Enhancing the Strengths of Adhesion Bonds Between Composite Surface and Coating via UV Treatments

Field of composites is rapidly growing in many industries such as aviation, energy and automotive industries. Composites are known to have a high strength to low weight ratio. Significant improvement in the performance of coatings used in the protection of military and civil aircraft has been achieved the last thirty years. Composite coatings are exposed to many environmental conditions, which can significantly affect their properties. In this research, UV light treatment on the surface of composite was introduced to examine its effects on the adhesion properties between the coating and substrate. A cross-cut test was conducted on the composite panels to assess the adhesion of paint to the substrate after the treatments. Coating performance analyses were also carried out using a Fourier transform infrared spectrometer, water contact angle, and optical microscopic images. The first set of panels was treated with UV radiation for 0, 2, 4 and, 8 days, and the surface wettability was also assessed using the contact angle test. Two coats of paints, including a primer and top coat, were used, and the panels were exposed to UV radiation and immersed in water for 500 hrs and 1000 hrs. It was found that untreated panels showed a much higher contact angle of 106°, whereas the contact angle of panels treated with UV radiation was reduced to 47°. The cross-cut tests showed considerable flaking of the coating along the edges and squares of panels that were not treated, and very small flakes along the edges and parts of the grid square on panels that were UV treated, thus confirming the enhancement of coating adhesion between composite and coating surfaces by UV treatments.

A Study on Adhesively Bonded Aluminum Plates Under Shock-Wave Loading

Adhesive joint technology has been developed gradually, and the application fields of this type of joints have been expanded increasingly since they reduce the weight of the applications, provide uniform stress distribution across the joints, allow to bond similar, and dissimilar materials, and contribute to dampen the shock, and vibration. However, the performance of the adhesive joints under high loading rate such as blast or ballistic loading has been studied by few researchers. In this study, fully laminated plates consisting of 6061 aluminum plates (15” in diameter and 1/16” thick) and FM300K epoxy film adhesive were tested under shock wave loading. Full displacement field over the testing plates were obtained by TRC-SDIC technique, and the strain on the plates were computed by classical plate theory for large deflections. FEM model was analyzed and the results were compared with experimental results.

Design and Evaluation of Automated Robotic Ultrasonic Guided Wave Based Inspection System

This paper discusses the development and testing of an automated robotic ultrasonic guided wave based inspection system developed to provide an efficient, accurate and reliable method for performing nondestructive evaluation and longer term structural health monitoring in advanced composite structures. The development process and challenges in the design of the automated robotic system are described. A number of tests were performed using the developed robotic ultrasonic inspection system on composite honeycomb core sandwich materials. Experiments showed that the developed automated ultrasonic guided wave inspection system was successful at locating disbonds between the core and the facesheets. Environmental sensitivity testing was also performed to characterize the effect of changing temperature and humidity on system performance. These tests indicate that approach was relatively insensitive to environmental changes, so that this approach could be used in service environment without a significant reduction in performance. Current system testing indicates that the described robotic ultrasonic inspection approach offers an accurate and robust method for inspection and long term tracking of advanced structural system health.

Effect of Design Parameters on Lubrication Behavior of Spur Gear Pairs

An involute spur gear pair meshing model is firstly provided in this study to achieve relevant data such as rolling velocity, sliding velocity, curvature radius etc. These data are needed in a transient, Newtonian elastohydrodynamic lubrication (EHL) model which is provided later. Based on these two models, the behavior of an engaged spur gear pair during the meshing process is investigated under dynamic conditions, film thickness, pressure, friction coefficient etc. could be achieved through the models. Then, power loss under certain operating condition is calculated. Relationship between power loss and lubrication performance is also analyzed.

Sensing Artificial Hole and Crack in Carbon Nanotube Enhanced Glass-Fiber Reinforced Composite Panel

Glass fabric epoxy resin based composite panels enhanced with carbon nanotubes were subjected to damage while changes in electrical resistance were obtained via embedded electrodes. The purpose of the study was to develop an alternative method to Electrical Impedance Tomography (EIT), which generates conductivity field, hence, indicating presence of various damages. The current method provides damage field by taking meticulous measurements of electrical resistance of panel. The method does not monitor conductivity as in the EIT but utilizes electrical resistance changes to detect damage. In the current form, it employs a network of 64 (8 × 8 grid) electrodes distributed evenly in a typical panel instead of the boundary electrodes used in EIT. Even though 64 electrodes were employed, fewer electrodes were sufficient to produce accurate indication of damage location and its size. In previous studies percolation threshold for carbon nanotube-epoxy mixture was determined, which enabled selection of optimal CNT concentration used in manufacturing of glass fiber reinforced panels. The glass fiber reinforced panels were manufactured by vacuum infusion method. The typical panel consisted of 10 glass fabric (S-2) plies. Copper electrodes were embedded beneath the top layer fabric ply. Electrical resistances measurements were obtained using four-probe technique. In the four-probe method, two outer electrodes are used to source a known current through the panel, while the two inner electrodes provide voltage drop needed to compute resistance. The technique minimizes contact resistance between electrodes and the composite, which could be order of magnitude larger than the material resistance being measured. Electrical resistance of cured glass fiber reinforced CNT-epoxy panels was first measured without any damage. Afterwards, damages in form of circular hole were inflicted to the panel starting with 1/8” diameter and enlarging it to 1/2” in steps of 1/8”. After the largest hole, 0.04” (∼1 mm) width cracks emanating from the hole were inflicted. During all measurements, electrical current passing through the source and sink electrodes was kept constant and changes in voltage from the inner probes were recorded. The thrust of the method is to incorporate a curve fit for quantifying the changes in resistance. The method can be applied to damage quantification in panels. The smaller spaced electrode distribution was more sensitive to smaller damages as expected, but the larger spaced electrodes network was sufficiently responsive to smallest damage. Experimental results were fairly good at predicting the damage and its magnitude. Results also indicated a very good agreement with the finite element simulations of the panels. Application of this technique can be a powerful tool for real time structural health monitoring of manufactured composites.

Impact Localization on a Composite Plate With Unknown Material Properties Using PWAS Transducers and Wavelet Transform

In this work, an impact experiment on a composite plate with unknown material properties (its group velocity profile is unknown) is implemented to localize the impact points. A pencil lead break is used to generate acoustic emission (AE) signals which are acquired by six piezoelectric wafer active sensors (PWAS). These sensors are distributed with a particular configuration in two clusters on the plate. The time of flight (TOF) of acquired signals is estimated at the starting points of these signals. The continuous wavelet transform (CWT) of received signals are calculated with AGU Vallen wavelet program to get the accurate values of the TOF of these signals. Two methods are used for determining the coordinates of impact points (localization the impact point). The first method is the new technique (method 1) by Kundu. This technique has two linear equations with two unknowns (the coordinate of AE source point). The second method is the nonlinear algorithm (method 2). This algorithm has a set of six nonlinear equations with five unknowns. Two MATLAB codes are implemented separately to solve the linear and nonlinear equations. The results show good indications for the location of impact points in both methods. The location errors of calculated impact points are divided by constant distance to get independent percentage errors with the site of the coordinate.

Full Frontal Crashworthiness of Carbon Fiber Composite Front Bumper Crush Can (FBCC) Structures

This research study highlights the testing method and relevant results for assessing impact performance of a carbon fiber composite front bumper crush can (FBCC) assembly subjected to full frontal crash loading. It becomes extremely important to study the behavior of lightweight composite components under a crash scenario in order to apply them to automotive structures to reduce the overall weight of the vehicle. Computer-aided engineering (CAE) models are extremely important tools to virtually validate the physical testing by assessing the performances of these structures. Due to lack of available studies on carbon fiber composite FBCCs assemblies under the frontal crash scenario, a new component-level test approach would provide assistance to CAE models and better correlation between results can be made. In this study, all the tests were performed by utilizing a sled-on-sled testing method. An extreme care was taken to ensure that there is no bottoming-out force for this type of test while adjusting the impact speed of sled. Full frontal tests on FBCC structures were conducted by utilizing five high-speed cameras (HSCs), several accelerometers and a load wall. Excellent correlation was achieved between video tracking and accelerometers results for time histories of displacement and velocity. The standard deviation and coefficient of variance for the energy absorbed were very low suggesting the repeatability of the full frontal tests. The impact histories of FBCC specimens were consistent and in excellent agreement with respect to each other. Post-impact photographs showed the consistent crushing of composite crush cans and breakage of the bumper beam from middle due to the production of tensile stresses stretched caused by straightening of the bumper curvature after hitting the load wall.

Peridynamics Using Irregular Domain Discretization With MOOSE-Based Implementation

In this paper, reformulation of classical bond-based peridynamic thermomechanical model for irregular domain decomposition and its MOOSE-based implicit formulation are presented. First, the irregular grid based peridynamic thermomechanical model is formulated and model parameters are derived. Following this, an implicit formulation for the solution of static or quasi-static problems is presented. Some aspects of the MOOSE-based implementation are given. After that, the formulation is verified against benchmark solutions for thermomechanic problems. Crack initiation and propagation in circular (2D) and cylindrical (3D) nuclear fuels at high temperature are studied using irregular grids.

Tunable Triangular Cellular Structures by Pneumatic Control of Dual Channel Actuators

Programmable matter, a material whose properties can be programmed to achieve desired density with volume change, shapes or structural properties (stiffness, strength, Poisson’s ratio, etc.) upon command, is an important technology for intelligent materials. Recently emerging soft robotics-based pneumatic control can be potentially used for the design of programmable matter due to its several advantages — quick response for actuation, stiffening effect with internal air pressure, easy to manufacture, inexpensive materials, etc. The objective of this work is to construct programmable two-dimensional (2D) cellular structures with pneumatic actuators, investigating the effect of local deformation of the pneumatic actuators on the macroscopic pattern generation and mechanical properties of cellular structures. We synthesize 2D soft triangular structures with pneumatic actuators embedding dual air channels wrapped with fiber reinforcement. The local deformation modes provide different macroscopic deformations of cellular structures. We build an analytical model integrating the deformation of a single actuating member with nonlinear deformation of cellular structures. Finite element based simulations and experimental validation are followed. This study integrates soft robotics with cellular structures for intelligent materials design, expanding the design space of materials with programming. The fast response of the tunable soft cellular structures may be an ideal for the application of acoustic metamaterials with tunable band gaps.

The Effect of a Quarter-Circle Corner Crack on the Distribution of the SIF Along the Front of a Non-Aligned Semi-Elliptical Surface Crack in an Infinitely Large Plate Under Uniaxial Tension

The evaluation of the mutual effect of non-aligned multiple cracks is a prerequisite in applying fitness-for-service codes. For non-aligned parallel cracks, during on-site inspection, one needs to decide whether the cracks should be treated as coalesced or separate multiple cracks for Fitness-for-Service. In the existing literature, criteria and standards for the adjustment of multiple nonaligned cracks are very source dependent, and those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the authors previously reported on the influence of an embedded crack on an edge crack in 2-D scenarios and, more recently, in 3-D scenarios of the influence of a surface crack on a quarter-circle corner crack. However, realistic crack configurations detected using non-destructive methods are generally 3-D in nature and their influences are mutual. Thus the SIF distribution characteristics along the surface crack is equally important as the SIF distribution of the corner crack when Fitness-for-Service rules are to be applied. Therefore, non-aligned flaws with different configurations and shapes and the SIFs along their crack fronts are deemed necessary in order to obtain more practical guidance in the usage of rules speculated in Fitness-for-Service codes. In this study, the characteristics of the SIF distribution along a semi-elliptic non-aligned surface crack is examined under the influence of a quarter-circle corner crack of various geometries in an infinitely large plate. For any given geometry of a quarter-circle corner crack, a pair of horizontal (H) and vertical (S) separation distances between the two cracks is chosen followed by a detailed analysis of the effect of the quarter-circle corner crack on the 3D SIFs of the surface crack at different ellipticities. The analysis is repeated for various combinations of separation distances S and H. The results from this study are collectively significant to the understanding of the correlation between the criteria and standards in Fitness-for-Service community and the consequence of their usage in engineering practice.