Deflection History Research Articles

An updated model including the deflection history of microcantilever for characterizing cellular viscoelastic properties by AFM indentation-relaxation test

An updated model including the deflection history of microcantilever for characterizing cellular viscoelastic properties by AFM indentation-relaxation test

Modelling of flexural fatigue behaviours of hybrid engineered cementitious composite link slabs using cycle-driven analysis

Link slabs are designed and expected to be serviced under high-cycle traffic loadings. Although their high-cycle fatigue performance is critical in their practical applications, very few experimental and numerical studies have been conducted to study high-cycle fatigue failure of link slabs due to the huge amount of time and resources needed for fatigue tests and the lack of efficient modelling method for high-cycle fatigue failure. Recently, as a newly developed material with superior mechanical properties, the hybrid fibre reinforced engineered cementitious composite (hybrid ECC) has been recommended for link slab application. In this study, a novel and efficient cycle-driven analysis (CDA) procedure was developed to model the structural behaviour of ECC link slabs made of the hybrid ECC under high-cycle fatigue loadings, which is the first attempt for CDA to be applied in high-cycle fatigue structural modelling of a hybrid ECC link slab with reinforcement bars. In the proposed CDA, fatigue damages of both hybrid ECC and reinforcement bars were taken into account. The accuracy and reliability of the new CDA procedure were validated by comparing the modelling predictions with the experimental results on two quarter-scaled hybrid ECC link slabs. It was found that the proposed CDA procedure could predict the overall fatigue behaviours including the deflection histories, crack patterns, fatigue life, fatigue failure mode and the residual static strength of the hybrid ECC link slabs after fatigue damage with good accuracy.

Medial Pterygoid Abscess Masquerading as a Temporomandibular Joint Disorder: A Case Report.

A patient presenting with a history of restricted mouth opening and deflection of the mandible after a prolonged dental procedure raises a suspicion of temporomandibular joint disorder (TMD) due to its estimated high prevalence of 29%. Muscle relaxants and routine active physiotherapy established normal range of movement and pain reduction was achieved through TENS therapy and analgesics. However, the non-subsidence of deflection prompted an initial suspicion of TMD which was overturned by MRI. The MRI evaluation revealed left side medial pterygoid abscess. It is imperative to understand that despite strong history and relevant clinical features, for the definitive diagnosis radiographic evaluation is highly contributory. Misdiagnosing TMD due to its similar presentation can have significant implications for the patient's well-being and quality of life. The clinical features of medial pterygoid abscess including restricted mouth opening and pain can be similar to that of TMD. These abscesses are most commonly caused by odontogenic infections but can also occur as a result of septic inferior alveolar nerve block techniques. Limited literature reports of pterygoid space abscess have been described, but intramuscular and medial pterygoid abscess is an absolute rarity. Causal relationship to septic inferior alveolar nerve block further makes this case report an interesting read.

Experimental and theoretical study on the response of the X-frame CFRP sandwich beam under the local impulsive loading

The impact resistance of the carbon fibre reinforced X-frame sandwich beam and its foam reinforced structure was investigated experimentally and theoretically. To simulate the blast loading on the composite sandwich beams, the aluminum foam projectiles were utilised to impact the composite specimens. Under the local impulsive loads of the different intensities, the core shear failure, core crushing and skin fracture of the sandwich beams were observed by using a high-speed camera. A theoretical model for the dynamic response of the fibre-reinforced composite sandwich beam under the impact loads was constructed. Three phases, namely the local compression, the propagation of global bending/shearing wave and global stretching were considered in this theory. The theoretical model can provide the reasonable deflection history and failure modes of the sandwich beam compared with the experimental and simulated results. The impact pressure between the foam projectile and the beam were obtained by the theoretical and numerical predictions. The results indicated that the decreasing of the structural density can reduce the transmitted impulse. The optimal design charts were constructed by introducing the normalised variables based on the theoretical model. The minimum weight design revealed that the composite sandwich beams with low-density cores generally had the better specific impact resistance, while the foam-filled sandwich beams with the higher density had the outperformed impact resistance at the low impulse. It is expected that the theoretical model can provide a useful reference for predicting the impact resistance of the fibre-reinforced composite sandwich structures.

Round-ended concrete-filled steel tube columns under impact loading: Test, numerical analysis and design method

This paper reports experimental and numerical investigations on the behaviours of round-ended concrete filled steel tube (RE-CFST) columns under combined pre-axial and impact loadings. Twelve RE-CFST specimens were tested to assess the influences of the cross-sectional aspect ratio, impact velocity and pre-axial loading on the impact-resisting performance. The failure patterns, impact force and mid-span deflection histories were obtained and analyzed. Test results showed that increasing pre-axial loading led to a decrease in the plateau impact force and an increase in the mid-span deflection. In addition, the finite element (FE) models were developed and calibrated with the experimental data, and then employed for evaluating the working mechanism of typical RE-CFSTs during the whole impact process and performing parametric investigations. According to the experimental and numerical results, empirical formulae were proposed for predicting the plateau impact force of RE-CFST columns subjected to lateral impact.

Dynamic response of fully clamped sandwich pipes under transverse localized impulse

The development of sandwich pipes is propelled by the demands of both submarine pipelines and lightweight energy absorbers. Because of the complexity of impulse related to the traveling of plastic hinges, the plastic behaviors of sandwich pipes under transverse localized impulse are still not well understood despite the structures are susceptible to underwater explosions caused by explosives and torpedoes. In the present paper, a theoretical model is proposed by dividing the entire response into three successive phases according to the traveling of the plastic hinges. Based on the yield loci for the cross-section of a sandwich pipe proposed in our previous work, the deflection histories and the maximum deflection of the sandwich pipe are predicted theoretically and compared with the numerical results. Well agreements are achieved between the theoretical predictions and the numerical results. It is demonstrated that the loading areas have remarkable effects on the dynamic response of the structure. The present work provides a basic understanding of the plastic behaviors of sandwich pipes threatened by transverse impulse.

Low-velocity impact behavior of elliptic curved composite structures

Although many composite structures are inconsistently curved, such as the leading edges of aircraft wings, the variety of research in impact engineering is almost limited to the impact performance of plates or cylindrically curved specimens. It is not known whether the findings obtained from standardized tests can be transferred to curved structures or which adaptions are required. Therefore, a deeper understanding of the deformation and damage behavior of inconsistently curved structures is essential to transfer the observed impact behavior of flat specimens to general curved structures and therefore to utilize the full lightweight potential of a load-specific design. An accurate description of the procedure as well as the results of the experimental and numerical study of the low-velocity impact behavior of differently single-curved elliptic specimens is presented. To close the research gap of the impact behavior of geometries with curvatures between the plates and simplified leading edges, novel specimens geometries have been derived from established impact test standards. Glassfiber-reinforced specimens are subjected to an instrumented impact test at constant impact energy. This is numerically investigated by a stacked-layer model, which used cohesive zone modeling to enable the simulation of matrix cracking, fiber fracture and delamination. The resulting projected damage areas, as well as the force and deflection histories, were evaluated and section cuts were examined to discuss the damage morphology, formation and propagation process. Significant effects on maximum deflection, compliance and dynamic behavior on the size and morphology of damage were found.

Impact resistance of flax FRP fully wrapped coconut fibre reinforced concrete beams and shear contribution of FRP

This study investigates the behaviour of flax fibre reinforced polymer (FFRP) fully wrapped coconut fibre reinforced concrete (CFRC) beams and FRP contribution to shear strength under impact loadings. Both repeated and single drop-weight tests were carried out on the beams, with a dimension of 500 mm × 100 mm × 100 mm and three different FFRP wrapping thicknesses. For the repeated impact tests, the impact reaction force, deflection histories and FRP strains were recorded and analysed to investigate the influence of FFRP wrapping thickness on the impact resistance. For the single impact tests, the energy absorption, failure modes and the shear contribution of FFRP in CFRC beams was studied. The results showed that the impact resistance of the fully FFRP wrapped beams showed a non-linear increase tendency with thickness. The damage mechanism of concrete beams is also influenced by the FRP thicknesses. The analytical results of shear contribution of FFRP were calculated by considering the dynamic increase factor, which fits well with experimental values, indicating that the proposed method is reasonable.

Dynamic analysis of single–layered graphene sheet subjected to a moving nanoparticle: A molecular dynamics study

The dynamic response of a single–layered graphene sheet (SLGS) subjected to a moving nanoparticle is investigated based on the molecular dynamics (MD) simulations. The time history and maximum value of the sheet’s central point deflection are considered as two main indices and reported under various circumstances. The MD simulation has the ability to provide the time history and maximum value of the central deflection along with the vibration behavior of the GS under a moving nanoparticle. The effect of the sheet’s parameters, such as dimensions, surface tension, and boundary conditions, as well as the nanoparticle’s parameters, including dimensions and velocity, on the dynamic response of the sheet is studied. It was found that the velocity of the nanoparticle does not significantly affect the deflection of the GS, while the boundary conditions and aspect ratio of the sheet have a noticeable impact on the dynamic and vibrational behavior of the GS.

Low-velocity impact analysis of functionally graded porous circular plate reinforced with graphene platelets

ABSTRACT In this study, the low-velocity impact analysis of functionally graded (FG) porous circular plate reinforced with graphene platelets based on the first-order shear deformation theory is presented for the first time. The governing equations are derived using Hamilton's principle. A modified Hertzian contact law is used to model the contact force between the annular plate and the impactor. FEM approach in conjunction with the Picard method is employed to solve the governing equations of the plate under low-velocity impact. The results of the present study are compared with previous studies, and a good agreement can be seen between the results. The effects of different parameters such as porosity distribution and porosity coefficients, various GPL patterns and the weight fractions of Nano-filler on the contact force and transverse displacement of the circular plate are investigated. The results show that the effect of porosity distribution on the time history of contact force and transient central deflection of the structure is more than other parameters.

Dynamic fracture of glass fiber-reinforced ductile polymer matrix composites and loading rate effect

The dynamic fracture of S-2 glass fiber-reinforced polymer matrix composites (FRPMCs) was investigated in this study. The matrix ductility was improved by a recently developed network topology modification technique via mixing partially reacted substructures (mPRS). The composite material was manufactured and characterized by micro-CT scanning and scanning electron microscopy (SEM). Dynamic single-edge notched bending (d-SENB) experiments were performed on the composites by using a modified split-Hopkinson pressure bar. Each specimen's fracture process was visualized by ultrafast X-ray imaging. Such in-situ radiography enabled identifying the damage initiation below 50-μm scale and inspecting its propagation through the internal structures of opaque composites, thereby accurately quantifying the composites' mechanical properties. Furthermore, the identical d-SENB experiments were designed and the digital image correlation (DIC) was employed to monitor the stress wave propagation on the composite specimens . The force and deflection measurements were modified and correlated to the physical damage processes. Besides, quasi-static SENB experiments were conducted to identify the loading rate effects on the composites' fracture behaviors . The force and deflection history, bending stiffness , energy dissipation , and fracture toughness at different loading rates were quantified and compared. Finally, post-fracture analysis by micro-CT scanning and SEM provided physical observations on the variation of the fracture morphology at different loading rates.

The use of a two-phase Monte Carlo material model to reflect the dispersion of asphalt concrete fracture parameters

The work covers comprehensive laboratory tests of semi-circular bending (SCB) of asphalt concrete samples. The results of two test series, including four and 32 SCB specimens, indicate a substantial scatter of force–deflection (F-d) histories. The numerical analysis is aimed to reflect the maximum breaking load and fracture energy of the samples, pointing out their random character. The original simulation-based fictitious Monte Carlo material model was introduced. The authors’ algorithm randomly assigns asphalt mortar and coarse aggregate parameters to the finite elements of the numerical model. As a result, sets of random fields are generated to reflect the two-phase material distribution in the samples. The model parameters are numerically adjusted based on laboratory test results of the initial four SCB specimens. In the course of model verification, the 32-sample computations were compared with the laboratory data. The results of FEM simulations are consistent with laboratory test results, including dispersion of fracture parameters. The proposed computational algorithm with a two-phase material model is ready to be implemented in the analysis of actual road pavement constructions and may support the design process.

Renovation Effect of Flax FRP-Reinforced Cracked Concrete Slabs under Impact Loadings

The impact behaviour of flax fibre-reinforced polymer (FFRP) renovated coconut fibre-reinforced concrete (CFRC) slabs was investigated through two series of experiments and theoretical analysis. The first experiment was carried out to find out the effectiveness of FFRP retrofitted method for the partly damaged concrete structure and its performance under impact loadings. The renovation process was applied on the pre-cracked rectangular CFRC slabs of 600 mm × 300 mm × 50 mm with FFRP laminates, before the repeated impact tests. Then, the parameters of these slabs, i.e., impact force history, deflection history and damage pattern, were discussed in detail. Another experiment was conducted on the FFRP-CFRC square slabs with a dimension of 600 mm × 600 mm × 50 mm. Based on test results, the effect of different FFRP configurations was discussed to find out the effective reinforcement method. In addition, the two-degree-of-freedom spring-mass model was applied to predict the impact force. Results demonstrate that FFRP composites have a good potential to be utilised as renovated construction materials under dynamic load conditions.

Time-history blast response and failure mechanism of RC columns using Lagrangian formulation

Structural behavior of RC structures under explosive loads is an emerging field of research especially RC columns since the damage of RC columns can lead to progressive collapse. Most research works investigated and concentrated on the behavior of RC columns when exposed to far-field detonations (FFD). A limited study is available on the effects of near-field detonation (NFD) and close-in detonation (CID) on the behavior of RC columns. Hence, the main purpose of the current research is to investigate the influence of different types of detonation scenarios on the dynamic behavior of RC columns. The influences of extreme loading conditions on the columns are defined by using Lagrangian analyses in LS-DYNA. Validation of the numerical model is implemented by comparing the numerical analysis results with UFC 3–340-02 Standard. It is shown that the model yields a reliable prediction of damage on all RC columns. Intensive studies are performed to evaluate the influences of various scaled distances on the dynamic behavior of the columns. The results demonstrated that when the columns are subjected to CID explosions, they undergo the maximum pressure and the columns fail due to severe impulsive regime loading. The results revealed that when the scaled distance is in the CID range, the peak blast load increases but the duration of the positive phase of the blast wave decreases resulting in higher amplitude, lower-duration shock pulse and when the scaled distance is in the FFD range, the peak blast load decreases but the duration of the positive phase blast wave increases resulting in lower amplitude, longer-duration shock pulse. Also, the results show that increasing the scaled distance in RC columns subjected to NFD and FFD detonations resulted in a further decrease in the peak deflection histories and damage degree of RC columns in comparison to CID explosions. The current investigation and the outcomes can be utilized for evaluation of the effect of an explosion on the RC columns.

A strong coupling prediction-correction immersed boundary method

In the traditional immersed boundary methods for solving compressible fluid-structure interaction problems, conservation is one of the problems that must be considered. When the coupling boundary moves on the fixed grid, the structure coverage will change, resulting in many dead elements and emerging elements on the fluid grid. In the ghost-cell immersed boundary method, the reconstructed grid can not maintain the strict mass conservation when the dead elements and emerging elements appear. In order to overcome the shortcomings of traditional methods, a strong coupling prediction-correction immersed boundary method for compressible fluid-structure interaction problems was proposed. Firstly, the matrix representation of a general fluid-structure coupling system was described, and a strong coupling Gauss-Seidel iterative scheme of fluid-structure coupling system was derived. Furthermore, a prediction-correction scheme was derived, and a prediction-correction immersed boundary method was proposed. The fluid-structure coupling boundary was regarded as a free surface, and the space originally occupied by the solid was initialized as zero mass elements, allowing the fluid to pass through the coupling boundary freely. For the calculation of fluid, the second-order MUSCL finite volume scheme with the minmod limiter and the AUSM+-up flux based on Zha-Bilgen splitting were used to advance the time step with the third-order Runge-Kutta scheme. In the correction step, the transport process was realized by a set of mass conservation transport rules. The transport algorithm could be summarized as marking the fluid inside the boundary, dividing and moving the fluid in a uniform way according to the marking order, generating a flow pointing to the outside of the boundary, and finally applying a velocity correction near the boundary to ensure the no-slip condition. The marking and transport algorithm avoided the tedious geometric treatment of the cut-cells, and ensured the easy implementation of the algorithm. For the calculation of solids, the first-order difference scheme and the implicit dynamic finite element scheme were used to solve the rigid body and linear elastic body respectively, and the Gauss quadrature was used to obtain the coupling force on the solid surface. The one-dimensional and two-dimensional problems were calculated by the prediction-correction immersed boundary method. In the one-dimensional piston problem, the accuracy, conservation and convergence of the method were investigated by comparing the results with those in the literature. In the two-dimensional shock wave impact problem, the experimental optical schlieren images were compared with those obtained by the numerical simulation, and the deflection history of the plate structure was investigated. The study shows that this method can accurately maintain the mass conservation of the flow field and has the advantage of easy implementation, which is different from the traditional ghost-cell method and the cut-cell method. This method has the first-order convergence accuracy, and can accurately predict the flow field after shock diffraction and the deflection of plate under shock waves. It provides a new idea for the development of fluid-structure coupling algorithms.

Elastic impact of a spherical particle with a long, stationary, fixed Timoshenko beam

This study presents an analysis of the transient response of a beam subjected to transverse impact by a spherical particle. The beam is modeled as a long Timoshenko beam with clamped boundaries. A numerically stable solution to the dispersion relation is developed, which allows the deflection to include the effects of high-frequency waves. Time history of contact force, transverse deflection, velocity and acceleration provide insight into the interactions between the two objects after impact. Comparison with the Euler-Bernoulli beam model demonstrates the advantage of the Timoshenko beam in capturing the dispersive features of wave propagation. The group and phase velocities of bending waves due to impact are presented and show a good correlation with the time-domain analysis. The dependence of the coefficient of restitution on the mass ratio of the particle and the beam is discussed. Results show that the mass ratio divides the contact behavior of the particle and beam to a single-contact regime and multiple-contact regime and influences the coefficient of restitution (COR) value in different ways.

Experimental Study on the Damage of Steel Tubular Structural Components by Near-Field Detonations

This paper describes three blast-loading trials on three kinds of steel tubular structural components at the same explosive charge and standoff distance. Specimen one is a hollow steel tube (HST), another is a HST wrapped with glass fibre-reinforced plastic (GFRP) with epoxy resin and the third is a HST infilled with concrete. The main objective of the trials is to investigate the effect of near-field detonations on circular steel tubular components. The experimental data, such as the overpressure time history, front local deformation, rear residual deflection and strain time history, are all recorded and collected. Analysis of the trial results shows that the experimental peak overpressure values of shot 1–3 are all larger than that of numerical simulation. The failure of these three specimens mainly experiences local damage, at the same time, the HST and HST with GFRP exhibit obvious global deformation. With the initiation point at one end of the cylinder explosive, both the maximum depth deformation on the front surface and the maximum residual deflection on the rear surface are all located on the side of the another end of the cylinder explosive. The blast-resistant approach by covering 10-layer GFRP on the surface of the HST can reduce the local damage, the global deformation and the dynamic strain value to certain extent, while the approach by infilling the steel tube with concrete can greatly decrease the local damage and the dynamic strain value and without any global deformation.

Impact damage detection in CFRP and GFRP curved composite laminates subjected to low-velocity impacts

In this paper, the behavior of the CFRP and GFRP curved composite laminates under low-velocity impact loads is studied both numerically and experimentally. The time history of the mid-point deflection of the laminate along with the area of the damaged zone due to the impact are evaluated as two important indices of determining the behavior of the curved composite laminate under a low-velocity impact. In this regard, the active thermography damage identification technique and the image processing technology are employed to determine the pattern as well as the area of the damaged zone. In addition, the effect of the shape of the projectile nose on the behavior of the curved composite laminate is investigated by employing projectiles with flat, spherical, and conical noses with the same mass of 680 g.

Dynamic behaviors of reinforced NSC and UHPC columns protected by aluminum foam layer against low-velocity impact

Two strategies were proposed in this study to improve the safety of RC columns under low-velocity impact loading. One is setting up the protective closed-cell aluminum foam (CCAF) layer on the surfaces of RC columns for general structures, and the other one is utilizing the combination of the CCAF layer and UHPC for important structures. For verifying the effectiveness of these two strategies, both experimental and numerical investigations on the dynamic behaviors of reinforced normal strength concrete (R–NSC) and ultra-high-performance concrete (R–UHPC) columns protected by the CCAF layer against low-velocity impact were presented in this study. Two R–NSC columns and two R–UHPC columns were tested by the free-falling drop-weight system. The failure modes, failure process, time history of impact force and deflection were discussed in detail. Moreover, a 3D finite element model was developed to further investigate the impact dynamic behaviors of R–NSC columns and R–UHPC columns protected by the CCAF layer. The test results demonstrated that the CCAF layer can protect both R–NSC columns and R–UHPC columns effectively by reducing the impact force and absorbing a large amount of impact energy. Correspondingly, the safety of RC columns was also effectively improved since the impact force between the target and the impactor was reduced significantly by the adoption of the aluminum foam layer, and it verified strategy one. Furthermore, R–UHPC columns showed a better impact-resistant performance than R–NSC columns, especially, R–UHPC columns with the CCAF layer showed superior impact-resistant performance, and it verified strategy two. The finite element model can predict the dynamic behaviors of aluminum foam protecting R–NSC and R–UHPC columns with reasonable accuracy. Eventually, the energy absorption of the specimens was investigated by the numerical model.

Dynamic Large Deflection Response of RC Beams under Low-Speed Impact Loading

The dynamic large deflection response of RC beams under low-speed impact loading at their midspan is investigated in this paper. Two simple methods such as extended Hamilton’s principle and equivalent static hypothesis are used to establish the theoretical models for both simply supported and fully clamped RC beams; analytical formulas for the maximum midspan deflection-input impact energy are obtained. The “equal area” method based on the deflection history of beams is only used during these derivations to determine the plastic bending moment and the stress distribution of the structure. Then, finite element simulations are carried out to verify the validity of the proposed predictions. It is shown that the maximum deflections for both simply supported and fully clamped beams are almost proportional with respect to the input impact energy, which agrees well with both simulations and other experimental results. Also, the boundary condition has more effect on the deflection response of the RC beams which is relatively longer.