Papers by Keyword: Non-Destructive Evaluation (NDE)

Abstract: This paper demonstrates a unique application of DIC wherein the structural performance and structural integrity have been evaluated together almost in real-time. The results obtained from the ground level tests, simulating the bonding between the TPS to the base structure of a space crew module, are reported to find the adequacy of two different adhesives prior to actual bonding. The test objective was to characterize the adhesives based on the structural performance (deflection and strain behavior) of the TPS and conduct health monitoring in real-time (i.e. abort the test whenever the TPS fails). The dual objective could be met using DIC in a full-field and non-contact manner, which was essential due to the limitations of the contacting type measurements.

Abstract: In this research, the correlations between the magnetic signals and the mechanical behavior of a ferromagnetic steel structure under tensile loads were investigated. The failure mode of the tested steel joint was the buckling of the annular plate. It was observed that during the loading process the piezomagnetic response demonstrated a different behavior compared to the mechanical response. The greater variation of the load-B field curve shows that piezomagnetic signal is a more sensitive indicator of structural failure than the mechanical response. The piezomagnetic effect may be used as a promising method to monitor the failure process of civil infrastructures.

Abstract: A study has been carried out to characterize the effect of variation of processing parameters on the phase contrast data between defective and defect-free areas obtained through the use of pulse phase thermography (PPT). Processing parameters used to implement the fast Fourier transform (FFT) have been varied. Phase contrast was maximized when the datum used as the start point for the FFT was taken as the frame just after the pulse. Optimum recording duration was found when the surface temperature had returned to its initial temperature. A truncation shorter than this resulted in a reduced phase contrast. Sampling interval and range is required to be balanced against the quantity of data produced and the computational expense. A sampling frequency of 0.06 Hz was suggested for the sample studied as this allowed peak phase contrast to be captured without unnecessarily increasing data size. Repeatability of tests was also investigated. It was found that PPT phase contrast results have been found to be repeatable with a maximum standard deviation of 6°.

Abstract: Considering the damage that composite material under loading may occur, acoustic emission (AE) technique is adopted to perform non-destructive evaluation (NDE). In order to obtain the acoustic emission emitted from the composite material, a novel fiber optic AE sensor which is based on single mode fiber optical fused-tapered coupler design is developed. Futhermore, its fabrication process was described and performance was studied. Results of a pencil break test on the composite laminate show that the fiber optic AE sensor have better frequency response than the commercial piezoelectric sensor. During a tension experiment of a carbon fiber composite specimen , the fiber optic sensor which was mounted on it detected the enormous acoustic emission signals. To analyze their characteristic parameter, such as amplitude, duration, can identify the type of failure to composite materials, including Matrix cracking , Interface stripping, fiber breakage. Experimental results would offer the reference to damage identification to complicate composite structures.

Abstract: An apparatus for in situ measuring the hysteresis of magnetic materials by using pulsed magnetic field is structured. The samples were locally magnetized to saturation by the pulsed magnetic field. The pulsed field is generated by the discharge of a capacitor over the magnetizing coil. The measurement has been developed in LabView environment using National Instrument Data Acquisition Cards. The hysteresis loops of Q235 steel samples under various compressive stresses are presented.

Abstract: The fatigue crack growth experiment was carried out at room temperature for the standard SEB(3) specimens of 40Cr steel, the distribution of the surface magnetic field of the specimen under same load and different cycle numbers (N) was studied. By analyzing relations between the magnetic signals and the crack propagation life, a new damage parameter model has been established by magnetic signals. According to this model, we can evaluate the residual life of ferromagnetic components excellently. This belong to basic research on early damage inspecting and residual life assessment for ferromagnetic materials, it confirmed that residual life assessment and safety estimating for ferromagnetic components based on metal magnetic memory technology is feasible.

Abstract: There has been a growing interest in the use of composites especially in structural application ranging from aerospace to automotive and marine sectors. However, their performances under impact loading represent one of the major concerns as impacts may occur during manufacture, normal operations and maintenance. This paper presents two novel NDT techniques, thermosonics and digital shearography (DISH) to detect and assess barely visible impact damage (BVID) produced on a stiffened composite wing panel by unknown low energy impacts. Thermosonics is based on synchronized infrared imaging and ultrasonic excitation. Despite the apparent simplicity of the experimental setup, thermosonics involves a number of factors, e.g. acoustic horn location, horn crack proximity, horn-sample coupling etc., that significantly tend to influence both the degree and the period of the excitation. Then, a numerical-experimental procedure for the assessment of the size and depth of delamination by digital shearography (DISH) is proposed. The flaw detection capabilities of DISH have been evaluated by measuring the dynamic response of the delaminated area to applied stresses. The shearographic methodology is based on the recognition of the (0 1) resonance mode per defect. A simplified model of thin circular plate, idealized above each impacted area, is used to calculate the natural frequency of vibrating delamination. The numerical difference between experimental resonance frequencies and those computationally obtained is minimized using an unconstrained optimization algorithm in order to calculate the delamination depth. The results showed that thermosonics is a quick and effective method to detect and localize BVID damage while the combined shearography and optimization methodology was able to size and localize delamination due to low velocity impacts.

Abstract: The thermoelastic response obtained from an infra-red (IR) detector contains two components: the magnitude of the small stress induced temperature change caused by the thermoelastic effect and the phase angle of the temperature change relative to a reference signal generated by an application of a stress change. The phase angle is related to nonlinearity in the thermoelastic response and departures from the simple linear relationship that underpins thermoelastic stress analysis (TSA). The phase data could be used to make an assessment of temperature evolutions caused by viscoelastic behaviour resulting from damage and provide a basis for its evaluation. In the current paper the physics of other infra-red techniques used for non-destructive evaluation is used to better understand the nature of the thermoelastic response. The objective is to provide better exploitation of TSA by alternative processing of the IR measurements. Three case studies are presented that demonstrate the potential of the alternative processing for evaluating damage.

Abstract: This paper presents an experimental investigation of a new method for damage detection based on the most fundamental concept in continuum mechanics: strain compatibility. Compliance with this principle implies a deformed material is free from discontinuities, which are indicative of many types of structural damage. Therefore the principle of strain compatibility, in its ability to identify discontinuities, is very promising as a new foundation for future research into non-destructive evaluation and structural health monitoring technologies. The proposed method has many advantages compared to existing damage detection techniques, such as its invariance to material properties, type and intensity of loading, and the geometry of the structure. In this paper, a proposed formulation of the strain compatibility equation for beam structures, which is invariant to loading intensity, is presented. An experimental investigation of the proposed algorithm was conducted on a delaminated cantilever beam, utilising a PSV-3D scanning laser vibrometer. The experiment demonstrated that the strain compatibility technique can accurately locate delamination damage in composite beam structures.

Abstract: Thermal barrier coatings (TBCs), which comprise metallic and ceramic multilayers, have been widely used in the hot section of aeroturbine engines to increase turbine efficiency and to extend the life of metallic components. An improvement in TBCs requires a better understanding of the complex changes in their structure and properties that occur under harsh operating conditions that eventually lead to their failure. In this paper, the developments of TBCs over the past 30 years are briefly reviewed. A description of materials issues involved in the state-of-art and next generation TBCs systems is presented, together with a summary of the current understanding of failure mechanisms; highlighting the challenges and prospects in TBCs research.