Partial Debonding Research Articles

Electromagnetic Stress Analysis of High-Temperature Superconducting Coated Conductor Strip After Partial Debonding at the Edge Under the Combined Transport Current and Magnetic Field

Electromagnetic Stress Analysis of High-Temperature Superconducting Coated Conductor Strip After Partial Debonding at the Edge Under the Combined Transport Current and Magnetic Field

Flexural strengthening of reinforced concrete cantilever beams having insufficient splice length

Structural systems often undergo changes due to variations in the usage, the loading conditions, or the presence of defects in their elements. The problem can be exacerbated when there is insufficient overlap between reinforcing bars in critical moment zones. This article investigates the behavior of reinforced concrete cantilever beams exhibiting insufficient overlap between bars that used as main reinforcing steel bars in the negative moment zone. Various strengthening techniques were employed in order to improve these defected cantilever beams. Eleven beams underwent flexural testing until reaching failure. The experimental parameters encompassed the strengthening scenarios and the bonded length. Three strategies were used: the application of stainless-steel plates (SSPs) as externally bonded reinforcement, near surface mounted (NSM) reinforcement in which additional deformed steel bars were bonded utilizing engineering cementitious composites, and externally pre-stressing technique. The anchorage length was examined at 40, 50, and 60 times the internal bar diameter. It was noted that the most substantial improvement achieved with the NSM method, followed by the externally pre-stressing method. It is worth mentioning that most of the beams failed in a flexural manner, with partial debonding occurring in beams strengthened using external strengthening. Moreover, this article includes the development of a numerical model employing the finite element method to replicate the response observed from the experimentally tested beams. The accuracy of the model was confirmed through the comparison of its outcomes with the experimental data, demonstrating an acceptable level of accuracy with deviations of less than 4.4 %. This successful numerical investigation was also used to conduct a parametric study. From this study it is evident that the effect of debonding on SSPs can be reduced by adding steel anchors at the ends of these plates. Finally, an analytical method was proposed to calculate the ultimate load capacity of strengthened reinforced concrete beams.

Bending strength degradation of a cantilever plate with surface energy due to partial debonding at the clamped boundary

Bending strength degradation of a cantilever plate with surface energy due to partial debonding at the clamped boundary

Effect of fluid scour on stress distribution of film-substrate system

Under strong fluid scour in special service environment, the film-substrate system is prone to weaken its mechanical properties due to the additional shear stress by fluid, resulting in film debonding. The present study establishes a mechanical model incorporating the fluid shear stress for a film-substrate system with partial debonding. The debonding length, scour strength and thermal mismatch are considered in the model, respectively. Fluid induces compressive stress on inflow side and tensile stress on outflow side. Potential debonding behavior of film by the additional shear stress is qualitatively analyzed. Results show that the compressive stress by fluid releases part of the tensile stress of thermal mismatch, may mitigate surface cracking of film. The surface scour effect is amplified by the partial debonding, and is further enhanced with the increase of debonding length. The unevenness of stress distribution at the interface is intensified by the debonding and fluid scouring. The fluid scour poses a potential threat to the film-substrate system.

Debonding of Porous Coating: A Late Failure Mode of Uncemented, Partially Threaded Acetabular Components—Retrieval Analysis

Titanium plasma-sprayed (TPS) porous coatings have been used in total hip arthroplasty for decades. They are considered reliable, and very few failure cases have been described so far. This retrieval study described a series of 20 acetabular components—where total or partial debonding occurred during in vivo use and aimed to explain the underlying failure mechanisms. Implants were examined using optical and electron microscopy (SEM), metallographic sections of retrievals were prepared while pathologic samples of periprosthetic tissues were examined for presence of wear debris. Data from metallographic slides indicated that debonding was initiated at free borders of the coating and tended to progress at the interface between the TPS layer and the shell. In some cases, total debonding occurred leading material wear of both the TPS layer and acetabular shell leading to massive release of metallic debris and accelerated polyethylene wear in third body mechanism. SEM examination demonstrated that splats forming the TPS layer exhibited features suggesting a high temperature gradient between the plasma sprayed layer and the substrate material existed, leading to porosity of splats and suboptimal bonding strength. This study demonstrated that coating application parameters and certain design features (screw holes, fins) may promote long-term failure due to debonding. Surgeons should be aware of this complication as it is most likely underreported, while manufacturers should consider more rigorous pre-clinical testing as suboptimal coating bonding may result in failures during long-term clinical use.

Study on Bonding Behavior between High Toughness Resin Concrete with Steel Wire Mesh and Concrete

This paper investigates the interfacial bonding behavior between high toughness resin concrete with steel wire mesh (HTRCS) and concrete. A total of five sets of fifteen double shear specimens were tested for parameters including concrete strength and material properties of HTRCS composites. The test results showed that the failure mode of DS1 specimens was partial debonding and fracture, and the rest of the specimens were the fracture of HTRCS. The concrete strength and reinforcement ratios of HTRCS composites were positively correlated with interfacial adhesion properties. When the concrete strength was increased from C30 to C40 and C50, the ultimate load increased by 43.4% and 43.2%, respectively. The ultimate load capacity increased by 32.1%, with the reinforcement ratio of HTRCS composites increasing from 1.05% to 1.83%. Moreover, the bonding slip model and the bearing capacity formula for the interface between HTRCS composites and concrete were proposed, and the calculation values were in good agreement with the test values, with an average value of 0.978.

Guided Wave-Based Early-Stage Debonding Detection and Assessment in Stiffened Panel Using Machine Learning With Deep Auto-Encoded Features

Abstract Debonding between stiffener and base plate is a very common type of damage in stiffened panels. Numerous efforts have been made for debonding assessment in the stiffened panel structure using guided wave-based techniques. However, these studies are limited to the detection of through-the-flange-width debonding (i.e., full debonding). This paper attempts to develop a methodology for the detection and assessment of early-stage debonding (i.e., partial debonding) in the stiffened panel using machine learning (ML) algorithms. An experimentally validated finite element (FE) simulation model is used to create an initial guided wave dataset containing several debonding scenarios. This dataset is processed through a data augmentation process, followed by feature extraction involving higher harmonics of guided waves. Thereafter, the extracted feature is compressed using a deep autoencoder model. The compressed feature is used for hyperparameter tuning, training, and testing of several supervised ML algorithms, and their performance in the identification of debonding zone and prediction of its size is analyzed. Finally, the trained ML algorithms are tested with experimental data showing that the ML algorithms closely predict the zones of debonding and their sizes. The proposed methodology is an advancement in debonding assessment, specifically addressing early-stage debonding in stiffened panels.

Experimental and numerical investigation of the bonding conditions of piezoelectric sensors under high compressive strains on structures

In the past two decades, thin lead zirconate titanate (PZT) sensors have been widely used in the electro-mechanical impedance (EMI) technique for sensing applications, particularly for monitoring civil structures. They are typically surface bonded using an industrial adhesive to the monitored structure. The bond between a PZT sensor and structure must be sufficiently strong to transmit the response of the structure to the sensor. In this study, acrylic cubes bonded with PZT patches are subjected to high compressive strains above 2000 με to develop a better understanding of bonding conditions when structures undergo such high strains. Acrylic can undergo such high strains without developing fissures or cracks. Thus, the recorded EMI response only reflects changes in the bonding condition due to the development of strains. The experiments are also numerically supplemented by simulating various debonding conditions. At higher strains, it was observed that the admittance signatures tend to behave similarly to a freely vibrating PZT patch, indicating debonding around the periphery. Even after the complete unloading of the structure, the signatures did not return to their initial state, indicating a permanent partial debonding. The strains developed on a loaded structure are not uniform and can be localized due to structural imperfections, resulting in higher strains in the region where a sensor is bonded. The insights from this study will aid in expanding the scope of the application of PZT sensors for monitoring civil structures through better comprehension of the PZT-structure bond under high compressive strains.

Characterization of Yttria-Stabilized Zirconia (YSZ) following high temperature hydrogen exposures of molybdenum-YSZ composites

Molybdenum matrix ceramic-metal (cermet) composites containing 40–70 vol% yttria stabilized zirconia (YSZ) particles (as a surrogate for ceramic fuel particles) were produced via spark plasma sintering (SPS) and exposed to flowing hydrogen at high temperature (2000–2630 K). Both steady state and thermally cycled (4 cycles with intermediate cooling to room temperature) conditions were examined for a constant total hot testing time of 80 min. Due to the high hydrogen permeability in Mo at these temperatures, pronounced microstructural degradation was observed in YSZ particles located many millimeters below the sample surface. Observed changes to the YSZ particles from the hot hydrogen testing include partial matrix debonding, thermal expansion, redeposition of material, phase changes to a monoclinic phase and cracking/bubble formation on the YSZ grain boundaries. Overall, the YSZ particles exhibited acceptable tolerance to this extreme operating environment.

Flat-face epoxy-bonded concrete joints loaded in torsion: Physical modelling

Joints in concrete structures must perform under various complex loads including torsion. This paper reports the results of an experimental programme investigating the static torsional performance of epoxy-bonded concrete joints. Torsion tests were performed using a custom experimental setup able to apply torque on a hollow concrete prism with an epoxy joint in the middle. The tested specimens failed in both cohesive and mixed modes. The cohesive failure mode was characterised by cracking in the body of concrete, while the mixed mode also included partial debonding of the joint. The cohesive mode was dominant, more ductile and exhibited higher torsional strength. The cracking behaviour of the jointed specimens was typical of concrete prisms under torsion except that in the mixed mode a crack developed along the joint on two or three specimen sides. Digital Image Correlation, applied for monitoring surface strain, showed that inclined bands of high shear strain passed across the joint during the tests. The mechanism of concrete-epoxy debonding was investigated using two standard testing methods. The low shear strength of concrete near the epoxy joint was identified as the source for the weaker, stiffer and more brittle response of the mixed failure mode in the torsion tests.

Characterization of multi-step cyclic-fatigue hysteresis behavior of 2D SiC/SiC composite using inverse tangent modulus

Under multi-step cyclic fatigue loading, the mechanical hysteresis loops of ceramic-matrix composites (CMCs) were affected by coupled multiple damage mechanisms. In this paper, the hysteresis-based inverse tangent modulus (ITMs) was developed to characterize the cyclic fatigue mechanical hysteresis behavior in 2D SiC/SiC composite under multi-step loading. The micromechanical multi-step hysteresis constitutive models were developed for the damage state of interface partial and complete debonding. Relationships between the cyclic-dependent interface wear, hysteresis loops, interface slip damage state, and ITMs were established. Effects of multi-step peak stress level, cycle number, and interface properties on the evolution of hysteresis stress-strain curves and ITMs were analyzed. Experimental multi-step cyclic fatigue hysteresis loops and ITMs of 2D SiC/SiC composite under different peak stresses of 1.2, 1.3, 1.4, and 1.5 PLS (proportional limit stress) were predicted. Compared with other hysteresis-based damage parameters, e.g., hysteresis width, hysteresis modulus, peak and residual strain, and loops area, the damage parameter of ITMs can better reveal the interface debonding and slip damage state in CMCs under multi-step cyclic fatigue loading.

Experimental research on the flexural behavior of GFRP bar-reinforced composite beams with different shapes of prefabricated UHPC formwork

In this paper, the flexural behavior of eight composite beam with prefabricated permanent ultrahigh-performance concrete (UHPC) formwork and reinforced with glass fiber reinforced polymer (GFRP) bars were investigated based on four-point bending test and calculation. The types of prefabricated permanent UHPC formwork, bottom formwork thickness, and interface treatment methods were studied as experimental variables. It was found that the cracking load of beams with prefabricated permanent UHPC formwork increased by 77.4%–130.8 % compared with that of the reference beam. However, the ultimate bearing capacities of these composite beams, except for those of the beam with two-sided UHPC formwork and that with bottom UHPC formwork with a thickness of 50 mm (no debonding and an increase of 19.0 %), decreased by a maximum of 36.7 % due to the partial debonding between the prefabricated permanent UHPC formwork and core concrete. The overall performance of the composite beam improved as the bottom formwork thickness increased and the interface treatment existed. Based on the test results, a simplified calculation method was developed to predict the cracking moment of composite beams with UHPC formwork. The cracking moment obtained by the proposed calculation method matches the experimental results.

Retrofitting Reinforced Concrete One–Way Damaged Slabs Exposed to High Temperature

Exposure of reinforced concrete buildings to an accidental fire may result in cracking and loss in the bearing capacity of their major components, columns, beams, and slabs. It is a challenge for structural engineers to develop efficient retrofitting techniques that enable RC slabs to restore their structural integrity, after being exposed to intense fires for a long period of time. Experimentalinvestigation was carried out on twenty one slab specimens made of self compacting concrete, eighteen of them are retrofitted with CFRP sheets after burning and loading till failure while three of them (which represent control specimens) are retrofitted with CFRP sheet after loading till failure without burning. All slabs had been tested in a simply supported span and subjected to two-point loading. The main variables were the effect of different temperature levels (300ºC, 500ºC and 700ºC),different concrete compressive strength (20MPa, 30MPa and 40MPa) and cooling rate (gradually and sudden cooling conditions) on the behavior of retrofitted one way slabs .The structural response of each slab specimen was investigated in terms of load-deflection behavior, ultimate load carryingcapacity and mode of failure. The experimental results, generally, indicate that slabs retrofitted using CFRP sheets restored flexural strength values nearly equal to or lower than those of the reference slabs, the retrofitted slabs exhibited larger deflection than the control slabs at ultimate loads. Retrofitted control slabs after loading regained about 93.95% to 97.92% of their original load capacity(before retrofitting) while the other slabs regained from 42.% to 84% of the load capacity of the original control specimens. Most of the tested slabs failed by concrete crushing at mid span and partial debonding of certain retrofitting systems was also observed for a few cases

Effects of nonlinear hyper‐viscoelasticity and matrix/fiber debonding on the mechanical properties of short carbon fiber/styrene‐butadiene rubber composites under cyclic uniaxial loading using a multiscale finite element model

AbstractA multiscale finite element analysis was performed for short carbon fiber (SCF) reinforced rubber composites under uniaxial tensile loading with periodic geometries and random distributions of the short fibers. Three different zones were considered, including the rubber matrix, SCF as the inclusion phase, and a thin matrix layer as the interphase. A nonlinear hyper‐viscoelastic model was selected for the matrix, while linear viscoelastic and elastic models were considered for the interphase and reinforcing phases, respectively. The analyses were carried out on an incremental basis from a lower loading‐unloading rate of 10 mm/min to a higher rate of 100 mm/min. Two interface conditions were considered between the polymer matrix and the SCF phases: perfect bonding and partial debonding. The partial debonding was modeled via extended FEM (XFEM) with a crack initiation criterion. An integral averaging technique was employed to predict stress and strain at the macro‐scale. Based on the observations in this work, hysteresis and energy dissipation decrease with the addition of the short fibers to the neat rubber and surface modification of the fibers under three‐cycle loading. For example, in the first cycle and for a constant stress of 0.45 MPa, the strain value decreases from 0.25 to 0.17 MPa at the loading‐unloading rate of 10 mm/min. The high‐fidelity model developed in this work for short fiber/rubber composites is able to predict the stress and strain responses of the SCF/SBR composites, confirming the accuracy of the utilized multiscale approach.

Development and Characterization of SiC–Mo High-Temperature Multi-layer Laser Flash Artifacts with Partial Debonding

Development and Characterization of SiC–Mo High-Temperature Multi-layer Laser Flash Artifacts with Partial Debonding

Experimental background behind new AASHTO LRFD specifications for partially partially debonded strands

To develop a unified approach for the design of partially debonded strands in prestressed concrete highway bridge girders, a coordinated analytical and experimental investigation was conducted. This investigation examined amounts of partial debonding, distribution of partially debonded strands within the cross section, debonded lengths, locations and staggering of termination of debonded strands, confinement of debonded regions and their termination points, and the impact of adding nonprestressed reinforcement in the region of partial debonding. The results from testing full-scale I- and U-shaped girders indicate that partially debonding strands does not result in deleterious performance if adequate reinforcement is provided to resist the longitudinal tension due to bending and shear. Crack patterns and angles were not noticeably affected by the amount of debonding. Regardless of the debonding ratio, the maximum measured crack widths at the capacities predicted by the eighth edition of the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications remained small. The requirements for debonded strands were revised significantly in the ninth edition of the AASTHO LRFD specifications based on the presented research.

Experimental and numerical study on the influence of cure process on the bridging traction mechanism of z-pins

This paper focuses on the bridging mechanism of individual z-pins embedded in carbon/epoxy laminates with curing effects into account. Based upon experiments, partial debonding exists in the vicinity of z-pins before pullout loading. Despite scatter, bi-linear relationship from load–displacement data is collected to characterize the bridging responses of z-pins. Complete pull-out is the dominant failure mode of z-pins after loading, due to inferior interfacial adhesion. A representative volume element (RVE) model of a single z-pin reinforced composite laminates is established, with resin-rich pockets and interfacial behavior into consideration. A qualitative analysis is presented to evaluate the influence of curing defects on the bridging ability of z-pins. The variations of cure-dependent properties are explicitly modeled. Cohesive elements are applied to the z-pin and interface regions in terms of bi-linear constitutive law. The predictions show reasonably well agreement with the experiments. Remarkably, the mismatched curing residual stresses are responsible for the generation of interfacial cracking around z-pins. The pre-existing cracking provides a reduction of physical interfacial contact, thus adversely controlling the effectiveness of z-pin reinforcement. Furthermore, the influence of cure process on the bridging behavior of z-pins is explored using a parametric method.

Failure mode of cement sheath in salt cavern gas storge wellbore based on coupling plasticity and damage evolution

In this paper, the failure mechanism of the cement sheath in gas storage salt caverns under the cyclic internal pressure and cavity shrinkage was explored. First, an elastoplastic damage evolution model for the completion cement was established and further developed as a constitutive equation for numerical calculation. Second, the verification of the model is completed by mechanical tests and numerical examples, respectively. The uniaxial and triaxial compression tests, Brazilian splitting tests, and cyclic loading tests were performed to verify the theoretical stress-strain curves. Numerical examples were performed to verify the stability of the constitutive equation in numerical simulations. Finally, the constitutive equation is applied to the engineering, and the numerical model calculation of wellbore fatigue damage and salt cavity shrinkage was performed. The following conclusions are obtained: cyclic loading will increase the plastic strain of the cement sheath, and micro-annuluses will form on the inner surface after 25 years of operation. The shrinkage of the salt cavity will debond the outer side of the cement sheath near the open well. With the increase of cavity shrinkage, the range of wellbore failure increases upwards. When the cavity shrinkage rate exceeds 10%, partial debonding will occur on the cemented surface between the cement sheath and the rock salt formation, which may provide a channel for natural gas leakage.

Designing Stress-Adaptive Dense Suspensions Using Dynamic Covalent Chemistry

The non-Newtonian behaviors of dense suspensions are central to their use in technological and industrial applications and arise from a network of particle–particle contacts that dynamically adapt to imposed shear. Reported herein are studies aimed at exploring how dynamic covalent chemistry between particles and the polymeric solvent can be used to tailor such stress-adaptive contact networks, leading to their unusual rheological behaviors. Specifically, a room temperature dynamic thia-Michael bond is employed to rationally tune the equilibrium constant (Keq) of the polymeric solvent to the particle interface. It is demonstrated that low Keq leads to shear thinning, while high Keq produces antithixotropy, a rare phenomenon where the viscosity increases with shearing time. It is proposed that an increase in Keq increases the polymer graft density at the particle surface and that antithixotropy primarily arises from partial debonding of the polymeric graft/solvent from the particle surface and the formation of polymer bridges between particles. Thus, the implementation of dynamic covalent chemistry provides a new molecular handle with which to tailor the macroscopic rheology of suspensions by introducing programmable time dependence. These studies open the door to energy-absorbing materials that not only sense mechanical inputs and adjust their dissipation as a function of time or shear rate but also can switch between these two modalities on demand.

Investigation of surface integrity transition of SiCp/Al composites based on specific cutting energy during ultrasonic elliptical vibration assisted cutting

Different from brittle materials or homogeneous metal materials, there is no obvious characteristic of brittle removal or plastic removal in machining of particle reinforced metal matrix composites (MMCs). In the present work, we investigate the surface integrity transition of SiCp/Al composites during ultrasonic elliptical vibration-assisted cutting (UEVC). The machined surface is divided into two parts: plastic deformation of metal matrix and defects caused by particle deformation. A specific-cutting-energy-based criterion based on the relationship between plastic deformation and defects formation, is established to characterize the surface integrity transition of SiCp/Al composites quantitatively. The effectiveness of the critical cutting parameter is verified by systematic experiments. Experimental results show that the surface integrity transition of SiCp/Al composites is mainly affected by processing method and cutting speed. When the scratching speed increases from 100 mm/min to 200 mm/min, the main part of machined surface changes from defects to plastic deformation accordingly in UEVC. The ductile surface of SiCp/Al composites can be obtained when the cutting speed, cutting depth and feed rate are 100 mm/min, 0.01 mm and 0.02 mm/rev, respectively. According to the experimental results, particle partial fracture, debonding and micro-deflection dominate particle removal process in UEVC, which is also the main reason why UEVC can improve the machinability of SiCp/Al composites.