Creep life prediction is very important to maintain safe operation of thermal power plants for a long-term period. In this study, an alternative creep life prediction method was proposed based on a relationship between creep exponent n and creep coefficient k. A high temperature indentation creep test was conducted to identify the creep exponent and creep coefficient for each specimen with different creep damage ratio. Subsequently, the relationship between the creep coefficient and creep exponent for each creep damage ratio was focused on. As a result, it was confirmed that a new parameter B introduced based on both creep coefficient and creep exponent linearly increase as the creep damage ratio increases. Furthermore, the B is uniquely determined by the creep damage ratio regardless of the temperature and stress conditions. These results indicate that the creep life can be predicted with a high accuracy using the B.

This research focused on the assessment of the damaged area on aramid/epoxy composites subjected to high velocity impact. Digital X-ray radiography and active pulsed thermography techniques were used for performing post-mortem analysis of the impacted specimens (8 to 28 aramid layers). Two types of projectiles were used: 9 mm Luger FMJ and .357 Magnum FMJ. Dedicated algorithms were developed to post-process the thermograms obtained and the results are compared with the damaged diameter measured directly on the X-ray radiographs. The output of the three methods are therefore compared and discussed.

The effect of load interruptions on the fatigue behavior of (±45)_2S angle-ply glass/epoxy composite laminates was investigated in this work. Constant amplitude fatigue experiments were performed at different stress levels to derive base line fatigue data. In addition, interrupted-fatigue experiments were performed by removing the cyclic loading for two hours repetitively, after cycling for 20% of the fatigue life achieved under continuous loading at the same maximum cyclic stress level. The specimens loaded under interrupted fatigue exhibited longer fatigue live than those continuously loaded until failure.

This paper, prepared in the framework of the COST Action SARCOS WG2 activities (http://www.cost.eu/COST_Actions/ca/CA15202), provides an overview of the main concepts underlying the experimental characterization of the self-sealing capacity of cement-based materials. This effort intends to pave the way towards standardization of such experimental methods for a comparative assessment of the self-healing capacity of different cement-based materials and of the effectiveness of different techniques, in order to incorporate self-healing concepts and outcomes into durability-based predictive models and design approaches.

In this research, a feasibility study to measure a magnitude and a cycle of a time-varying stress of a specimen by a natural frequency was carried out. An experiment was conducted. We used a specimen of a round bar with 8 mm diameter and 290 mm span length which was fixed at both ends. A sinusoidal axial stress was applied to the bar. A deflection of the bar in a free vibration was measured by a laser beam displacement device. To collect much information on the deflection, a device which hit the bar periodically was made up. A fast Fourier transform method, a short-time Fourier transform method and a wavelet analysis were applied to the deflection. The methods give us relations among time, a frequency and a magnitude of a signal with complicated representations. Applying the analyses to the experimental data, we tried to evaluate a magnitude and a cycle of a time-varying load.

The paper firstly focuses on selected results obtained by continuously monitoring the dynamic response of three ancient masonry towers in Italy in order to highlight the possible effects of changing temperature on the resonant frequencies; subsequently, the removal of environmental effects (needed for an effective performance assessment and damage detection) is addressed and discussed using the data acquired on a challenging historic tower.

In active thermography the use of an optimised excitation source can simplify the 1
interpretation of measurement results. Our custom designed source, especially designed for dynamic 2
line scanning thermography, minimises the needed excitation power and the biasing side effects 3
generated by a wide-range heat source. The source is redesigned, starting from a regular heat source, 4
to focus the available energy such that the needed heating power is provided in a small band. Ray 5
tracing software is used to design absorbers and reflectors in order to focus the electromagnetic 6
radiation as well as the heat in a thin line. The most optimal design is manufactured and validated on 7
a laminated test sample. The acquired thermographic data are then compared to the data captured 8
in the old-fashioned way with widely available excitation sources. The redesign is also tested on 9
durability and practical use to make sure that it is easy to handle and that it can be used as a long-term 10
solution. Experienced inspectors evaluated the ease of use of it in comparison to the existing sources. 11
A redesigned excitation source minimises the generated biasing side-effects resulting in more energy 12
efficient and safer measurements.

This paper presents the experimental results obtained with a post-peak loading device of hydraulic fracture controlled by setting circumferential deformation of a specimen to be a closed-loop feedback signal during servo-water-driven and monitored with the optical technique of speckle-shearing interferometry (SSI). The macro-scale complete loading curve obtained by the post-peak loading system indicate the stiffness, peak strength and post-peak behavior of quasi-brittle material subjected to borehole water pressure. The micro-scale out-of-plane displacement (OPD) obtained by SSI corresponding to complete loading curve was exhibited where the internal crack tip was located. The complete hydrofracture evolution from displacement continuity to displacement discontinuity was investigated. The test results provide a better understanding of the hydraulic fracture mechanism which is helpful for the development of theoretical and numerical solutions related to hydraulic fractures.

The ever-increasing use of composite materials in the industry has resulted in the need for new, intricate approaches to not only properly characterize their anisotropic mechanical properties (i.e. the visco-elastic tensor), but also to detect various types of internal flaws. Both goals can be achieved by the Ultrasonic Polar Scan (UPS). During an UPS experiment, a material spot is insonified at many oblique incidence angles Ψ(θ,φ), with θ the vertical incident angle and φ the in-plane polar angle, after which the reflected or transmitted ultrasound signal is recorded. The resulting dataset provides an integral view of the angle-dependent reflection (R) and transmission (T) scatter coefficients, and can be employed to infer the material properties. Although the current UPS scanner provides highly accurate experimental data, it is impractical for in-situ measurements. In order to create a more compact and practical measuring device, we propose the use of a hemispherical phased array, consisting of small piezoelectric elements, to generate a broadband, quasi plane wave signal. It will be shown, based on simulations, that a circular phased array concept allows for the determination of the reflection coefficients in space, from which the dispersion curves can be immediately inferred. Comparison of these results with the plane wave theoretical results show an excellent agreement.

Digital Image Correlation (DIC) is used to track the deformation of a cantilever beam at a measurement-point located away from the loading-point. A baseline test is run using the assumption of a linear relationship between the measurement point and the loading point. A second test is run that introduces a PID control based on the DIC measurements. This second method showed an improved ability to follow a cyclic command signal, with the X displacement improving from 14.1% to 6.1% error, the Y displacement from 3.8% to 1.25%, and the Z rotation from 3.2% to 2.0%.