Damage Modes Research Articles

Effect of geometric configurations and curvature angle of corrugated sandwich structures on impact behavior

AbstractThe aim of this study is to numerically investigate the low‐velocity impact behavior of carbon fiber reinforced orthogonal woven fabric composite sandwich structures with five different geometric configurations and four different curve angles. Low velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of core configuration and curve angle on peak contact force, energy absorption efficiency and damage mode. A progressive damage analysis based on the combination of the Hashin damage criterion and the Cohesive Zone Model (CZM) with bilinear traction‐separation law was performed using the MAT‐54 (ENHANCED_COMPOSITE_DAMAGE) material model. Among the five different cores, Trapezoidal core has the highest peak force average of 2.9 kN while Triangular core sandwich structure has the lowest with 1.23 kN. Absorbed energy efficiency average was highest for rectangular core with 0.95 and lowest for sinusoidal core with 0.69. The specific absorbed energy value was highest for Triangular core with 0.312 J/g and lowest for Sinusoidal core with 0.178 J/g. The damage area on the structure increased with increasing curve angle. It was determined that the core structure and curve angle is an effective parameter on peak force and energy absorption efficiency.Highlights Impact behavior of sandwich composite structures was examined. The effects of core type and curve angles on peak force, energy absorption efficiency and specific absorption energy were investigated. Specific absorption energy rates were compared with studies in the literature.

Experimental investigation on low‐velocity impact performance of carbon fiber reinforced polyether ether ketone thermoplastic composite materials in room and elevated temperature

AbstractCarbon fibers woven‐ply reinforced polyether ether ketone (C/PEEK) thermoplastic composites are widely used in aerospace and high‐tech industries because of their exceptional resistance to low‐velocity impact. In this paper, experimental investigation is carried out to determine the low‐velocity impact performance of C/PEEK laminates at room temperature (RT) and high temperature (90°C and 150°C) environments. Both macroscopic and microscopic analyses are applied to examine the influence of temperature on the mechanical response and damage mode of the material. The attention of this investigation is on impact parameters such as maximum contact force, energy absorption rate, indentation depth, and damage mode. The findings show significant changes in material stiffness, rate of energy absorption, and indentation depth with rising temperature. Temperature variations have a notable effect on the PEEK matrix plasticity, C/PEEK composite interlaminar properties, crack initiation and propagation, and damage mode at the overlaps of warp and weft fibers, resulting in a transition from brittle to ductile failure.Highlights Experimental investigation is carried out to study the low‐velocity impact performance of C/PEEK. The effects of impact energy and environmental temperature on the low‐velocity impact performance of C/PEEK are investigated. The mechanism of how environmental temperature affects the damage mode of C/PEEK is investigated.

Acoustic emission and multiscale computation-guided tensile damage identification in woven composite laminates at cryogenic temperatures as low as 20 K

For laminated composite structures as key components of storage tanks serving at cryogenic temperature, it is crucial to identify the damage mechanisms for evaluating their mechanical properties and guiding structural design. In this work, the cryogenic tensile damage behavior of a thin-walled woven composite laminate was investigated through the acoustic emission (AE) monitoring and multiscale finite element (FE) computation at typical low temperatures of 153 K, 77 K and 20 K. We first established temperature-dependent constitutive laws for the microscale and mesoscale constituents of such composites based on experimental data, followed by the development of a hierarchical computational framework for modeling multiscale damage characteristics at different low temperatures. A fiber-optic acoustic emission measurement system was constructed to provide online monitoring of tensile damage of the woven composite laminates at cryogenic temperatures as low as 20 K. The comparations were made between the predicted cryogenic damage characteristics and in-situ AE signal analysis, assisted by scanning electron microscope (SEM) observations. The computed cryogenic damage evolution closely matched the AE signal identification results. The results indicate that fiber breakage and matrix cracking are the dominant cryogenic damage modes, and that the different low temperatures exert significant effects on the properties of the epoxy matrix, yarns and composite laminates. The combination of the AE monitoring system and the computational scheme provides a valuable tool for evaluating structural integrity and guiding the microstructural design of composite laminates used in cryogenic environments.

Influences of fiber orientation and process parameters on diamond wire sawn surface characteristics of 2.5D Cf/SiC composites

2.5D Cf/SiC composite materials are widely used in aerospace high-temperature components, optical system structural components and other fields due to their excellent performance. For the cutting of 2.5D Cf/SiC composites, diamond wire saw cutting process has great potential for application. In this study, experiments were conducted on cutting 2.5D Cf/SiC composites with diamond wire saw along different fiber orientations (P0°, P90°, V90°) and different process parameters. The effects of fiber orientation, feed speed, and wire speed on the surface morphology, surface waviness profile, and roughness of the as-sawn surface were analyzed. The results show that fiber orientation significantly affects the fiber damage mode and surface quality of the as-sawn surface, with the surface quality of the slices ranked as V90°>P0°>P0°. The surface morphology and surface roughness improves with decreasing feed speed and increasing wire speed. However, surface waviness profile peak-valley (PV) values increases with increasing the feed speed and wire speed. The study provides experimental references for process optimization and quality improvement in diamond wire saw cutting of 2.5D Cf/SiC composite materials.

Enhanced LaRC05 failure criteria for investigating low-velocity impact on fiber-reinforced composites: An experimental and computational study

A finite element model was developed using both continuum and discrete damage modeling techniques to provide detailed predictions for ply-by-ply damage progression in composite laminates during low-velocity impact (LVI) events. A new fiber failure model was incorporated into the LaRC05 failure criteria to predict fiber pull-out and fiber crushing during the fiber damage evolution. In addition, the selective range golden section search (SRGSS) algorithm was implemented to efficiently predict fiber breakage, pull-out, splitting, kinking and crushing, and matrix cracking. The delamination was captured by cohesive element layers embedded between every adjacent composite ply. The interactions of intralaminar matrix cracking and delamination were modeled by deploying cohesive elements within each composite ply. The prediction results were validated by 30 J and 75 J drop-weight tests with different-sized impactors, as well as X-Ray CT inspections on 254 mm by 304.8 mm [0/45/90/-45]4s IM7/977–3 laminates. The model predicted the maximum deflection and contact duration with <2 % error, and the peak load, damaged areas, and absorbed energy with <8 % error. The matrix fracture plane and the fiber kink band angle were found with 1° precision 48 % faster via the SRGSS algorithm. The detailed sequences of damage occurrence were predicted by analyzing the energy dissipation histories through various damage modes. Although this modeling methodology was developed for LVI scenarios, it has broad applications for predicting failures in composites.

Optimization study of strengthened T-shaped concrete-filled steel tubular (CFST) column-steel beam joint

In this paper, a strengthened T-shaped concrete-filled steel tubular (CFST) column-steel beam joint is proposed. The joint is strengthened in the core region of the column wall as well as the beam, to avoid buckling of the column wall and outward displacement of the plastic hinge at the beam end. To study the damage modes and seismic performance of the joint, low-cycle loading experiments on two full-scale specimens of the joint were carried out. The results show that each specimen was damaged by plastic hinging of the steel beam flanges, the column walls did not buckle, and all had a good seismic performance. In addition, Abaqus finite element software was utilized to optimize the joints by analyzing the effects of changing the dimensions of the strengthened column and modifying the structure of the beam-column connection. Simulation results show that increasing the thickness and height of the strengthened column wall enhances the joint's load capacity, stiffness, and energy dissipation. it is recommended that the width-to-thickness ratio of the strengthened columns should be at most 0.08 and the beam-to-column height ratio should be kept at least 1.3. Additionally, two optimization methods, reducing the wall thickness of the steel corbel and weakening the steel beam flange, can effectively reduce weld tearing at the beam-to-column connections, while guaranteeing a good seismic performance. It is suggested that the slope of the steel corbel is not less than 1:6.25, and the weakening ratio of the steel beam flange is not greater than 0.267.

A study of the seismic resistance performance of strengthened masonry walls using polypropylene mesh-composite on the surface

To investigate the seismic performance of masonry walls in village buildings strengthened with polypropylene mesh materials on the surface, five reduced-scale masonry walls were designed for low-cyclic reversed loading tests. The research observed the failure processes and characteristic forms of masonry walls, conducting a comparative analysis of the hysteresis curves and energy dissipation of the walls. Then, ABAQUS finite element software was used to simulate the performance of the strengthened walls to analyze the damage mode of these walls. The results indicated that under compression-shear loading, unreinforced masonry walls experienced shear failure along horizontal mortar joints, exhibiting lower shear load, lateral stiffness, and ductility. The reinforced walls with polypropylene mesh-composite effectively delayed and mitigated the failure. Weak zones in the wall gradually extended from the structural sides towards the central core area. Ultimately, after the reinforcement material had fully engaged, delamination failure occurred, leading to the formation of "X" or "Y" shaped through cracks. After reinforcement with single-side polypropylene materials, the load-bearing capacity of the wall increased by 165 % compared to the unreinforced wall. The ductility is improved compared to the unreinforced wall, whereas the initial stiffness increased by 133 %. Upon reinforcement with double-sided materials, the wall's load-bearing capacity surged by 180 %. The initial stiffness climbed to 171.3 %. The finite element analysis results closely aligned with the experimental data, suggesting that reinforcing the surface with polypropylene mesh-composite cement mortar significantly bolstered the wall's shear strength and deformation capabilities. This method effectively strengthens the seismic resistance of masonry structures.

Microstructural behavior of CNT-PDMS thin-films for multifunctional systems

Heterogeneous ribbed and non-ribbed carbon nanotube (CNT)-PDMS thin-film systems manufactured by large-scale rolling exhibit large-strain and high strain-rate characteristics with favorable surface behaviors, such as superhydrophobicity and drag reduction. However, it is not well understood how the multi-phase microstructure and material properties of non-ribbed thin-films are related to the surface material behavior and fracture. Hence, the objective of this investigation is to characterize the large-strain mechanical behavior and the microstructure of various CNT-PDMS compositions to understand how the CNT loading, agglomeration, distribution, and orientation affect the mechanical behavior and fracture of CNT-PDMS unribbed systems. Non-ribbed thin tensile testing specimens were fabricated for neat PDMS and CNT-PDMS with different weight CNT distributions to understand non-ribbed behavior. The ultimate strain, strength, and global stress–strain behavior were obtained by uniaxial mechanical testing. Scanning electron microscopy (SEM) of the fracture surface was also obtained for each sample to analyze the microstructure and relate the damage mode to the different weight distributions. Based on these experimental measurements and observations, large-strain, hyperelastic and hyper-viscoelastic material models were used to characterize the material behavior. The hyper-viscoelastic material model was shown to provide the most accurate material description of the thin-film behavior of the viscoelastic PDMS with the high-strength CNTs.

Multi-scale analysis of ultimate bearing capacity in composite hull joints: failure mechanism and numerical simulation

ABSTRACT Progressive failure analysis method is the main method to analyse the ultimate bearing capacity and failure mode of composite structures. Multi-scale method can effectively reduce the dependence of damage mode and stiffness degradation analysis on material parameters. Based on the multi-scale method, from micro-scale to mesoscale and then to macro-scale, the equivalent modulus and equivalent strength of fibre bundles, single-layer laminates and multi-directional laminates were predicted respectively, and the prediction method of ultimate bearing capacity of large-scale composite structures from material level to structure level was constructed. The mechanical properties of standard composite materials and the ultimate bearing capacity of full-scale composite joints were tested respectively, and the ultimate bearing capacity and failure mode of L-joints were predicted by numerical method. The results show that the numerical simulation method based on multi-scale can accurately predict the ultimate bearing capacity and failure mode of large-scale joints of the hull.

Experimental and numerical investigation of arch concrete slabs subjected to underwater contact explosions with the inner arch side facing air

Arch structures with their inner arch side exposed to air and outer arch side exposed to water are often encountered in practical projects, and these engineering structures may be subjected to various explosive attacks during operation. This paper investigates the damage mechanism and dynamic response of arch concrete slabs with the inner arch side facing air against underwater contact explosions (UWCEs). The explosion tests of the arch concrete slab with the inner arch side facing air were carried out. The accuracy and applicability of the numerical model were verified by comparing with the explosion results. After that, the failure evolution and energy transition of the arch concrete slab with the inner arch side facing air were studied. The effects of different explosion masses, explosion distances, and reinforcement schemes on the antiknock performance of arch concrete slabs are further explored. The results show that as the explosive mass of UWCEs increases, the damage mode of the arch concrete slab with the inner arch side facing air changes from cracking along the longitudinal direction and local failure to spalling on the inner arch side and fragmentation of the contact specimens. The existence of curvature of the arch slab will cause the damage of the arch slab to intensify. The failure mode of the arch concrete slab changes from local failure to slight failure with cracks as the explosion distance increases. Increasing the longitudinal steel bars on the outer arch side can effectively inhibit the generation and development of cracks.

Different DNA Binding and Damage Mode between Anticancer Antibiotics Trioxacarcin A and LL-D49194α1.

Trioxacarcin A (TXN) is a highly potent cytotoxic antibiotic with remarkable structural complexity. The crystal structure of TXN bound to double-stranded DNA (dsDNA) suggested that the TXN interaction might depend on positions of two sugar subunits on the minor and major grooves of dsDNA. LL-D49194α1 (LLD) is a TXN analogue bearing the same polycyclic polyketide scaffold with a distinct glycosylation pattern. Although LLD was in a phase I clinical trial, how LLD binds to dsDNA remains unclear. Here, we solved the solution structures at high resolutions of palindromic 2″-fluorine-labeled guanine-containing duplex d(A1A2C3C4GFGFT7T8)2 and of its stable LLD and TXN covalently bound complexes. Combined with biochemical assays, we found that TXN-alkylated dsDNA would tend to keep DNA helix conformation, while LLD-alkylated dsDNA lost its stability more than TXN-alkylated dsDNA, leading to dsDNA denaturation. Thus, despite lower cytotoxicity in vitro, the differences of sugar substitutions in LLD caused greater DNA damage than TXN, thereby bringing about a completely new biological effect.

Investigating the simulation test and acoustic emission characteristics of structural-control type rockbursts in deep underground environments

Deep underground projects are in a complex in-situ stress environment, and rock burst disasters induced by the hard and brittle failure of the rock mass are prone to occur around the tunnel openings. In this study, we aim to investigate the impacts of geological weak surfaces in rock masses on rockbursts and the spatiotemporal evolution of microcracks during the development of rockbursts. To achieve this objective, two sets of cubic specimens containing a circular through-hole were designed. One set of specimens had prefabricated unfilled cracks around the openings. Subsequently, the rockburst development process within the deep tunnel was replicated by subjecting both groups of specimens to identical gradient loading using a true triaxial test system. During the test, a micro camera was used to record the failure of the borehole wall in real-time, and an acoustic emission monitoring system was utilized to capture the stress waves released during structural damage. Finally, a multi-level synergistic analysis of the rockburst damage mechanism was carried out based on the macro-imaging data and micro-acoustic emission data. The results show that failure in high-stress environments within tunnels mainly includes microcrack initiation, particle ejection, crack propagation, local cracking, slabbing spalling, damage penetration, and rockburst damage. The time–frequency domain information of acoustic emission signals is highly perceptive and representative of the structural damage state of the specimens. The mutation characteristics observed in time-domain parameters, such as acoustic emission amplitude, event rate, ringing, and cumulative energy, correspond to drastic alterations in the internal structure of the rock. The distribution characteristics of frequency-domain parameters, such as acoustic emission peak frequency, dominant frequency energy, and frequency centroid, reflect different crack scales and damage modes. The diffusion of frequency centroid indicates that the damage and failure patterns within the rock are evolving towards a more complex direction. The energy magnitude of acoustic emissions represents the damage intensity during the development of rockburst. The root causes of induced structural-control type rockbursts in deep hard brittle rock masses are the combined effects of localized high-stress concentrations and large-scale discontinuous geological structures, such as natural joints, fissures, and structural planes. The naturally occurring large-scale through-type geological weak surfaces within the rock mass reduce the strength of the surrounding rock, alter the location of stress concentration, and change the initial damage characteristics. Moreover, they promote the evolution of rockbursts, thereby increasing their destructive intensity.

Effects of high temperature and strain rate on the impact-induced inter-laminar shear behavior of plain woven CF/PEEK thermoplastic composites

This paper aims to investigate the interlaminar shear properties and failure mechanisms of plain woven carbon fabric/polyetheretherketone (CF/PEEK) thermoplastic composites under high strain rate impact loads at different temperatures (25°C, 120°C, 295°C). A reliable hot air flow heating method with SHPB is creatively employed for short beam shear experiments. A multi-scale model was developed to predict the impact behavior of plain CF/PEEK composites. Both results show that the thermoplastic composites have strong strain rate and temperature dependence, and which are more sensitive to temperature effect. As the temperature increases, the thermoplastic composites are mainly affected by the softening effect of the matrix due to the glass transition temperature. The shear modulus and peak stress appear to decline at high temperatures, while the failure strain tends to increase. The damage mode changes from interlayer delamination cracking at the glassy state to shear fracture and fiber pullout at a highly elastic state. As the strain rate increases, the failure strain decreases, while the shear modulus and peak stress show the opposite trend. Fiber bundle breakage, debonding, matrix cracking, and significant interlayer delamination occur at high strain rates.

Low velocity impact resistance of hybrid CFRP‐elastomer‐metal laminates: Influence of stacking sequence and impact conditions on damage mechanisms

AbstractFiber‐metal laminates (FMLs) are generally regarded as excellent lightweight materials for advanced structure design. To enhance the mechanical properties, the common FMLs can be optimized using carbon fibers. However, the combination of carbon fibers with aluminum induces interfacial challenges. Preventing galvanic corrosion with elastomeric interlayers is an effective solution. The lay‐up configuration greatly effects the impact damage resistance of hybrid CFRP‐elastomer‐metal laminates (HyCEMLs). In this work, micro‐CT scans and optical micrographic inspections on HyCEMLs are conducted after impact tests to ascertain the microstructural origins behind the mechanical performance changes. In addition, finite element models of different HyCEML configurations are built to complement the limited experimental data. The damage mechanisms of HyCEML with different configurations under various impact conditions are further compared. The numerical results suggest that impact energy is a more informative measure in terms of damage mode and size than impact velocity and momentum. Results also indicate that when the thickness for each sub‐laminate of HyCEML is maintained the same, hybrid laminates with aluminum stacked outside is beneficial for delaying the occurrence of matrix cracking and delaminations, and enhances HyCEML's resistance to global deformation. These findings will contribute to engineering hybrid laminates with desired impact performance for lightweight load‐bearing structures.Highlights The hybrid laminate with elastomeric interlayers is a forward‐looking solution in impact applications. Impact energy is a more informative measure in terms of assessing the damage mode and extent in HyCEMLs. The influence of stacking sequence on damage mechanisms of HyCEMLs is evaluated. Microstructural origins behind variations of hybrid laminates in the impact resistance are revealed.

Hybridization effect of Kevlar and glass fiber on carbon/epoxy composites to enhance the damage strength under low velocity impact. Part II: Numerical simulations

The research outlined in this paper extends the authors previous work to explore the impact resistance enhancement of CFRP composites through numerical simulations, focusing on the incorporation of a hybrid combination of Kevlar and glass fibers. Experimental drop weight low velocity impact and advanced NDT tests on CFRP and hybrid laminates were carried out in previous work. The current work focuses on the analysis of the dynamic behavior of hybrid composite subjected to LVI by numerical simulation methods. The numerical simulations have been validated with experiments and the damage area of numerical and experimental tests were compared. CFRP and hybrid laminates were modeled using Abaqus/Explicit FEA software to investigate the damage modes and mechanisms. The history curves of simulation results such as load/displacement-time etc. compared with experimental. Results show that incorporating 25% Kevlar fibers on the outer layer of the CFRP, denoted as [01K/06C/01K] resulted in a reduction of laminate deflection by 63.64%. Additionally, the stress distribution expanded over a larger area. A good concurrence between the simulation and experimental findings has been established, indicating that the modeling approach is suitable for conducting further parametric investigations.

Seismic behavior and design of concrete-filled steel tubular frame-RC core tube structures

In the design of frame-core tube structures, the method for adjusting the frame bearing capacity and stiffness to ensure the structure as a dual system is a critical issue. This study investigates the effects of frame shear distribution ratio, frame bearing capacity, and column pattern on the seismic performance of concrete-filled steel tubular frame to reinforced concrete core tube structures (CFRCTs). Time-history and seismic fragility analyses on eight representative models are performed and the distribution pattern of inter-story drift ratios, structural damage modes, and collapse safety margins are compared. The study results show that CFRCTs possess superior seismic performance (with a collapse margin ratio > 9.3) compared to the structures with reinforced concrete columns and the collapse margin ratio continuously increases from 9.3 to 11.2 with increasing frame stiffness. Enhancing the frame bearing capacity mitigates the frame damage, while improving slightly on structure’s collapse resistance (< 0.1 %). Without adjusting the frame for the second fortification line, damage to the column is not serious and the frame can still effectively withstand the increased shear force transmitted from the core tube during an extremely severe earthquake. The frame experiences more shear force and damage as the frame shear distribution ratio increases; while the core tube damage is effectively alleviated. Due to the redistribution of internal forces, the distribution pattern of inter-story drift ratios under the collapse state is markedly distinct from that under the elastic stage and severe earthquakes. Based on the analysis, design suggestions considering both collapse resistance and economic efficiency are proposed for CFRCTs.

Refined analysis of a supporting column assembly in a traditional Tibetan timber building and its limiting tilt angle before collapse

Traditional Tibetan architecture is an important part of the Chinese architecture. Many of the Tibetan structures are suffering from different types of damages after hundreds of years of service. The structural arrangement, types of damage and failure modes of these timber structures have been investigated on site. Tilting of structural members is found to be the most common type of damage. This paper studies the limiting inclination angle of a single-column supporting assembly of these structures before its collapse for proactive maintenance and restoration. A method to estimate the limiting tilt angle of the column is proposed based on the relationship between the lateral force, F, at the column head and the tilt angle, θ, of the column. Simplified analytical models of this column assembly in a traditional Tibetan timber building under in-plane and out-of-plane loadings respectively are proposed. The behavior of the constituting column foot joint, column-Queti joint and Queti-beam joint are analyzed in detail to obtain the global deformation and M-θ relationship of the column assembly under different loads. The F-θ relationship of the column assembly from the intact state to collapse is then obtained. A verified finite element model of the column assembly is adopted as reference to validate the performances of the proposed models throughout the loading process. Comparison of the F-θ curves obtained from the analytical models and the simulated results demonstrates the validity and accuracy of the proposed models. They may be adopted for a quick analysis of practical structures to estimate their limit states for health monitoring, maintenance and strengthening of structures.

Investigation on rock damage associated with ice-filling borehole blasting

Rock excavation and ore extraction in cold regions (e.g., alpine and high-altitude regions) are often conducted using the drill and blasting method. Ice may be presented in boreholes drilled in cold regions due to the potential freezing of water (e.g., water in rock fractures and pores) flowing into boreholes from the surrounding ground. The performance of rock blasting is inevitably affected by the presence of ice and no study has examined the effect of ice in boreholes on rock blasting performance. The present study investigates rock damage induced by the ice-filling borehole blasting. The damage modes and mechanisms of rock mass under the ice-filling borehole blasting are analyzed. The differences of rock damage induced by the sole ice-filling borehole blasting and the ice-water and ice-air mixed filling borehole blasting are identified. The effects of ice volumes in boreholes on blast-induced rock damage are examined. It is found that blast-induced rock damage is greatly reduced as water in boreholes turns into ice. In addition, the blasting with the ice volume greater than 6.7 % filled at the bottom of borehole can induce less rock damage compared to full-coupled charge blasting. To improve the performance of rock blasting with ice-filling boreholes, the effects of two methods, i.e., changing ignition locations and using different types of explosives on rock damage induced by the ice-filling borehole blasting are investigated. An empirical formula of rock damage volume incorporating ice volume, explosive properties, and rock properties is finally proposed as the reference for the design of ice-filling borehole blasting in cold regions.

Extreme temperature influence on low velocity impact damage and residual flexural properties of CFRP

AbstractIn this work, the behavior of carbon fiber reinforced polymer composites (CFRPs) interleaved with electrospun veils under low velocity impact (LVI) conditions and extreme environmental temperatures was investigated. 2/2 twill carbon fiber/epoxy laminates were subjected to LVI at three energy levels (10, 20, and 30 J), and three temperatures (−50°C, room temperature, and 100°C). Two interleaved configurations were explored (six veils placed symmetrically with respect to the middle plane of the laminate and with respect to the external layers of the laminate). Particularly at room temperature and up to 20 J, nanofibrous interlayers effectively reduced localized deformation (by about 13.0%) and delamination (by about 12.2%) when positioned in the outer ply interleaved configuration compared to the reference laminate. At 100°C, this effect is maintained at 10 J, preventing an increase in the delaminated area. At −50°C and 10 J, the promotion of delamination prevented back surface fiber failure. Regarding post‐impact flexural properties, the presence of nanoveils ensured superior mechanical properties compared to the corresponding reference laminate impacted at the same conditions, demonstrating their efficacy in enhancing the damage tolerance of the overall laminate.Highlights Electrospun veils were interleaved in 20 layers of 2/2 twill carbon/epoxy laminate. Three configurations were tested under LVI at 10 J, 20 J, 30 J, and −50°C, RT, and 100°C. Observed damage modes include delamination, indentation, and back surface fiber cracks. Veils symmetrically placed in external layers limit delamination at 20 J (RT) and 10 J (100°C). Electrospun veils enhanced CFRP bending and residual post‐impact properties at RT and 100°C.

Centrifuge tests study on settlement and damage modes of bridge approaches using deep-seated slab

The issue of bridge end bumps is a critical concern in the failure of bridge and bridge approaches. A series of novel centrifuge tests utilizing a ring model box were conducted to investigate settlement and its induced damages at the bridge approach. A new mitigation method, the deep-seated slab, for bridge end bumps was modeled in the test. This study analyzed the decisive role of pavement stiffness, soil modulus, and load cycles on deformation from the perspective of structure-soil interaction under standard traffic load conditions. The test results show that when deep-seated slabs are used, the deformation of the bridge approach follows an exponential decay pattern, eventually stabilizing after approximately one slab length. Furthermore, the upper and lower bridges exhibit distinct damage modes, i.e., the bridge damage by wheel collision at the upper bridge and the pavement damage by wheel impact at the lower bridge. The damage zone on the pavement is approximately 1.7 times the wheel width and the damage zone on the bridge 2.6 times. Finally, a predictive model for the deformation of bridge approaches was proposed, considering the effect of pavement stiffness, subgrade soil modulus, and load cycles. The relationship between the deformation and the three normalized variables conforms to the quadratic polynomial function in matrix form.