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Highlights Pipelines for water, oil, or gas transportation are prone to cracking damage due to severe service conditions. Carbon fiber reinforced polymer (CFRP) composites have been applied to repair cracked pipelines. In the present paper, fiber Bragg grating (FBG) and Brillouin optical time domain analysis (BOTDA) technology were applied to monitor the circumferential strains of the steel pipes and CFRP confined seamless/cracked steel pipes in hydrostatic testing. The finite element model (FEM), and the mechanical model were used to verify and analyze monitored strains. The results showed that FBG achieved real‐time and high‐precision strain monitoring with an error of less than 9.3%, better than BOTDA (less than 22.0%). Compared with FBG, the strain of FEM showed that the error of seamless pipe is less than 6%, and the error of cracked pipe is less than 15%. FEM strain field analysis revealed the failure mode of the confined cracked pipe in tensile fracture of structural adhesive between CFRP and steel substrate. The debonding was identified by the sudden strain drops (4.3%–26.2%) in the cracked area. The leakage was identified by a sudden drop (53.0%) in the slope significantly and fluctuations from the curve of strain and hydrostatic pressure after failure. Sensor‐embedded CFRP confined cracked pipes prevent leakage and monitor strain. Multiple FBG sensors are more accurate to monitoring the pipe strain than BOTDA. Debonding of CFRP confined cracked pipes is monitored by the sudden strain drop. Leakage of CFRP confined cracked pipes is detected by strain fluctuations. [ABSTRACT FROM AUTHOR]

The adhesively bonded CFRP (Carbon Fiber-reinforced Polymer) on cracked steel substrate is prone to premature debonding failures due to significant stress concentration resulting from crack opening displacement (COD). This paper presents a theoretical methodology for the crack-dependent bond response of externally bonded CFRP on cracked steel substrate. A bi-linear bond-slip relationship of adhesive is adapted to model the non-linear property of the CFRP-to-steel interface as a cohesive zone. Closed-form solutions of crack-dependent interfacial stress and CFRP stress are derived, considering the elastic, softened, and debonding phases of adhesive. The presented formulations are verified through experiments and numerical simulations. Additionally, the crack-dependent stress distribution is measured by PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) distributed optical fiber sensors in the experiments. The results show good agreement between the analytical solution, measured strain, and finite element (FE) results. Within the range of commonly used design parameters, the interfacial elastic stiffness in the adhesive bond-slip relationship has a significant effect on the peak CFRP stress and interface debonding.

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THz reflective time domain spectroscopy (THz-RTDS) has been considered as an effective method to detect hidden objects with potential for supplementing other NDE technologies for foam composite adhesive structure debonding defects. PMI (Polymethacrylimide) is a heat-resistant foam material, with the highest strength and stiffness to weight ratio. It is widely used in various parts of airplanes, especially the wing leading edge and rudder, landing gear doors, wing-body/wingtip fairings and so on. We analyzed the features of adhesive debonding defect based mainly on the variation of the time-domain wave form and compared with the inclusion defect. The quantification of degrees of adhesive debonding can be readily achieved with THz-RTDS images based on the delay of the wave front and the main reflection time-domain waveforms. Typical accuracy of about 100 μm was achieved. [ABSTRACT FROM AUTHOR]

The understanding of ice shedding is of prime importance in the assessment of aeronautical ice protection systems. In this paper, the authors previously studied mechanism is extended to include adhesive debonding. It is based on pressure redistribution in the water film formed at the ice/airfoil interface. The numerical modelling of crack propagation is based on recent work on damage mechanics which provides a general framework. As for adhesive debonding an algebraic model is derived from general mechanical equilibrium relations. Numerical experiments are performed to study an adhesive-debonding/brittle-failure mode detachment, the results of which are discussed. [ABSTRACT FROM AUTHOR]

• Interactive damage of adhesive joint and composite shell in blade is simulated numerically. • Nonlinear finite element analysis revealed local skin buckling on compression side. • Buckling driven debonding and composite damage is modelled with cohesive zone model and continuum damage mechanics. • Skin-spar joint debonding is the initial damage leading to the blade ultimate failure. Wind turbine blades are continuously upscaled in size to meet the increasing demand of low cost renewable energy. The larger and slender blades with reduced mass are susceptible to large-deflection bending and instability during extreme wind gusts. The loading can induce interactive damage modes such as adhesive bond failure and composite skin damage progressively degrading the blade structural performance. The structural deformation and instability as well as progressive damage in composite blade is analyzed by developing finite element (FE) models using ANSYS software. First, a geometric nonlinear FE analysis of the 3D blade is performed to predict its deflection and regions of high stresses. The results demonstrated that high compressive stresses in the blade suction side trigger local skin buckling; thus initiating debonding of weak adhesive interface joint between skin and spar combined with skin damage. Subsequently, the interactive buckling-driven skin-spar debonding and composite skin damage in the identified region are analyzed through a submodel using cohesive zone model (CZM) as well as continuum damage mechanics (CDM) based progressive failure analysis, respectively, through a user-defined material subroutine. The results indicated that buckling-driven debonding of adhesive interface between skin and spar was primary damage mode leading to progressive failure of the blade composite skin. Consequently, the blade ultimate load carrying-ability was governed by coupled adhesive debonding and progressive skin damage phenomena, which is in good agreement with published experimental results. The developed simulation approach is capable to efficiently analyze the interactive buckling-induced interface damage as well as progressive failure of composite blade structure. In this work, modelling of interaction between interface debonding and skin damage, based on the CZM and CDM scheme, is a novel methodology for progressive damage analysis of blade under extreme loading. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular pull-off simulation of bitumen-aggregate interface was performed. • Cohesive debonding percentage rises with bitumen film thickness and temperature. • Less cohesive and more adhesive debonding occur at higher pull-off velocities. • Stronger alkaline minerals are more prone to have cohesive debonding. When an asphalt mixture cracks, adhesive debonding occurs along bitumen-mineral interfaces and cohesive debonding occurs within bitumen films. At microscale, the two debonding processes can happen simultaneously but it is unknown for their percentages. This study aims to determine the percentages for cohesive and adhesive debonding and investigate how the material and external factors can affect these percentages using molecular dynamics (MD) modeling. The pull-off simulations of bitumen-calcite interfaces were performed at different bitumen film thicknesses, pull-off velocities and temperatures. The percentages of cohesive debonding were calculated as the area ratio of the remained bitumen molecules over the total interface. Results show that the percentage of cohesive debonding increases from 29% to 65% with thicker bitumen films, and decreases from 86% to 59% with higher loading velocities. When temperature rises, the percentage of cohesive debonding increases from 61.3% to 88.2%. Quartz presents a weak adhesion to bitumen, and thus a complete (100%) adhesive debonding occurs regardless of bitumen thickness. Microcline shows a very strong adhesion to bitumen due to its high polarity. The modeled cohesive debonding percentage with different variables were verified and found consistent with the laboratory pull-off testing results available from the existing studies. [ABSTRACT FROM AUTHOR]

• Variational phase-field adhesive/brittle fracture model. • Electromechanical resonant ice protection systems. • Numerical experiments to highlight the fracture path leading to ice shedding. • Adhesive modelling at the ice/substrate interface. • Choice of input parameters. Electromechanical resonant de-icing systems provide a low-energy solution against ice accumulation on aircraft. Recent researches show a growing interest towards these systems in the context of more electrical aircraft. Electromechanical de-icing systems consists in electric actuators producing stress within the ice, through micro-vibrations of the surface to be protected, leading to bulk or adhesive failure and, ultimately, ice shedding. The understanding of the mechanisms at play is of prime importance in order to design efficient ice protection systems. Despite a large number of studies in the literature, there is still a lack when dealing with fracture propagation phenomena in this context. In this work the authors propose a model based on the well established phase-field variational approach to fracture. The approach is applied to the study of crack propagation and debonding of ice under the effect of an electromechanical resonant de-icing system. Numerical experiments are performed in order to assess possible ice shedding mechanisms. [ABSTRACT FROM AUTHOR]