Displacement Curves Research Articles

Experimental and numerical study on the loading rate dependent tensile behavior of carbon fiber/epoxy interface

A series of experiments and simulations were performed to explore the effect of loading rate on the tensile behavior of carbon fiber/epoxy composite interface via the fiber bundle tensile method. Varying velocities were used to test the stress‒time and stress‒displacement curves of the samples, and a high-speed camera was used to study the in situ failure behavior of the carbon fiber/epoxy interface. Increasing the loading rate from 5 × 10−6 m/s to 12.0 m/s leds to an increase in the interfacial tensile strength from 6.1 ± 0.9 MPa to 16.4 ± 0.3 MPa, an increase in the interfacial stiffness from 1.58 ± 0.3 N/m to 17.4 ± 3.1 N/m, and a decrease in the fracture displacement from 0.23 ± 0.03 mm to 0.10 ± 0.01 mm. Optical microscopy analysis revealed rougher crack surfaces at higher loading rates. The fracture mode of interface transitioned from fiber breakage and pull-out to brittle matrix cracking with increasing loading rate. The finite element method was employed to verify the effectiveness of the fiber bundle tensile method with a split Hopkinson tension bar and study the failure behavior of the interface under dynamic loading. The simulation results showed that the calculated failure stress was 20 % lower than the actual value, and the cohesive layer was found to have greater stress at the edge region. This investigation deepens the understanding of the effects of the loading rate on the interfacial tensile behaviors of carbon fiber/epoxy composites.

Enhancing damage prediction in bulk metal forming through machine learning-assisted parameter identification

The open-source parameter identification tool ADAPT (A diversely applicable parameter identification Tool) is integrated with a machine learning-based approach for start value prediction in order to calibrate a Gurson–Tvergaard–Needleman (GTN) and a Lemaitre damage model. As representative example case-hardened steel 16MnCrS5 is elaborated. An artificial neural network (ANN) is initially trained by using load–displacement curves derived from simulations of a boundary value problem—instead of using data generated for homogeneous states of deformation at material point or one-element level—with varying material parameter combinations. The ANN is then employed so as to predict sets of material parameters that already provide close solutions to the experiment. These predicted parameter sets serve as starting values for a subsequent multi-objective parameter identification by using ADAPT. ADAPT allows for the consideration of input data from multiple scales, including integral data such as load–displacement curves, full-field data such as displacement and strain fields, and high-resolution experimental void data at the micro-scale. The influence of each data set on prediction quality is analyzed. Using various types of input data introduces additional information, enhancing prediction accuracy. The validation is carried out with respect to experimental void measurements of forward rod extruded parts. The results demonstrate, by incorporating void measurements in the optimization process, that it is possible to improve the quantitative prediction of ductile damage in the sense of void area fractions by factor 28 in forward rod extrusion.

A piece-wise linear model for modelling the tension-stiffening effect in steel-reinforced UHPC composites

This study examines the tensile behaviour of Ultra-High Performance Concrete (UHPC) specimens reinforced with varying steel fibre content and rebar diameters. An experimental campaign involving 18 reinforced UHPC specimens was conducted, following individual tensile response characterizations of UHPC and reinforcing steel. These specimens were designed and fabricated with threaded welded steel cages to transfer loads to the central measurement area. Force–displacement curves were measured to derive stress–strain curves for the UHPC component, evaluating the impact of reinforcement rebar and steel fibre content on UHPC’s mechanical response. The analysis revealed that steel fibre volume content significantly influences the tensile response of UHPC reinforcement more than the steel bar diameter and yield strength. Comparing the strain in steel bars to the average strain in reinforced UHPC specimens indicated that post-cracking deformation concentrates at the crack. At the same time, the bond between reinforcement and UHPC remains intact in uncracked sections, allowing effective load transfer. UHPC specimens reinforced with 14 mm diameter steel bars displayed a significant horizontal segment in the descending phase of the stress–strain curve. In contrast, specimens with 18 mm or 22 mm diameter bars exhibit a progressive stress reduction at a nearly constant rate. Stress–strain curves of UHPC were fitted with a five-fold piecewise empirical model applicable to UHPC with a reinforcement ratio higher than 0.09%. The resulting model can be used to model the axial behaviour in UHPC, considering the effects of steel reinforcement.

Research on Sea Trial Techniques for Motion Responses of HDPE Floating Rafts Used in Aquaculture

The innovative aquaculture equipment known as high-density polyethylene (HDPE) floating rafts has gained popularity among fishermen in the southeast coastal regions of China. Compared to deep-water anti-wave fish cages, the construction costs of HDPE floating rafts are 50% to 75% less. There is a dearth of comprehensive publicly available records of HDPE floating rafts sea trial data, despite substantial numerical studies on the motion response of aquaculture fish cages and scale model experiments under controlled-wave conditions. This study involves sea trial techniques under operational and extreme environmental conditions for motion responses of HDPE floating rafts, presents a comprehensive procedure for sea trials of HDPE floating rafts, summarizes the issues encountered during the trials, and suggests solutions. Using MATLAB for independent programming, motion videos and photos collected from the sea trials are processed for image capture, yielding the original time history curve of vertical displacement. Based on the sea trials’ data, including motion displacement, acceleration, mooring line force, overall deformation patterns, and current and wave data, recommendations are provided for the design and layout of HDPE floating rafts. Based on the Fast Fourier Transform (FFT) method for spectral analysis, the influence of interference items on the observational data is eliminated; the rationality of the observational data is verified in conjunction with the results of the Gabor Transform. This study offers a scientific analytical method for the structural design and safe operation of HDPE floating rafts and provides a reference for subsequent numerical simulations.

Finite Element Analysis of the Mechanical Response for Cylindrical Lithium-Ion Batteries with the Double-Layer Windings

The plastic properties for the jellyroll of lithium-ion batteries showed different behavior in tension and compression, showing the yield strength in compression being several times higher than in tension. The crushable foam models were widely used to predict the mechanical responses to compressive loadings. However, since the compressive characteristic is dominant in this model, it is difficult to identify distributions of the yield strength in tension. In this study, a simplified jellyroll model consisting of double-layer windings was devised to reflect different plastic characteristics of a jellyroll, and the proposed model was applied to an 18650 cylindrical battery under compressive loading conditions. One winding adopted the crushable foam model for representing the compressive plastic behavior, and the other winding adopted the elastoplastic models for tracking the tensile plastic behavior. The material parameters in the crushable foam model were calibrated by comparing the simulated force–displacement curve with the experimental one for the case where the cell was crushed between two plates when the punch was displaced by 7 mm. A specific cut-off value (10 MPa) was assigned to a yield stress limit in the elastoplastic model. Further, the computational model was validated with two more loading cases, a cylindrical rod indentation and a spherical punch indentation, as the punch was displaced by 6.3 mm and 6.5 mm, respectively. For three loading cases, deformed configurations and plastic strain distributions were investigated by finite element analysis. It was found that the proposed model clearly provides the plastic behavior both in compression and tension. For the crush simulation, the maximum compressive stress approached 222 MPa in the middle of the jellyroll, and the maximum effective plastic strain approached 60% in the middle of the layered roll. For indentation with the cylindrical and the spherical punch, the maximum effective plastic strain approached 52% and 277% in the layered roll, respectively. The local crack or location of a short circuit could be predicted from the maximum effective plastic strain.

An experimental study of a novel external fixator based on universal joints for the rapid initial stabilization of mandibular comminuted fractures

PurposeShaping and assembling contemporary external fixators rapidly for the severe mandibular fractures remains a challenge, especially in emergency circumstance. We designed a novel external fixator that incorporates universal joints to provide the stabilization for mandibular comminuted fractures. This study aims to confirm the efficacy of this novel external fixator through biomechanical tests in vitro and animal experiments. MethodsIn vitro biomechanical tests were conducted using 6 fresh canine with mandibular defect to simulate critical comminuted fractures. Three mandibles were stabilized by the novel external fixator and other mandibles were fixed by 2.5 mm reconstruction plates. All fixed mandibles were subjected to loads of 350 N on the anterior regions of teeth and 550 N on the first molar of the unaffected side. The stability was evaluated based on the maximum displacement and the slope of the load-displacement curve. In animal experiments, 9 beagles with comminuted mandibular fractures were divided into 3 groups, which were treated with the novel external fixation, reconstruction plate, and dental arch bar, respectively. The general observation, the changes in animals’ weight, and the surgical duration were recorded and compared among 3 groups. The CT scans were performed at various intervals of 0 day (immediately after the surgery), 3 days, 7 days, 14 days, 21 days, and 28 days to analyze the displacement of feature points on the canine mandible and situation of fracture healing at 28 days. The statistical significance was assessed by the two-way analysis of variance test followed by the Bonferroni test, enabling multiple comparisons for all tests using GraphPad Prism10.1.0 (GraphPad Inc, USA). ResultsThe outcomes of the biomechanical tests indicated that no statistically significant differences were found in terms of the maximum displacement (p = 0.496, 0.079) and the slope of load displacement curves (p = 0.374, 0.349) under 2 load modes between the external and internal fixation groups. The animal experiment data showed that there were minor displacements of feature points between the external and internal fixation groups without statistic difference, while the arch bar group demonstrated inferior stability. The CT analysis revealed that the best fracture healing happened in the internal fixation group, followed by the external fixation and arch baring at 28 days after fixation. The external fixation group had the shortest fixation duration (25.67 ± 3.79) min compared to internal fixation ((70.67 ± 4.51) min, p < 0.001) and arch baring ((42.00 ± 3.00) min, p = 0.046). ConclusionThe conclusion of this study highlighted the efficacy and reliability of this novel external fixator in managing mandibular fractures rapidly, offering a viable option for the initial stabilization of comminuted mandibular fractures in the setting of emergency rescue.

Design and validation of a novel 3D-printed glenohumeral fusion prosthesis for the reconstruction of proximal humerus bone defects: a biomechanical study.

All available methods for reconstruction after proximal humerus tumor resection have disadvantages, and the optimal reconstruction method remains uncertain. This study aimed to design a novel 3D-printed glenohumeral fusion prosthesis and verify its feasibility and safety using biomechanical methods. We verified the feasibility and safety of the 3D-printed glenohumeral fusion prosthesis by finite element analysis and biomechanical experimentation. In the finite element analysis, three reconstruction methods were used, and displacement and von Mises stress were observed; on this basis, in the biomechanical experiment, models constructed with sawbones were classified into two groups. The force‒displacement curve of the 3D-printed prosthesis was evaluated. In terms of displacement, the finite element analysis showed greater overall stability for the novel prosthesis than traditional glenohumeral joint arthrodesis. There was no obvious stress concentration in the internal part of the 3D-printed glenohumeral fusion prosthesis; the stable structure bore most of the stress, and the force was well distributed. Adding lateral plate fixation improved the stability and mechanical properties of the prosthesis. Furthermore, the biomechanical results showed that without lateral plate fixation, the total displacement of the prosthesis doubled; adding lateral plate fixation could reduce and disperse strain on the glenoid. The design of the 3D-printed glenohumeral fusion prosthesis was rational, and its stability and mechanical properties were better than those of traditional glenohumeral joint arthrodesis. Biomechanical verification demonstrated the feasibility and safety of this prosthesis, indicating its potential for proximal humerus bone defect reconstruction after tumor resection.

Numerical simulation and experimental investigation of resistance spot welding with initial gap under tensile shear load

In the resistance spot welding (RSW) process of body structures, the initial gap (IG) occurs frequently. The RSW with IG impact welding quality, and subsequently reducing the structural safety of the whole vehicle. An equivalent displacement method (EDM) is proposed, and a refined finite element model (FEM) is established to accurately simulate the mechanical responses of the RSW with IG under tensile shear loading. This research chose 3 IGs (0 mm, 3 mm and 5 mm) of RSW for investigation. First, a true stress-strain curve of base metal (BM) is obtained by uniaxial tensile test, and hardness of the 3 zone is obtained through hardness test. Then, the stress-strain curves of heat-affected zone (HAZ) and fusion zone (FZ) are fitted from those of BM based on relationship between Vickers hardness and tensile strength. Then, the refined 3D FEM of RSW with initial gaps are established based on EDM. Finally, the model is nonlinear analyzed and compared with the experiment. The results show that the force and displacement curves obtained through simulation are highly consistent with the ones obtained through experiments with the maximum mean integrated relative error (MIRE) is 7.42 %. The average error of the maximum load-bearing capacity is 1.05 %, and the maximum error is 2.58 %. The failure modes are both button pullout, attributed to the relatively low strength of BM. And cracks occur in BM near HAZ and penetrate along the sheet thickness direction. These findings show that numerical simulation of RSW with IG, based on the EDM, effectively reflects its mechanical properties and failure behaviors.

Numerical Modeling of Four-Pile Caps Using the Concrete Damaged Plasticity Model

Four-pile caps made from concrete are essential elements for the force transfer from the superstructure to piles or pipes. Due to the difficulties in carrying out full-scale tests and all the instrumentation involved, the use of numerical models as a way to study the mechanical behavior of these elements presents itself as a good alternative. Such numerical studies usually provide useful information for the update and improvement of normative standards and codes. The concrete damaged plasticity (CDP) constitutive model, which combines damage and plasticity with smeared-crack propagation, stands out in the simulation of reinforced concrete. This model is composed of five parameters: dilatation angle (ψ), eccentricity (ϵ), ratio between biaxial and uniaxial compressive strength (σbo/σco), failure surface in the deviator plane normal to the hydrostatic axis (Kc), and viscosity (μ). For unidimensional elements, the values of the CDP parameters are well defined, but for volumetric elements, such as concrete pile caps, there is a gap in the literature regarding the definition of these values. This fact ends up limiting the use of the CDP on these structural elements due to the uncertainties involved. Therefore, the aim of this research was to calibrate two numerical models of concrete four-pile caps with different failure modes for the evaluation of the sensitivity of the CDP parameters, except for ϵ, which remained constant. As a result, the parameters σbo/σco and Kc did not significantly influence the calibration of the force × displacement curves of the simulated structures. Values of ψ and μ equal to 36° and 1 × 10−4, respectively, are recommended for “static” analysis, while for “quasi-static” analysis, ψ values ranging between 45° and 50° are suggested according to the failure mode. The results also showed to be sensitive to the constitutive relation of concrete tensile behavior in both modes of analysis. For geometric parameterization, the “static” analysis is recommended due to the lower coefficient of variation (3.29%) compared to the “quasi-static” analysis (19.18%). This conclusion is supported by the evaluation of the ultimate load of the numerical models from the geometrically parametric study compared to the results estimated by an analytical model.

Atomistic Modeling of Quaternized Chitosan Head Groups: Insights into Chemical Stability and Ion Transport for Anion Exchange Membrane Applications.

The chemical stability and ion transport properties of quaternized chitosan (QCS)-based anion exchange membranes (AEMs) were explored using Density Functional Theory (DFT) calculations and all-atom molecular dynamics (MD) simulations. DFT calculations of LUMO energies, reaction energies, and activation energies revealed an increasing stability trend among the head groups: propyl trimethyl ammonium chitosan (C) < oxy propyl trimethyl ammonium chitosan (B) < 2-hydroxy propyl trimethyl ammonium chitosan (A) at hydration levels (HLs) of 0 and 3. Subsequently, all-atom MD simulations evaluated the diffusion of hydroxide ions (OH-) through mean square displacement (MSD) versus time curves. The diffusion coefficients of OH- ions for the three types of QCS (A, B, and C) were observed to increase monotonically with HLs ranging from 3 to 15 and temperatures from 298 K to 350 K. Across different HLs and temperatures, the three QCS variants exhibited comparable diffusion coefficients, underlining their effectiveness in vehicular transport of OH- ions.

Numerical analysis of underground displacements stirred by compaction grouting during tunnel construction

Compaction grouting is widely accepted to mitigate the surface settlements during tunnel excavation. Currently, compaction grouting relies heavily upon field observations due to the limit understanding of the amounts of soil displacements induced by a given volume of grout. In this study, parametric studies and probabilistic investigations are performed to examine the underground displacements caused by compaction grouting during tunneling. Under high injection pressure, soils flow around the center of a circle, which is approximately 2 m ∼ 2.8 m above the elliptical grouting bulbs and 3.3 m away from the far-end elliptical grouting bulb. An influenced zone, outside which effect of the burial depth of grouting bulbs can be neglected, is determined by connecting the intersections of vertical displacements curves. Influence of burial depth of elliptical grouting bulbs on vertical displacements is greater than that of the total length of elliptical grouting bulbs. When the total volume of elliptical grouting bulbs is identical, better grouting efficiency is achieved by increasing the volume of the elliptical grouting bulbs adjacent to the tunnel center, especially for deeper monitoring points. Locations of the maximum lateral displacements in soils are within a band underground. Moreover, probability of exceedance of vertical displacements on the tunnel center line and formulas describing the distributions of heaves in soils are presented for the benefit of assessing the project risk and liability and predicting the heaves in soils.

A Machine Learning Boosted Data Reduction Methodology for Translaminar Fracture of Structural Composites

AbstractThis work explored a machine learning (ML) algorithm as a fast data reduction method for translaminar fracture energy in composite laminates. The method was validated with translaminar fracture tests on compact tension (CT) specimens on AS4/8552 and IM7/8552 cross-ply lay-ups. Experimental fracture energy and R-curves for both materials were determined using the most common data reduction methods, such as the compliance calibration (CC), the area (AM) and the Irwin relationship (IM). Our new data reduction method uses a surrogate model based on an artificial neural network (ANN) trained with synthetic data generated with the cohesive crack finite element model. Such a surrogate model maps the cohesive properties with the corresponding load–displacement, crack-displacement and energy-displacement curves with interrogation times in the order of 20 ms and relative errors in the load–displacement and crack growth less than 2%. Such performance enabled its encapsulation to approximate the inverse problem to infer the cohesive parameters with the maximum likelihood estimator (MLE) directly from the experimental load–displacement and crack-displacement curves. The results demonstrated the ability of the model to deliver cohesive parameter inference directly from the macroscopic tests carried out at the laboratory level.

Processing and Mechanics of Aromatic Vitrimeric Composites at Elevated Temperatures and Healing Performance

Carbon fiber reinforced polymer (CFRP) composites are renowned for their exceptional mechanical properties, with applications in industries such as automotive, aerospace, medical, civil, and beyond. Despite these merits, a significant challenge in CFRPs lies in their repairability and maintenance. This study, for the first time, delves into the processing and self-healing capability of aromatic thermosetting co-polyester vitrimer-based carbon fiber composites through mechanical testing. Vitrimers are an emerging class of thermosetting polymers, which, owing to their exchangeable covalent bonds, enable the re-formation of bonds across cracks. The specific vitrimer chosen for this study is an aromatic thermosetting co-polyester (ATSP). The mechanical properties of samples were analyzed initially through three-point bending (3PB) testing at room temperature before and after healing (by curing samples for 2 h at 280 °C). Samples were also 3PB tested at 100 °C to analyze their mechanical properties at an elevated temperature for comparison to the samples tested at room temperature. To investigate the fracture properties, optical microscopy images of samples were taken after 3PB tests, which were analyzed to observe crack initiation and crack growth behavior. Through load–displacement curves from double cantilever beam (DCB) mechanical testing, the Mode I crack initiation fracture toughness values of self-healed composites and control composites were calculated to evaluate healing efficiency in ATSP CFRP composites cured at 280 °C for 2 h. Scanning electron microscopy (SEM) showed a similar surface morphology of cracks before and after self-healing. Micro-computed tomography (CT) X-ray imaging confirmed that the healed samples closely resembled the as-fabricated ones, with the exception of some manufacturing voids, caused by outgassing in the initial healing cycle. This research demonstrated the ability for the in situ repair of ATSP CFRPs by restoring the fracture toughness to values comparable to the pristine composite (~289 J/m2).

A nonlinear dynamic hysteresis model with magnetic–prestress–thermal coupling effect and dynamic electromagnetic losses of a giant magnetostrictive actuator

Compared with traditional actuators, the giant magnetostrictive actuator has the merits of fast response, high accuracy, and high reliability and has been widely applied. However, its performance is affected by the electromagnetic loss and the temperature, prestress, and magnetic coupling effect. In order to accurately analyze its performance, it is necessary to establish a nonlinear dynamic model including the electromagnetic loss and the magnetic–prestress–thermal coupling effect. First, based on the field separation approach, the magnetic fields generated by the eddy current loss and the anomalous loss are obtained and added to the Jiles–Atherton model. Second, the magnetostrictive model is given with the magnetic–prestress–thermal coupling effect. Finally, assuming the transmission of the giant magnetostrictive actuator as a mass–spring–damper system, a nonlinear dynamic hysteresis model with magnetic–prestress–thermal coupling effect and dynamic electromagnetic losses of a giant magnetostrictive actuator is developed. Based on this model, the output displacement curves of the giant magnetostrictive actuators under different driving currents and frequencies are given. The comparison with the experimental results shows that this model agrees well with the experiment.

Printing path-dependent two-scale models for 3D printed planar auxetics by material extrusion

One particularly interesting class of mechanical metamaterials are those having a negative Poisson’s ratio, which are referred to as ‘auxetics’. Because of their geometrical complexity, auxetic designs cannot always be easily created. However, Additive Manufacturing (AM) methods like material extrusion in 3D printing present the opportunity to construct auxetic structures. Nevertheless, extruded 3D printed material can be highly anisotropic. Before 3D printed auxetics manufactured through material extrusion can be used in engineering applications, it is important to generate powerful simulation tools that can reliably reproduce and foretell their mechanical characteristics irrespective of their form and intricacy. In view of this, the current work proposes printing path-dependent models based on an experimentally validated multi-scale modelling scheme using the Lattice Beam Model (LBM). This is done by first representing idealized microstructures of extruded 3D printed polymers through geometric models and simulating these on the material scale. The aim is to explicitly model the inter-layer and intra-layer bonds that exist in material extruded 3D printed parts by assigning experimentally obtained interface properties that significantly differ from the bulk material. On the auxetic structure scale, two planar auxetic designs are modelled using the determined material scale relationships as input: Re-Entrant (RE) and Rotating Square (RS). In terms of mechanical response, the experimentally and numerically obtained force displacement curves agree reasonably well: the stiffness of the modelled auxetic designs fit well with the experimentally measured ones while the LBM simulations generally provide a good estimation in strength. Finally, it has been shown on both the material and auxetic structure scales that incorporation of the interfacial bond strengths in simulations of extruded 3D printed polymers is important, because neglecting these results in significant overestimation of the strength.

Experimental Study on Fracture Toughness of Shale Based on Three-Point Bending Semi-Circular Disk Samples

A large number of construction practice projects have found that there are many joints and microcracks in rock, concrete, and other structures, which cause the complexity of rock mechanical properties and are the main cause of geological or engineering disasters such as earthquakes, landslides, and rock bursts. To establish a rock fracture toughness evaluation method and understand the distribution range of fracture toughness of Longmaxi Formation shale, this study prepared three-point bending semi-circular disk shale samples of Longmaxi Formation with different crack inclination angles. The dimensionless fracture parameters of the samples, including the dimensionless stress intensity factors of type I, type II, and T-stress, were calibrated using the finite element method. Then, the peak load of the samples was tested using quasi-static loading, and the load–displacement curve characteristics of Longmaxi Formation shale and the variation in fracture toughness with crack inclination angle were analyzed. The study concluded that the specimens exhibited significant brittle failure characteristics and that the stress intensity factor is not the sole parameter controlling crack propagation in rock materials. With an increase in crack inclination angle, the prefabricated crack propagation gradually transitions from being dominated by type I fracture to type II fracture, and the T-stress changes from negative to positive, gradually increasing its influence on the fracture. An excessively large relative crack length increases the error in fracture toughness test results. Therefore, this paper suggests that the relative crack length a/R should be between 0.2 and 0.6. The fracture load distribution range of shale samples with different crack angles is 3.27 kN to 10.92 kN. As the crack inclination angle increases, the maximum load that the semi-circular disk shale samples can bear gradually increases. The pure type I fracture toughness of Longmaxi Formation shale is 1.13–1.38 MPa·m1/2, the pure type II fracture toughness is 0.55–0.62 MPa·m1/2, and the T-stress variation range of shale samples with different inclination angles is −0.49–9.48 MPa.

Coupled effects of UV radiation and freeze–thaw cycles on the fracture behavior of asphalt concrete

The Qinghai-Tibet Plateau in China is characterized by extreme climate conditions, including intense ultraviolet (UV) radiation, frequent freeze–thaw cycles (FTCs), and significant temperature fluctuations. These conditions contribute to severe cracking in asphalt pavements. This study aims to investigate the impact of coupled damage from UV radiation and FTCs on the fracture behavior of asphalt concrete. To simulate the coupled environmental damage (CED) experienced by asphalt pavement in the field, an alternating two-factor laboratory procedure was developed. This procedure reflects the climatic conditions of the Qinghai-Tibet Plateau. The semi-circular bending test, combined with digital image correlation technology, was employed to evaluate the effects of temperature and CED cycles on fracture-related parameters of asphalt concrete. These parameters include the load–displacement curve, fracture toughness, and fracture energy. Fracture behavioral characteristics such as horizontal strain, crack length, crack propagation path, and crack mouth opening displacement were also analyzed. The results indicate that coupled damage from UV radiation and FTCs significantly weakened the fracture resistance of asphalt concrete. Compared with other fracture-related indicators, the most significant reduction observed was the fracture energy of 68.1%. The two environmental factors exhibited a mutually reinforcing effect on the fracture properties of asphalt concrete, with low temperatures further intensifying their influence. CED cycles delayed the initiation of cracks in asphalt concrete but accelerated crack propagation. This led to a reduction in time to failure by up to 57.6% and a maximum reduction in horizontal strain of 24%. Additionally, the cracking propagation path of asphalt concrete became more linear with increased crack mouth opening displacement. Future research should focus on the evolution of damage accumulation in asphalt concrete under CED cycles, with the goal of establishing predictive models for long-term service life.

Comprehensive design strategy of the NSD–TMD controlled system with closed-form frequency-amplitude solutions

A negative stiffness device (NSD) utilizing pre-compressed helical springs has been integrated with diverse vibration control techniques. Recently, the incorporation of NSD has been proposed to enhance the efficacy of a tuned mass damper (TMD) controlled system. This study introduces two design strategies for the NSD–TMD system, which functions either as a TMD with an adjustable operating bandwidth or as a pure non-linear energy sink. First, the non-linear force of NSD was expressed in a Taylor series approximation form incorporating a negative linear stiffness and a positive cubic stiffness term. Second, the equations of motion were formulated, and closed-form solutions were derived using the complexification–averaging method. The accuracy of the Taylor series approximation was substantiated within a specified range through a comparison of force–displacement curves. Third, the accuracy of the dynamic closed-form solutions was affirmed by comparing the amplitude–frequency curves with the numerical simulations. For a case study, an actual timber pedestrian bridge with decaying natural frequency was selected, and the two design strategies were examined individually. The vibration control performance of the TMD and NSD–TMD was also comparatively analyzed. The assessment focused on the peak force transmissibility value and the effective operating frequency bandwidth. Results highlighted a notable enhancement in operational performance, particularly for primary structures exhibiting diminishing modal frequencies. In a TMD-controlled system, the efficacy of vibration control deteriorates and may even amplify the dynamic response when a modal frequency shift occurs in the primary structure. Conversely, both design strategies of NSD–TMD can achieve lower transmissibility and broaden the operating bandwidth.

Investigation of the bedding effect on coal rock under Brazilian splitting tests

This contribution focuses on understanding the bedding effect of coal rocks under the Brazilian splitting test. First, multiple Brazilian splitting tests were performed on coal rocks with various bedding angles to systematically investigate the influence of stratification. Subsequently, numerical models with stratified structures were constructed, and a continuous–discontinuous numerical analysis method based on the cohesive zone model (CZM) was employed to conduct the corresponding numerical investigations. Results indicate that the load–displacement curves of coal rock specimens with different bedding angles can be classified into four stages: initial compaction stage, elastic deformation stage, crack rapid coalescence stage, and final destruction stage. With increase in the bedding angle, the failure patterns of coal rock specimens can be categorized into three groups: 1) stretching damage along bedding planes; 2) mixed tension and shear failure along the bedding planes and the coal matrix; and 3) stretching failure passing through the coal matrix. Furthermore, the tensile strength and cumulative acoustic emission (AE) energy–displacement relations are significantly influenced by the bedding angle. The numerical model can effectively predict the mechanical responses and fracture behavior of coal rock specimens, providing empirical parameters for the simulation of similar rock engineering.

Fast analysis approach for instability problems of thin shells utilizing ANNs and a Bayesian regularization back-propagation algorithm

Abstract This research develops a data-driven methodology for structural instability problems with highly nonlinear, difficult, noisy, and small data. A fast analysis and prediction (FAP) approach for instability problems of thin shells is first proposed. This approach contains two phases: the fast numerical analysis and the pure prediction utilizing artificial neural networks (ANNs) incorporated with the Bayesian regularization (B-R) algorithm as follows: (1) in Phase 1 (the fast numerical analysis), post-buckling analysis is conducted utilizing a minor amount of load steps. The load–displacement relation achieved from Phase 1 is not exact because of the small number of load steps utilized; (2) in Phase 2 (the prediction), the loads and deflections achieved from Phase 1 were employed as the data for training ANNs. The trained networks, including the load and displacement networks, were employed to fast predict loads and deflections at any step of the post-buckling analysis. After utilizing Phase 2, a smooth, complete and exact load–displacement curve was achieved. In Phase 1, the available formulation for post-buckling analysis of thin shells in the literature was utilized. Five popular types of instabilities chosen to confirm the effectiveness and exactness of the FAP were snap-through, snap-back, softening–hardening, kink instabilities, and delamination buckling and post-buckling of composites. The high exactness and effectiveness of the FAP were confirmed in the numerical verification section. The present approach saves a huge computation compared to the other ones. It was found that ANNs incorporated with the B-R algorithm have notable advantages compared to numerous neural networks. The proposed approach is applicable to simulations or experiments where data are “expensive”, highly nonlinear, difficult, and limited. Utilizing the proposed approach for these fields can dramatically save time and money.