Abrupt Failure Research Articles

Analysis of selected shear strength models based on research of beams without stirrups

The paper presents two theoretical models for calculating shear capacity of beams without stirrups. The analysis refers to slender concrete beams without transverse reinforcement flexurally reinforced with two types of bars: steel and composite (glass fiber reinforced polymer - GFRP). The research program included 29 single-span, simply supported T-section beams without transversal reinforcement. The three point loaded beams (with span to depth ratio a/d in the range of 2.9-3.0 referring to the slender beams). The four times lower modulus of elasticity of the GFRP reinforcement revealed a gentle, progressive shear - tension failure mode, opposite to the abrupt failure mode of the RC beams.

Flatwise Compression and Local Indentation Response of 3D-Printed Strut-Reinforced Kagome with Polyurethane Filling

Additively manufactured lattice structures are finding wider applications as core materials because of their high specific strength, modulus, and energy absorption. Strut-reinforced Kagome (SRK) structures have been shown to have good compressive performance compared with many existing lattice structures. Herein, the performance of acrylonitrile butadiene styrene (ABS) SRK lattice structures fabricated by fused deposition modeling under flatwise compression and local loading was investigated with and without polyurethane foam fillers. The SRK structure demonstrated abrupt failure at the joints in the vicinity of the face sheet, thereby reducing the energy absorption of the structure. The SRK filled with low-density polyurethane foam had no significant effect on peak failure load and moduli, whereas energy absorption per unit mass was higher by 16.5%. The SRK filled with high-density foam showed 116% increase in energy absorption. Similarly, a stronger indentation response was observed with high-density foam-filled SRK sandwich structures.

Bending performance evaluation of aluminium alloy tubes filled with different cellular metal cores

A comprehensive bending performance and energy absorption capability of aluminium alloy tubes filled with different cost-effective cellular metal cores were experimentally evaluated for the first time. The following cellular metal cores were evaluated: i) Advanced Pore Morphology (APM) foam, ii) hybrid APM foam and iii) Metallic Hollow Sphere Structures (MHSS). The results have been compared also with the performance of aluminium alloy tubes filled with (ex-situ and in-situ) closed-cell aluminium alloy foam. The three-point bending tests have been performed at two loading rates (quasi-static and dynamic) and supported by infrared thermography to evaluate the deformation mechanism, damage progress and failure modes. A thorough heat treatment sensitivity (due to the fabrication procedures of composite structures) study on the aluminium tubes has been performed as well. The results show that a reliable and predictable mechanical behaviour and failure can be achieved with proper combination of tubes and cellular metal core. A low scatter of bending properties and energy absorption capability has been observed. The hybrid APM and the ex-situ foam filled tubes achieved the highest peak load. However, they also exhibit a rapid load drop and abrupt failure once the structure has reached the peak load. The APM, MHSS and in-situ foam filled tubes show more ductile behaviour with a predictable failure mode.

Investigation on the pore characteristics of coal specimens with bursting proneness

To achieve further insight into the pore characteristics, the coal specimens with different bursting proneness before and after uniaxial compression failure are tested and compared in this paper. The data of mercury intrusion test is corrected by that of low-temperature nitrogen adsorption and desorption test (LTNAD). The pore size distribution and pore volume of specimens are obtained. The pore compressibility coefficient is determined based on the fractal dimension of pore. Scanning electron microscope (SEM) and computed tomography (CT) are combined to evaluated the pore connectivity. The value of pore compressibility coefficient of specimens with high bursting proneness is larger than that of medium bursting proneness. It means more compressibility and abrupt failure under stress. The researches of both SEM and CT indicate that the pore connectivity of specimens with medium bursting proneness is better. The results show that great differences exist in the pore characteristics of specimens with high and medium bursting proneness, and uniaxial compression failure exacerbates the complexity of pore characteristics.

Temperature effects on the bond behavior between deformed steel reinforcing bars and hybrid fiber-reinforced strain-hardening cementitious composite

The authors have recently developed a hybrid fiber-reinforced strain-hardening cementitious composite (HFR-SHCC) using steel and polyvinyl alcohol (PVA) fibers. When subjected to high temperatures (up to 800 °C), this HFR-SHCC retains a higher proportion of its tensile strength compared to SHCCs containing only PVA fibers. The objective of the current study is to experimentally investigate whether the improved material properties of HFR-SHCC at high temperatures lead to better bond with conventional deformed steel reinforcing bars (rebar) compared to other SHCCs and conventional concretes. Rebar pullout specimens with a deformed rebar centrally embedded inside a SHCC/concrete cylinder were used in this study to determine the rebar-matrix bond. The bond behavior of HFR-SHCC with deformed steel rebar was compared with two concretes of different compressive strengths, a commonly used PVA-SHCC containing only PVA fibers, and a PVA-SHCC with very high content of fly ash. The rebar pullout specimens were subjected to temperatures of 100 °C, 200 °C, 400 °C, 600 °C and 800 °C and were tested after cooling down to room temperature to determine the residual bond strength. Results show that while the specimens made with the conventional concretes exhibit the largest bond strength at room temperature, the specimens made with HFR-SHCC retain the largest proportion of their room temperature bond strengths after exposure to high temperatures and show a more ductile pullout behavior instead of the abrupt splitting failure exhibited by the other materials.

Mechanical and energy absorption characteristics of additively manufactured functionally graded sheet lattice structures with minimal surfaces

Functionally graded (FG) lattice structures have attracted attention for their potential application in lightweighting and energy absorption. In this study, functionally graded sheet (FGS) structures with primitive (P) and gyroid (G) minimal surfaces were fabricated by selective laser melting (SLM) using Ti-6Al-4V powder. The mechanical properties, deformation behavior, and energy absorption performance of uniform sheet (US) and FGS lattice structures were systematically investigated using compression tests and the finite element method (FEM). The FGS structures were found to eliminate abrupt shear failure and to exhibit the predictable layer-by-layer deformation accompanied by sub-layer collapse. The cumulative energy absorption per unit volume of FGS samples increased as a power of strain function throughout the compression process, while the US samples exhibited a linear relationship, thus resulting in an excellent energy absorption capability for FGS structures. The energy absorption of FGS samples was higher than for US samples by approximately 60%. In addition, the results of FEM with the Johnson-Cook models demonstrated a high capability for predicting the deformation behaviors as well as mechanical properties (especially in terms of yield strength, compressive strength and energy absorption) of lattice structures. which can be used to provide guidance on selecting a lattice structure to meet multifunctional demands.

Accumulative Display Updating for Intermittent Systems

Electrophoretic displays are ideal for self-powered systems, but currently require an uninterrupted power supply to carry out the full display update cycle. Although sensible for battery-powered devices, when directly applied to intermittently-powered systems, guaranteeing display update atomicity usually results in repeated execution until completion or can incur high hardware/software overheads, heavy programmer intervention and large energy buffering requirements to provide sufficient display update energy. This paper introduces the concept, design and implementation of accumulative display updating, which relaxes the atomicity constraints of display updating, such that the display update process can be accumulatively completed across power cycles, without the need for sufficient energy for the entire display update. To allow for process logical continuity, we track the update progress during execution and facilitate a safe display shutdown procedure to overcome physical and operability issues related to abrupt power failure. Additionally, a context-aware updating policy is proposed to handle data freshness issues, where the delay in addressing new update requests can cause the display contents to be in conflict with new data available. Experimental results on a Texas Instruments device with an integrated electrophoretic display show that, compared to atomic display updating, our design can significantly increase accurate forward progress, decrease the average response time of display updating and reduce time and energy wastage when displaying fresh data.

A forensic analysis of the Florida International University pedestrian bridge collapse using incident video footages

On March 15, 2018, a Florida International University (FIU) pedestrian bridge near Miami, Florida collapsed during construction. The abrupt failure resulted in casualties and garnered worldwide attention. In the present study, a preliminary forensic analysis of this incident was carried out using limited evidence collected from the collapse scene videos recorded by bystanders. This study is limited in its scope in that it is confined to the examination of how the sequence of failures unfolded by interpreting the rough measurements extracted from the videos through the prism of a physics-based (finite element) model of the bridge. The study does not attempt to explore why this incident may have happened. Nevertheless, by identifying how the collapse occurred, it may be possible to better understand the root causes of this unfortunate incident by combining this information with other, more detailed forensic data. Incidentally, this study provides a new avenue for structure collapse analysis by exploiting incident scene videos and wreckage photos obtained from the public domain.

P973Intravascular lithotripsy for lesion preparation in calcified coronary lesions: a prospective, observational, two-center registry

Abstract Background Intravascular coronary lithotripsy (IVL) is a novel alternative treatment for heavily calcified lesions. This study sought to determine the strategy success and safety of IVL on calcified lesions in an all-comers cohort of patients. Methods Patients with moderate and severely calcified coronary lesions were screened in two centers in Spain and Germany starting April 2018. Until February 2019, 61 patients with 67 lesions were eligible for IVL. Patients were assigned to the following groups: A) Primary IVL therapy for patients with circumferential calcified de-novo coronary lesions (n=32), B) Secondary IVL therapy for patients with moderate or severe calcified coronary lesions in which conventional non-compliant balloon dilatation failed (n=18) and C) Tertiary IVL therapy in patients with in-stent stenosis due to stent underexpansion after previous stenting (n=17). Primary endpoint was strategy success and safety outcome. Strategy success was defined as successful stent delivery and expansion with attainment of <20% in-stent residual stenosis of the target lesion. Safety outcome were procedural complication, defined as coronary dissection, slow or no-reflow phenomenon, new coronary thrombus formation during PCI, abrupt vessel closure and device failure (inability to place the balloon, malfunction, or burst) and in hospital MACE. Results 61 patients with 67 calcified lesions were treated with IVL. Mean diameter of calcified stenosis on quantitative coronary angiography was 72.02±13.8% at baseline and decreased to 17.7±15.84% (p-value: <0.01) after IVL with an acute gain of 1.9±0.63 mm. Mean minimal lumen diameter was 1.0±0.5 mm at baseline and increased after IVL to 2.9±0.6 mm. The overall average of applied pulses was 63±22. The primary endpoint of strategy success was reached overall in 85.2% of patients. 4 type b dissections (3 in group A, 1 in group B) were observed without further sequelae. There were no in-hospital MACE. In one patient (1.6%) non-ischemia driven target lesion failure was observed in routine follow up coronary angiography and was in need for revascularization. According to the subgroups, strategy success in primary IVL treatment (group A) and secondary IVL treatment (group B) was reached in 81.3% and 83.3% of cases, respectively. In tertiary IVL therapy (group C), the primary study endpoint was reached in 64.7% of cases. Device delivery and IVL treatment of target lesion could be performed in all lesions without vessel complications. 7 IVL balloons ruptured during treatment without any sequelae. Rupture was observed in most cases after repositioning of the balloon within the calcified lesion. Conclusions IVL provides a valid strategy for lesion preparation in severely calcified coronary lesions, with high success rate, and low procedural complication and MACE rates. Longitudinal studies will confirm if these favourable initial results of IVL-supported PCI are followed by good long-term results.

Design and analysis of roto – Cylindrical wing for a drone aircraft

Abstract Drone is an aircraft, which is specially designed without the aid of pilots. Drones are used in many areas such as surveillance, military and agricultural applications. The conventionally used drone aircrafts have been analyzed and some drawbacks have been found out in taking off as it requires long take off distance. This work aims to design an effective magnus wing rotor for a drone aircraft and to implement the same in the surveillance industry and in reconnaissance so as to make sure that the current indifference in applying the magnus wing rotor is eliminated by the effective functioning of the UMV Rotor. This refurbished design will increase the reliability of the magnus wing UMVs and it will equalize the commercial value with the other type of drone vehicles. The lift force generated by the fixed aircraft and the quadcopter is very less when compared to the magnus wing UMVs with the similar wingspan and fuselage geometry. The wingspan is greatly reduced by the magnus wing application and it can carry greater payload with tremendous lift force generation. The main objective of the proposed work is to redesign the rotor with the axially fixed spiral spokes which theoretically increases the vortex strength of the UMVs thereby increasing the lift of the cylinder as per the analytical calculation and the analysis of the particular drone design. The magnus wing rotor has a drawback as it suffers an abrupt lifting failure when there is any power cut off. The span discs attached at the ends will reduce the jeopardy by acting like a flywheel as a temporary energy storage mechanism and thereby giving an option for the application in the relevant industries.

What causes sudden death in patients with chronic heart failure and a reduced ejection fraction?

Sudden death characterizes the mode of demise in 30–50% of patients with chronic heart failure and a reduced ejection fraction. Occasionally, these events have an identifiable pathophysiological trigger, e.g. myocardial infarction, catecholamine surges, or electrolyte imbalances, but in most circumstances, there is no acute precipitating mechanism. Instead, adverse left ventricular remodelling and fibrosis creates an exceptionally fragile and highly vulnerable substrate, which can be characterized using the model developed in theoretical physics of ‘self-organizing criticality’. This framework has been applied to describe the genesis of avalanches, nodes of traffic congestion unrelated to an accident, the abrupt system-wide failure of electrical grids, and the initiation of cancer and neurodegenerative diseases. Self-organizing criticality within the ventricular myocardium relies on complex adaptations to progressive stress and stretch, which evolve inevitably to an abrupt end (termed ‘cascading failure’), even though the rate of deterioration of the underlying disease process has not changed. The result is acute circulatory collapse (i.e. sudden death) in the absence of an identifiable triggering event. Cascading failure in a severely remodelled or fibrotic heart can become manifest electrically as a first-time ventricular tachyarrhythmia that is responsive to the shock delivered by an implantable cardioverter-defibrillator (ICD). Alternatively, it may present as an acute mechanical failure, which is manifest as (i) asystole, bradyarrhythmia, or electromechanical dissociation; or (ii) incessant ventricular fibrillation that persists despite repetitive ICD discharges; in both instances, the sudden deaths cannot be prevented by an ICD. This conceptual framework explains why anti-remodelling and antifibrotic interventions (i.e. neurohormonal antagonists and cardiac resynchronization) reduce the risk of sudden death in patients with heart failure in the absence of an ICD and provide incremental benefits in those with an ICD. The adoption of anti-remodelling and antifibrotic treatments may explain why the incidence of sudden death in clinical trials of heart failure has declined dramatically over the past 10–15 years, independent of the use of ICDs.

A Damage Model for Concrete under Fatigue Loading

For concrete, fatigue is an essential mechanical behavior. Concrete structures subjected to fatigue loads usually experience a progressive degradation/damage process and even an abrupt failure. However, in the literature, certain essential damage behaviors are not well considered in the study of the mechanism for fatigue behaviors such as the development of irreversible/residual strains. In this work, a damage model with the concept of mode-II microcracks on the crack face and nearby areas contributing to the development of irreversible strains was proposed. By using the micromechanics method, a micro-cell-based damage model under multi-axial loading was introduced to understand the damage behaviors for concrete. By a thermodynamic interpretation of the damage behaviors, a novel fatigue damage variable (irreversible deformation fatigue damage variable) was defined. This variable is able to describe irreversible strains generated by both mode-II microcracks and irreversible frictional sliding. The proposed model considered both elastic and irreversible deformation fatigue damages. It is found that the prediction by the proposed model of cyclic creep, stiffness degradation and post-fatigue stress-strain relationship of concrete agrees well with experimental results.

Cell-autonomous FLT3L shedding via ADAM10 mediates conventional dendritic cell development in mouse spleen

Conventional dendritic cells (cDCs) derive from bone marrow (BM) precursors that undergo cascades of developmental programs to terminally differentiate in peripheral tissues. Pre-cDC1s and pre-cDC2s commit in the BM to each differentiate into CD8α+/CD103+ cDC1s and CD11b+ cDC2s, respectively. Although both cDCs rely on the cytokine FLT3L during development, mechanisms that ensure cDC accessibility to FLT3L have yet to be elucidated. Here, we generated mice that lacked a disintegrin and metalloproteinase (ADAM) 10 in DCs (Itgax-cre × Adam10-fl/fl; ADAM10∆DC) and found that ADAM10 deletion markedly impacted splenic cDC2 development. Pre-cDC2s accumulated in the spleen with transcriptomic alterations that reflected their inability to differentiate and exhibited abrupt failure to survive as terminally differentiated cDC2s. Induced ADAM10 ablation also led to the reduction of terminally differentiated cDC2s, and restoration of Notch signaling, a major pathway downstream of ADAM10, only modestly rescued them. ADAM10∆DC BM failed to generate cDC2s in BM chimeric mice with or without cotransferred ADAM10-sufficient BM, indicating that cDC2 development required cell-autonomous ADAM10. We determined cDC2s to be sources of soluble FLT3L, as supported by decreased serum FLT3L concentration and the retention of membrane-bound FLT3L on cDC2 surfaces in ADAM10∆DC mice, and by demonstrating the release of soluble FLT3L by cDC2 in ex vivo culture supernatants. Through in vitro studies utilizing murine embryonic fibroblasts, we determined FLT3L to be a substrate for ADAM10. These data collectively reveal cDC2s as FLT3L sources and highlight a cell-autonomous mechanism that may enhance FLT3L accessibility for cDC2 development and survival.

Numerical Investigation of Radial Strain-Controlled Uniaxial Compression Test of Äspö Diorite in Grain-Based Model

A complete stress–strain curve is difficult to obtain for Class II rocks because of the abrupt failure after peak stress. Although the servo-controlled loading system has been used successfully in laboratory tests to analyze the failure of Class II rocks, improved simulation techniques are still needed to control the failure of Class II rocks. In this study, the Class II behavior of Aspo diorite was reproduced explicitly using the GBM-UDEC model. The relative differentiations in all mechanical properties between the simulation and laboratory tests were within ± 5%, such as Young’s modulus, and slope of the post-peak stress–strain curve. Based on the stress and crack generation in UCS test simulation, the failure behavior of the Aspo diorite in the post-peak stress region could be classified into three stages: (V) unstable crack growth with decreasing stress, (VI) stable crack growth with increasing stress, (VII) unstable crack growth, and failure of the rock specimen with decreasing stress. Throughout the simulation, the microcrack investigation was conducted in the aspect of number, angle, relative strength of contacts, and location. In the pre-peak stress region, the cracks between 0° and 20° with respect to axial stress was dominant with over 62% of population among total cracks. Cracks were generated preferentially in relatively weak contacts. The ratio of brakeage in the weakest contact was 22%, while the average breakage value of the other stronger contacts was 16%. In the post-peak stress region, the number of cracks generated between 20° and 40° was approximately 1.4 times higher than those between 0° and 20° at Stages V and VII. There was a significant increase in the number of cracks in the strongest contacts when the model was at the beginning of Stage V and Stage VII. In Stage VII, microcracks were generated intensively in central column of the rock model. Moreover, crack coalescence was monitored in the inner column and rock spalling, complete detachment of block in rock specimen model, was observed at the lateral side of the rock model in Stage VII. In the energy calculation, 23% of the strain energy stored in the model was extracted immediately after peak stress to prevent the violent failure of the rock and most of the energy extracted resulted from grain blocks compared to contacts.

Fault diagnosis based on measurement reconstruction of HPT exit pressure for turbofan engine

Aero-engine gas path health monitoring plays a critical role in Engine Health Management (EHM). To achieve unbiased estimation, traditional filtering methods have strict requirements on measurement parameters which sometimes cannot be measured in engineering. The most typical one is the High-Pressure Turbine (HPT) exit pressure, which is vital to distinguishing failure modes between different turbines. For the case of an abrupt failure occurring in a single turbine component, a model-based sensor measurement reconstruction method is proposed in this paper. First, to estimate the missing measurements, the forward algorithm and the backward algorithm are developed based on corresponding component models according to the failure hypotheses. Then, a new fault diagnosis logic is designed and the traditional nonlinear filter is improved by adding the measurement estimation module and the health parameter correction module, which uses the reconstructed measurement to complete the health parameters estimation. Simulation results show that the proposed method can well restore the desired measurement and the estimated measurement can be used in the turbofan engine gas path diagnosis. Compared with the diagnosis under the condition of missing sensors, this method can distinguish between different failure modes, quantify the variations of health parameters, and achieve good performance at multiple operating points in the flight envelope.

Identification and characterization of spatter particles and their effect on surface roughness, density and mechanical response of 17-4 PH stainless steel laser powder-bed fusion parts

As an emerging additive manufacturing (AM) process, laser powder-bed fusion (LPBF) provides a new prospect for production of complex metallic parts. Laser-material interaction and melt pool dynamics govern the physics behind the LPBF process. However, instabilities in melt pool dynamics lead to the formation and ejection of spatter particles, which are known to change the powder-bed characteristics thus affecting the quality of printed parts. In this work, a comparative study is performed on the virgin and spatter powder particles where two types of spatter particles so-called: under-size (US) and over-size (OS) spatters are studied. Chemical composition, crystallographic phases, microstructure and morphology of the virgin powder as well as the US and OS spatters of 17-4 martensitic/precipitation hardened (PH) stainless steel (SS) powders are studied in detail. Particle analysis results show a significant morphology and size difference between the virgin (D90 – 60 μm) powder, US (D90 – 80 μm) and OS (D90 – 130 μm) spatters. Effect of spatter particles on the surface roughness, density and tensile response of printed parts is also studied. Compared to the parts printed in the non-spatter rich (NSR) region, parts printed in the spatter rich (SR) zone show a 15% and 28% increase in surface roughness for tensile and cylindrical samples, respectively. In addition, higher porosity is observed in these parts with larger pores. Moreover, tensile response shows an abrupt failure resulting in a reduction in ductility due to the presence of large pores (∼100 μm) observed on the fracture surface and x-ray computed tomography results.

A numerical-experimental evaluation of the fatigue strain limits of CFRP subjected to dynamic compression loads

The use of composite materials in the most varied industrial sectors has increased considerably in recent years, especially those made of carbon fiber/epoxy resin. For this reason, the use of these materials need a better understanding of their mechanical behavior, especially when submitted to cyclical load requests, especially about compression, which is the object of study of this work. Residual strength degradation in CFRP is evaluated by numerical models and experimental tests relating the residual strength to the applied fatigue cycles and the maximum stress. The present work proposes to characterize the static and fatigue mechanical properties in compression of a carbon fiber/epoxy resin composite, used in the aeronautical industry, to present a mathematical model to determine the residual strength. The experimental methodology for strain limit evaluation has involved the residual strength after the fatigue test limited to 120,000 or 240,000 cycles, considering frequency of 12 Hz and stress ratio R=10 in different strain levels. This study establishes that the strain limit corresponds to deformation in which the residual strength becomes equal to the design stress (stress reduced statically to the B − basis value). Lastly, the adjusted mathematical model for determining the residual strength and the finite element simulations showed consistent results when compared with experimental tests. This study shows the relevance of the allowable levels determined from static strength to the onset of abrupt failure as a function of increasing maximum fatigue stress level that is a significant finding for the fatigue design community.

Long term veno-venous extracorporeal life support without intravenous anticoagulation for diffuse alveolar hemorrhage

Diffuse alveolar damage is the histologic hallmark for the acute phase of acute respiratory distress syndrome and can occasionally present as diffuse alveolar hemorrhage. We report a patient with diffuse alveolar hemorrhage and acute respiratory distress syndrome requiring veno-venous extracorporeal life support for 210 days, who was successfully treated for a period of 130 consecutive days without intravenous anticoagulation. Although there are a few brief reports detailing long extracorporeal life support runs, the literature is largely devoid of data regarding long-term extracorporeal life support without full systemic anticoagulation. Regular inspection of the extracorporeal membrane oxygenation circuit is critical because externally visible thrombi may predict internal thrombus generation with the potential for systemic embolization or abrupt oxygenator failure. In our case, multiple circuit and oxygenators changes were required. We have demonstrated that a patient with a contraindication for systemic anticoagulation can safely have veno-venous extracorporeal life support for prolonged periods without catastrophic thrombotic complications.

Investigations on acoustic emission parameters during damage progression in shear deficient and GFRP strengthened reinforced concrete components

Shear deficiency in reinforced concrete (RC) structures brings the vulnerability of brittle and abrupt failure to those structures, and thus, provides very little time for taking any precautionary actions. The present study focuses on the investigations on damage progression in shear deficient RC components using acoustic wave propagation technique. Three levels of shear deficiency with respect to the control beam are considered. Various acoustic parameters are considered to determine their efficacy in identifying the initiation and propagation of crack in concrete structures. Few of the acoustic parameters are identified to be very effective and able to clearly differentiate the tensile and shear cracking in concrete. Intensity characteristics, as identified in the present study, can be used to classify the type of damage (progression of shear and tensile cracks) under different stages of loading. Further, the acoustic emission monitoring technique is employed for detecting the crack initiation in strengthened beams where the critical shear deficient beam was strengthened using two layers of GFRP fabric in the shear zone. It is found that, unlike the original deficient beams, AE signals obtained from the strengthened beam clearly indicate the clear shift from shear failure to flexural failure. The present study underlines that the acoustic wave propagation technique can be effectively used to monitor the health of the reinforced concrete structures and to uniquely assess the appropriateness of any scheme(s) for strengthening of the deficient concrete structures.

On the 3D extension of failure models for adhesive joints under mixed-mode fracture conditions: LEBIM and CZM

Interface models for triggering damage events have been extensively used in many engineering applications due to their inherent versatility and relatively simple numerical implementations. Usually, the non-linear behavior of interfaces and thin adhesive joints between solids has been modeled using Cohesive Zone Models (CZMs) although other alternative models have been proposed as well. This is the case of the recently proposed Linear Elastic-Brittle Interface Model (LEBIM). The LEBIM is characterized by a linear constitutive law (traction-relative displacement relationship) in the undamaged state up to failure. Damage occurs when a material point reaches a critical energy release rate leading to an abrupt failure representation. Currently, from the numerical point of view, a great deal of research dealing with interface debonds and adhesive failure is still mainly focused on 2D models. The aim of the present investigation is to extend the LEBIM (originally proposed for 2D problems) for its applications to 3D problems under general fracture conditions and to examine its reliability against experimental data and cohesive-based interfaces pinpointing the main theoretical and numerical differences with respect to alternative methods. Thus, we focus our attention on addressing the main advantages of the proposed LEBIM over the nonlinear CZMs: (i) a simple interface law without the need of triggering a gradual stiffness degradation, (ii) a reliable accuracy in comparison with experimental results, endowing a clear identification of the crack front due to the preclusion of the fracture process zone concept, and (iii) a very high efficiency in terms of mesh requirements stemming from the absence of nonlinear cohesive crack representation. To show that 3D LEBIM is feasible it is implemented into the general purpose Finite Element Method (FEM) package ABAQUS through the user subroutine UMAT. Finally, special attention is given to the adequate treatment of the mixed mode fracture that may appear in complex 3D crack propagation cases.