mainly divided into the intensity method and the phase shift method. The intensity method is to directly obtain the first derivative phase distribution by subtracting the light intensity map. The phase shift method to obtain phase information can be divided into temporal phase shift and spatial phase shift. Most digital shearography systems are single camera based and can only capture one image every shoot. However, unpredictable defects like the narrow crack and minor flaws could induce incomplete detection due to some limitations. There are two major issues on the measurement, one is the defect with the irregular shape which is not sensitive to the digital shearography, another is the deformation made of defects that is much smaller than the resolution of cameras. Digital Shearography measures the first derivative of deformation on the object surface because the shearing direction determines the derivative direction being measured, tests using multiple shearing directions are sometimes required to detect all kinds of defects. When the deformation is long and narrow as a crack while the shearing direction is perpendicular to the crack growing direction, digital shearography has the best sensitivity. In opposite, if the crack growing direction is parallel to the shearing direction, digital shearography is not able to find it out. Irregular shape defects detection is a tough challenge for digital shearography. Another challenge is the defects that are too small for the field of view. The limited pixels can miss the defects due to the low signal to noise ratio. To increase the sensitivity of detecting minor defects, a small field of view measurement is needed but it is time consuming in a large surface area inspection. The new development can be divided into three categories: 1) Modified Michelson interferometer based dual shearing digital shearography. 2) Spatial light modulator based dual shearing direction shearography. 3) Polarized digital shearography for simultaneous dual sensitive measurement. The basic theory, optical path analysis, preliminary studies, results analysis and research plan are shown in detail in this dissertation.
Digital Shearography for Nondestructive Testing (NDT): Determination of Smallest Detectable Defect and Improvement of its Visibility
(2024-01-01) Guo, Bicheng; Yang, Lianxiang; Barber, Gary; Romagnoli, Marco Gerini; Lin, Hejie; Lu, Lunjin
Sensitivity is a key parameter for using NDT technology. Determining what factors affect the sensitivity of NDT and establishing the model to facilitate engineers to select the appropriate system parameters and the loading magnitude are very important in the practical applications. In the past decade, Digital shearography has been widely used as a NDT tool for detecting delaminations and debonding defects in various composite materials, such as glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP), Honeycomb structures, etc. Digital shearography is a laser interferometric technique and able to measure the first derivatives of deformation, i.e. strain information. It is suited well for NDT because defects generate strain concentration after a loading. As an NDT method, the sensitivity of digital shearography is an important parameter to measure the technology’s defect detection capabilities. However, due to various limitations, the sensitivity research of digital shearography is still in its infancy. First, this technique lacks a numerical model to offer a theoretical foundation for determining the minimum detectable delamination/debonding limits and the detectable depth of defects. Secondly, because a shearogram is a fringe pattern which is composed of both global deformation and defect information. smaller defect information is easily lost in the fringe patterns from global deformation. This research conducts in-depth study around determining the sensitivity of digital shearography and improving the defect visibility to meet the practical needs of helping engineers quickly select loads and quickly identify defects. To solve these problems, the main research work and innovation results are as follows: (1)In response to the first problem, this research presents a methodology of digital shearography for determining the size of the smallest detectable defect and its depth under various loading magnitudes for the purpose of nondestructive testing. First, a mechanical model based on the thin plate theory to calculate the expected bending of close-to-surface defects was proposed; the model built a relationship among the deformation caused by a defect, the size and the depth of the defect, as well as the load and the material properties. Second, the relationship between the relative deformation measured by shearography and the deformation induced by a defect was established based on the optimized shearing amount and the sensitivity of digital shearography. Based on these analyses, relationships between the size of the smallest detectable defect and the depth under different load amounts were established for different defect shapes. (2)A demonstration of the sensitivity limit of digital shearography is shown on the basis of the sensitivity model, and the search for strategies to improve digital shearography is undertaken. After research, while keeping the equipment consistent, the material unchanged, and the loading conditions the same, the best way to improve the sensitivity of digital shearography is to increase the contrast between defect information and background information. This method can make defects information clearer. Based on that, the second purpose was to examine methods for improving sensitivity found in previous studies and to discuss the advantages and disadvantages of all methods and developed the segment fitting method. According to the previous discussion, it can be found that the most common method is to make a fitting plane to represent the global deformation by unwrapping fringe pattern to build the continuous shearogram, and then subtracting the plane to increase the contrast. Secondly, the continuous shearogram of complex deformations makes it challenging to choose the fitting equation. Based on this, a piecewise fitting method is proposed. This method is based on the conventional fitting method, which is fitted based on the phase change between each fringes on the shearogram. Because the phase values between each fringe are linearly distributed, this method does need to consider the fitting equation selection. The new planes then need to be subtracted from the original image to remove the global deformation, thus preserving the defect. (3)The second innovation of this research is the development of a practical and effective method to experimentally removes fringe patterns caused by the global deformation that makes small defects directly visible, which improves the non-destructive testing capabilities of digital shearography, thereby simplifying defect detection and visualization. For shearographic Non-Destructive Testing (NDT), the phase distributions of two interferogram under different loads P1 and P2 are recorded. This novel approach involves recording one additional phase distribution of an interferogram at a load between P1 and P2, e.g. P1’. Two phase maps of shearograms can be generated, corresponding to the two loads 2 = (P1’-P1) and 1 = (P2-P1), respectively. Because of the nondestructive nature of the testing, the magnitude of the loads P1 and P2 is small, and the 1st derivative of global deformation of the test part is assumed to be linear. Therefore, a linear coefficient C based on the two shearograms can be determined. The information from global deformation is then removed by subtracting the shearogram generated with the small load 2 multiplied by the correlation coefficient C from the one obtained with the relatively large load 1. This technique is further improved by calculating a complete surface linear coefficient Cij, which improves the detail processing of the deformation of samples with complex geometry and mechanical properties. Experimental verification was conducted based on specimens with prefabricated defects of different sizes and different loading conditions to verify the proposed mathematical model and experimental methods to eliminate global deformation. Experimental results show that the developed model can provide useful estimates for digital shearography NDT, and in particular can help test engineers estimate the size of the smallest detectable defect and the depth of the defect under corresponding load magnitude. Also, the experimental coefficient method can effectively evaluate a variety of structures and also be verified to remove global deformation, which improves defect detection capabilities and increases visualization of the digital shearography.
Molecular Dynamics Simulation of the Effect of Particle Hardness on Tribological Properties of Nanofluids
(2022-01-01) Xu, Cang; Barber, Gary; Schall, James; Yang, Ankun; QAu, Hongwei; Zhao, Peng
The determination of physical properties of nanofluids is mature, but the knowledge of tribological properties of nanofluids is limited. In this paper, the effects of surface roughness, fluid thickness, nanoparticle hardness, and number of nanoparticles on friction are explored systematical using a 2D Lennard-Jones molecular dynamics model. LJ parameters were chosen such that the ratio of stiffness of the nanoparticles to the opposing surfaces was approximately equal to ratio of stiffness of either aluminum oxide or zinc oxide to steel. A total of two hundred and twenty configurations were investigated. The results show that the benefits or drawbacks of nanofluid lubricants are sensitive to the friction regime (boundary, mixed, or hydrodynamic). When nanoparticles are present in lubricant-starved boundary conditions (fluid thickness less than the surface roughness amplitude), nanoparticles offer support that keeps the opposing surfaces separated. This separation results in reduced contact between the opposing surfaces and provides surface smoothing, which in turn lowers friction relative to the base fluid. At intermediate levels of fluid thickness where the fluid thickness and roughness are approximately equal, the presence of nanoparticles has a detrimental effect on friction. Nanoparticles jam and lock surfaces together and increase friction relative to the base fluid. As fluid thickness increases, the friction of the nanofluid generally remains higher than the base fluid likely due to the increased viscosity of fluid due to the presence of the nanoparticles. This work suggests nanofluids may offer limited benefits under specific lubrication conditions, but are detrimental under most conditions.
Self-Crack Healing of Engineering Ceramics
(2022-03-21) Hammood, Israa Arif; Barber, Gary; Adams, Robert; Schall, J Dave; Debnath, Debatosh; Yang, Ankun; Zaidan, Shihab
The purpose in its simplicity is to heal the damage in a sample composed of ceramic particles through the heat treatment or through applying another source to heal the damage might be through using a laser source at room temperature to reduce the cost of wasting efforts and materials. The system can be designed to include a sensor to sense the damage in the component and a healing agent like loose particles or a specific source that provides an immediate treatment through the heating in order to create or generate the glassy phase. Self-crack-healing materials are able to sense the crack and heal it. The notion of not giving up on things can be considered as the motive for such type of research. Most ceramics are brittle and hence they are sensitive to flaws and cracks. Ceramics are subjected to thermal and mechanical stresses during service. Residual stresses may eventually cause microcracks (internal and surface cracks) and the failure of the component in use. This limits their use as structural engineering materials, and thus applying or inducing a self-crack healing ability would be a solution to overcome this problem. Great benefits can be expected from the components in use while applying the self-healing ability, such as reducing maintenance, inspection, and the cost of machining and polishing as well, which enhances the reliability of the component in use, and hence achieving a higher structural integrity*. Developing new materials with increasing resistance to wear and corrosion is the goal for many researchers and manufacturers as well. Consequently, an attempt to imitate the mechanisms employed by nature through the biological systems have been made to design self-healing materials and coatings for corrosion protection which can result in complete recovery*. Ceramics can be used in many applications including aeroengine turbine blades, gas turbine blades, high performance bearings and many other applications that require high temperature service *. However, these ceramics have low fracture toughness, which means that they are brittle and sensitive to flaws such as micro and macro cracks, which limit their applications as structural components. The present research is focused on the self-crack healing ability of Spinel nanocomposites and SiC bonded Kaolinite. The self-crack healing behavior was investigated as a function of the healing conditions (time, temperature, and chemical composition) as well as the mechanism responsible for healing the cracks.
Tin Whiskers Mitigation by Co-electroplating Antimony
(2024-01-01) Zhang, Lei; Wang, Xia; Barber, Gary; Yang, Ankun
Electroplating Sn coatings are used extensively in the electronics industry because of their excellent solderability, ductility, electrical conductivity, and corrosion resistance. However, tin whiskers have been observed to grow spontaneously from the electroplating tin coatings for over 70 years. This filament-type structure can lead to short circuits and device failures by bridging adjacent electronics. Over the last several decades, adding a small amount of lead (Pb) has been the most widely adopted method for mitigating Sn whiskers growth. However, this 70-year-old issue of whisker growth has reemerged due to the ban on the use of Pb from Sn-based plating and solders enforced by the European legislation on Restriction of Hazardous Substances (RoHS).

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