Interlayer Damage Research Articles

Mechanical properties of basalt/jute fiber composites to improve the phenomenon of drawing delamination

AbstractIn recent years, natural fibers have been commonly used to reinforce various polymers, resulting in composites with excellent mechanical properties. To address the challenge of delamination and significant fiber pull‐out in inter‐laminar hybrid composites during stretching, this study focused on preparing intra‐laminar hybrid textile composites using basalt fibers (BFs) and jute fibers (JFs) as raw materials. Moreover, the mechanical properties of BF/JF intra‐layer blended fabric composites were investigated. The prepared composites underwent tensile, flexural, impact, and dynamic mechanical analysis (DMA). The results indicated that intra‐laminar blended composites demonstrated superior mechanical properties compared to inter‐laminar blended fabric composites. The DMA results revealed that the intra‐laminar blended composites featured a high peak loss factor. Morphological analysis indicated enhanced stress transfer from fiber‐to‐fiber and fiber‐to‐matrix in the intra‐laminar blended composites.Highlights Fiber blending can expand the application areas of natural fibers. Fiber blending can reduce interlayer damage. Intra‐layer blending differs from interlayer hybrid composites. Strong bonding between fibers facilitates effective stress transfer. “Green” composites exhibit exceptional mechanical properties.

Low‐velocity impact resistance of the Z‐pin reinforced carbon fiber composite laminates

AbstractA voronoi user material subroutine (VUMAT) was developed using the three‐dimensional Hashin damage criterion and exponential nonlinear damage evolution method. An interlayer damage model based on the quadratic nominal stress (QUADS) criterion and B‐K fracture criterion was introduced, and a finite element model of Z‐pin reinforced composite laminates under low‐velocity impact was established. The low‐velocity impact behavior of Z‐pin reinforced composite laminates with different impact velocities (0.6 m/s, 0.4 m/s, and 0.3 m/s), different layup forms ([0°/90°]4 and [0°/45°/90°/−45°]2), and different Z‐pin spacing (4 mm, 8 mm, and 16 mm) was studied using ABAQUS. The results indicate that different layup forms have little effect on the low‐velocity impact behavior of Z‐pin reinforced composite laminates. The Z‐pin spacing has a significant influence on the low‐velocity impact behavior of Z‐pin reinforced composite laminates. When the impact velocity is 0.4 m/s, the specific energy absorption of composite laminates with Z‐pin spacing of 16 mm is 85.93% and 87.7% lower than that of composite laminates with Z‐pin spacing of 4 mm and 8 mm. As the Z‐pin spacing decreases (Z‐pin density increases), the impact resistance of Z‐pin reinforced composite laminates first increases and then decreases.Highlights• The low‐velocity impact of Z‐pin reinforced composite laminates was studied.• Analyzed the effect of layup forms of laminates on their impact behavior.• Explored the influence mechanism of Z‐pin spacing on the impact behavior.• Studied the energy absorption of different Z‐pin spacing under impact velocity.

Detection of ballastless track interlayer gap based on vehicle’s multivariate dynamic response and deep learning

To adapt to the rapid detection of interlayer damage in ballastless track structures of high-speed railways, a cement asphalt mortar (CAM) gap localization and damage degree classification scheme based on multivariate data fusion and deep learning is proposed. Based on vertical axle box acceleration (VABA) and vertical wheel-rail force (VWRF) data, the variation patterns of multi-dynamic response data of vehicles under the edge type and internal type interlayer gaps are analyzed. An improved ensemble local mean decomposition algorithm (IELMD) is designed to achieve data denoising and preliminary enhancement preprocessing of weak damage features for VABA and VWRF under interlayer gaps. The measured and simulated VABA and VWRF constituted multiple dynamic response data sets for interlayer gap detection. An interlayer gap detection model: DTA-Tcnformer is constructed, integrating a dual temporal convolutional network with an attention mechanism, transformer architecture, and gate control mechanism. Multiple dynamic response data are input into the model to locate and classify 24 cases of the two interlayer gap types. The influence of damage cases and vehicle speeds on the location effect is analyzed. The learning ability of the proposed model on the gap features is visualized. The misidentification and omission of the gap cases are calculated, and the comprehensive recognition accuracy is 92.48 %. The recognition performance of the proposed model is compared and verified.

Study on the causes of interface damage of CRTS II slab ballastless track CA mortar based on grouting operation

In this work, the relationship between cement asphalt mortar (CAM) grouting operation and interface damage of CRTS II slab ballastless track was explored. The test method for the time-varying viscosity of CAM during the solidification process was optimized, and the curves of the time-varying viscosity of CAM at different temperatures were obtained through experiments. A generalized time-varying viscosity constitutive model with CAM temperature and time as parameters was constructed. A fluid dynamics model to simulate CAM grouting operation based on finite element method was established, which could take into account the time-varying viscosity of CAM. The influences of various grouting parameters on the interface state were analyzed with the dynamics model. The results show that the correlation coefficients between the time-varying viscosity constitutive model and the test results are greater than 0.96. It is verified that the CAM grouting operation is an important cause of interlayer damage. The time-varying viscosity of CAM is beneficial in reducing the area of the interface damage zone caused by CAM grouting operation. The area of the interface damage zone decreases with the reduction of the distance between the end vent and the end of prefabricated slab and the rise of grouting temperature. When the height of the prevent vortex grille cylinder is close to 0.4 m, the vortex effect at the position of the grouting hole can be effectively controlled, and the area of the interface damage zone can be significantly reduced.

The role of the fiber–matrix interface in the tensile properties of short fiber–reinforced 3D‐printed polylactic acid composites

AbstractIn this study, we investigate the relationship between structure and properties of fiber–matrix adhesion for material extrusion–based 3‐dimensional (3D) printed composites. We examine the influence of fiber length and fiber content on the tensile properties of glass, basalt, and carbon fiber–reinforced polylactic acid (PLA) composites. Short fiber–reinforced filaments were produced, then, simple micromechanical models were used to predict the in‐plane tensile properties. We found that interlayer tensile properties are strongly influenced by fiber–matrix adhesion. If adhesion is sufficient, the fibers and matrix deform together under tensile load. A second‐order relationship describes interlayer tensile strength in relation to fiber content between 5 and 25 w%, with a maximum at 15 w%, for carbon and basalt fiber–reinforced composites. If adhesion is weak, the crack propagates along the fiber–matrix interface, causing brittle fracture and low strength. This behavior was noted for the glass fiber composite, for which the calculated interface shear strength was the lowest (1.4 MPa). In this case, fiber content is inversely proportional to interlayer tensile strength. Our results show the role of fiber–matrix adhesion quality on tensile properties, which has a major impact on both the accuracy of predictions and the damage processes.Highlights Critical fiber length determines accuracy of tensile property estimates Quality of fiber–matrix adhesion governs interlayer damage process Poor adhesion causes brittle fracture and low strength Second‐order relationship of interlayer tensile strength and fiber content Loss of interlayer tensile strength in composite due to fiber–matrix interface

Open Hole Tensile Behaviour of Sisal-Glass Reinforced Epoxy Composite

Research and development in engineering composites are advancing rapidly. The demand for lightweight materials with high specific strength in aerospace and high-energy applications makes composites a prime choice. Using composite materials to reduce structural weight is favored for energy saving and emission reduction, making them popular in automobiles and other fields. However, composites require holes for assembly and fastening in many applications, such as airplane structures and automotive parts. These holes can concentrate stress, potentially reducing tensile strength and compromising structural integrity. Notches, including holes and slots, are inevitable during assembly and may also result from impact damage during service. Ensuring safety and reliability necessitates quantifying residual properties and failure responses. Stress concentration issues will occur around holes, whether in laminates used for interior decoration, outsourced parts, or bearing components. Therefore, notch design must consider the effects on failure mode, mechanical performance, and interlayer damage distribution. This study examines the open-hole tensile behavior of sisal-glass fiber-reinforced epoxy composites, aiming to understand the impact of circular holes on their tensile strength and failure mechanisms.

Interlayer damage evolution of CRTS III slab track under passenger and freight train loads

To study the interface damage in CRTS III slab tracks under the concurrent interactions of temperature and mixed passenger and freight train loads, a refined fatigue cohesive zone model (F-CZM) considering the stiffness, strength, and energy fracture degradation factors was presented. Utilizing this model, a finite element model (FEM) of the CRTS III slab track was developed. The interface fatigue damage between the track slab and self-compacting concrete (SCC) under various adhesive strengths and mixed operation modes was calculated. The interface characteristic degradation and stress change of door-type steel bars were revealed. Results show that good performance is ensured within the design service life with intact interface adhesion. The interface damage develops from the slab corner to the edge and then into the inner. The diminished interfacial tangential adhesive strength causes two patterns of interfacial damage procession. Enhanced freight train ratio escalates interface damage. During the development of interface damage, the door-type steel bars act as a safety margin.

Effect of blind-bolt repair method on vibration and compression characteristics of delaminated composite aircraft panels

The paper investigates the validity and reliability of the blind-bolt repair method for repairing delaminated composite aircraft panels. The delaminated specimens are prepared by inserting Teflon films during the manufacturing process to simulate interlayer damage. Subsequently, these specimens are repaired using the blind-bolt method. Modal and uniaxial compression tests are conducted to quantitatively evaluate the natural frequency, mode shape and load-bearing strength of both delaminated and bolt-repaired specimens. Digital image correlation and ultrasonic phased array techniques are employed to characterize buckling instability and damage evolution of specimens. The results reveal that the natural frequency and compressive buckling strength of delaminated specimens significantly decrease. The mode shape also changes nonlinearly with the stiffness reduction. This variation is proportional to the size and the quantity of delaminations. The blind-bolt repair method effectively restores the vibration and mechanical properties of the delaminated composite structure by reconnecting separated sub-laminates. A repair tolerance of 20 mm–60 mm is recommended for a single blind-bolt. When the delamination length is 35 mm, the repair efficiency for the critical buckling load and the ultimate load is the highest, at 58.3% and 64.4%, respectively.

Fracture behavior investigation of ballastless track of high-speed railway based on DIC technique

To investigate the issues of transverse through cracks and interlayer damage of the CRTS III slab ballastless track under train loading, the digital image correlation (DIC) technique was employed to reveal the damage mechanisms of the reduced-scale concrete of track slab structural concrete (TSSC) and track slab-filled laminated structural concrete (TSLSC). The results indicate that under train loading, the transverse through cracks of TSLSC exhibit a multi-stage, layer-by-layer cracking characteristic, and there is a risk of cracking in ballastless track when the bottom longitudinal strain exceeds 0.0004. The sudden increase in interlayer longitudinal shear strain difference in the third stage under train loading demonstrates that shear stress is the primary cause of interlayer damage in ballastless track. Tensile damage models based on ultimate stress–strain relationship and yield-fracture strain were established, and a non-contact testing method for the constitutive relationship and energy absorption effect of ballastless track was proposed using DIC technology, aiming to provide reference for the analysis and prediction of ballastless track damage under train loading.

Evolution Mechanism of Interlayer Properties of CRTS III Slab Track during Construction

The interlayer properties of the CRTS III slab track during construction directly affect its long-term service condition. This article introduces time-varying coefficients that characterize the early properties of the interface between track slab and SCC to improve the bilinear CZM. Based on this, an interlayer property evolution model of the CRTS III slab track during construction is established. The evolution mechanism of interlayer properties under complex loads and the influence mechanism of key parameters on them are revealed. The results show that after SCC pouring, the interlayer damage at the corner of the slab becomes a sensitive area due to the combined effects of SCC shrinkage and temperature gradients. Interlayer damage initially manifests at the corner of the slab before progressively spreading toward the center of the slab, influencing the composite performance and force transmission characteristics of the track structure. The interlayer bonding property, shrinkage performance of SCC, and construction temperature substantially affect interlayer damage evolution. To reduce the risk of damage, mineral admixtures and expansion agents can be added as additives to improve the bonding property and minimize shrinkage of SCC. Insulation measures should be taken for SCC during low-temperature construction, and SCC pouring construction below 0 °C and above 30 °C should be avoided.

Non-coincident contact deformation behavior between double-block ballastless track interlayers under normal load

Interlayer damage presents a substantial challenge in ballastless tracks, impacting their operational performance. In order to assess the contact deformation at the interfaces between concrete layers, normal loading tests were conducted on the non-coincident contact between rough interlayer surfaces of a double-block ballastless track. A contact model was developed that considers elastic, elastoplastic, and plastic deformations. The study established the relationship between normal load and contact area, and derived a formula to calculate normal deformation stiffness. The results indicate that: I) the model effectively simulates normal contact deformation behavior between layers; II) during loading, the normal load increases non-linearly with displacement, while minimal elastic recovery deformation is observed during unloading; III) the composite rough interface morphology is the most crucial parameter influencing contact deformation behavior; IV) the relationship between normal load and contact area is linear. Additionally, the normal deformation stiffness is positively correlated with the nominal contact area, contact area stiffness, and the value of the rough interface point cloud height distribution function at the corresponding deformation. The presented elastoplastic contact model and deformation stiffness calculation method contribute to understanding the operational performance of ballastless tracks following interlayer cracking.

Bimodulus constitutive models and the simulation on bending properties of woven carbon fibre-reinforced composites

The tensile and compressive properties of woven carbon fibre-reinforced composites (CFRP) are different owing to the buckling and entanglement of fibre bundles. Two bimodulus constitutive models (TBM and PBM) were proposed based on the track stress criterion and principal stress criterion. Combined with the Hashin three-dimensional strength criterion and Alvaro stiffness reduction criterion, a material subroutine was written to calculate the bimodulus constitutive models. Three-point bending tests of [0/90]20 and [±45]20 were designed to obtain the load–displacement curves and failure modes. The precision of the calculation results with the traditional unimodulus model and bimodulus models were compared, and the bending performance of woven CFRP was explored. The results demonstrate that fibre fracture and interlayer damage occur with different stacking sequences. The material properties can be better shown with less error as bimodulus models. The stiffness and strength of the PBM were slightly larger than those of the TBM, and the failure factors were smaller than those of the TBM. The results of the TBM are closer to the test, and the material subroutine is easier to realise. Bimodulus constitutive models have good application prospect in woven composites for higher accuracy.

Combined RVE-Cohesive elements approach to the multi-scale modelling of FDM 3D-printed components

Mechanical strength of 3D-printed components dramatically depends on printing process parameters. These can be usually set over a relatively wide range, in combinations that determine the microstructure morphology and the resulting mechanical behaviour. The present investigation focuses on the relationship between revealed structure and resulting mechanical properties of FDM-printed ABS specimens. The peculiar structures, examined at the meso- and microscale, are modelled by a finite-element Representative Volume Element (RVE) approach, in conjunction with cohesive elements to reproduce the sealing efficiency between fused filaments. The simulation of the tensile response up to failure falls within the 95% of confidence with experiments. Also, homogenized response of RVE determines spatial material constants useful for the effective numerical simulations of functional components, and intra- and inter-layer damage mechanisms are distinguished providing hints for the structural optimization.

Fatigue damage propagation of FRP under coupling effect of cyclic load and corrosion

AbstractInterlaminar fracture or delamination is one of the major failure modes for fiber reinforced polymer (FRP) laminate. Especially, the synergistic effect of environmental exposure and fatigue loads accelerates interface degradation. The main objective in this work was to investigate the fatigue damage propagation of basalt FRP (BFRP) laminate under coupling of acidic environment and fatigue load. The fatigue cycling of 40,000 and the maximum stress of 30% fu (fu = ultimate tensile strength) were adopted. The fatigue specimens under air condition (air fatigue), immersing in water (water fatigue) and immersing in acid (acid fatigue) were introduced. The double cantilever beam (DCB) test was used to evaluate the interlaminar damage of BFRP laminate after fatigue cycling. The fatigue damage propagation mechanism was explored by means of failure modes, load displacement curves, mode I fracture toughness and crack propagation resistance model. The results show that the fatigue weakened the interlaminar properties and resulted in reduced fiber bridging. Especially for the acid fatigue, the laminate was damaged by the coupling of fatigue and acid corrosion. The linear loading stage, nonlinear slow growing stage, stable crack propagation stage and linear unloading stage for DCB after fatigue were observed in the load–displacement curve. The fatigue cycling has caused fracture toughness decrease of 15.0%, 13.8% and 24.1% on air fatigue, water fatigue and acid fatigue respectively. Compared to air fatigue, additional 9.1% interlaminar toughness decrease was evidenced for acidic corrosion fatigue due to the coupling effect of chemical corrosion and physical swelling. The fluctuating decline of crack resistance was caused by discontinuous interface damage, and the interlayer damage was randomly distributed. Thus the interface damage model was proposed to characterize the damage distribution and the damage size.Highlights Degradation law of BFRP under the coupling effect of acid immersion and fatigue load. Interface damage model for characterization of the damage distribution and damage size. Fatigue damage propagation of BFRP under coupling effect of cyclic load and corrosion.

Adhesion performance tests and analysis of interface damage for CRTS III prefabricated slab tracks

Debonding between the track slab and self-compacting concrete (SCC) is a common form of damage in China railway track system (CRTS) III prefabricated slab tracks. To investigate the influence of interlayer cohesive parameters on the interface connection, composite specimens of track slabs and SCC were made to be used for splitting tensile and shear tests. The variation characteristics between the interface’s tension and displacement were obtained using digital image correlation (DIC) techniques, and the key parameters of a cohesive zone model (CZM) were determined and used to simulate the cracking behavior. Also analyzed was the interlayer damage behavior of the composite specimen using ABAQUS, the results of which were compared with those of the tests. Furthermore, a finite element simulation model of the CRTS III prefabricated slab track with CZM was used to analyze the impact of different cohesive parameters on interlayer damage under train loads and varying temperature gradient loads. The results show that: I). The DIC technique accurately describes the entire process from the damage initiation and propagation, to complete failure of the interface-bonded components; II). The finite element simulation results of the concrete composite specimens agree with the experimental results, indicating the CZM accurately reflects the interlayer cracking behaviors; III). Reducing the interface stiffness and increasing the critical fracture energy can slightly delay the onset of interface damage and debonding, respectively; IV). An increase in the cohesive strength can effectively inhibit the development of interface damage, for example, increasing the normal and tangential cohesive strength can improve the starting temperature gradient for interlayer damage initiation by 150 % and 45 %, respectively; and V). Under large positive temperature gradients (>70 °C/m), the interlayer debonding rate corresponding to most cohesive parameters reaches 100 % (complete failure of adhesion), making extreme temperature areas a necessary focus on the interlayer debonding of slab tracks. The research results of this paper can be used to analyze the damage behavior between the track slab and SCC layer, and provide a theoretical basis for the design and maintenance of CRTS III prefabricated slab track.

Thermal–mechanical coupling numerical simulation and low damage analysis for drilling composite

In this paper, a progressive damage analysis model of thermal–mechanical coupling dynamic response and damage evolution for composite under the drilling thrust and friction force is established based on elastic dynamics, heat conduction and damage criterion. Then the thermal–mechanical coupling model of low damage strategy for drilling composite by support metal is established, and the thickness of the support metal is considered. Further, a quantitative evaluation method of composite damage during drilling process is proposed and the quantitative evaluation of matrix damage and interlayer damage is realized. At last, the mechanism and influence for supporting structure to reduce the damage during the drilling process is analyzed by means of thrust force, torque, temperature and damage.

Time-variant reliability of interlayer damage of CRTS-II slab track by combining the second-order fourth-moment and outcrossing method

This study proposes the combining second-order fourth-moment and outcrossing method for evaluating the time-variant reliability of slab tracks’ interlayer damage. The merit of the method is to improve significantly the computing efficiency and accuracy for the implicit and strong nonlinear limit state function. Furthermore, the effects of narrow joints damage and temperature load on the time-variant reliability of slab tracks’ interlayer damage are investigated. Narrow joints damage is an inducement for the decrease of time-variant reliability index of slab tracks’ interlayer damage, and the index decreases more violently with the increase of temperature rise than that of positive temperature gradient.

Incompatible thermal deformation of interlayers and corresponding damage mechanism of high-speed railway track structure

In the service period, the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers. The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers, leading to a considerable difference in the force bearing of different structure layers. Unit Ballastless Track Bed (UBTB) is most significantly affected by temperature gradient. The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient, resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail. When the train travels on the periodically irregular rail, the structure layers are locally contacted, and the contact zone moves with the variation of the wheel position. This wheel-followed local contact greatly magnifies the interlayer stress, causes interlayer damage, and leads to a considerable increase in the bending moment of the track slab. Continuous Ballastless Track Bed (CBTB) is most significantly affected by the overall temperature variation, which may cause damage to the joint in CBTB. Under the combined action of the overall temperature rise and the temperature gradient, the interlayer damage continuously expands, resulting in bonding failure between structural layers. The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab, and the loss of constraint boundary of the horizontal stability. For the design of a ballastless track structure, the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.

Numerical simulation of temperature field of CRTS III ballastless track with Tarmac in Harbin area

The three-dimensional transient thermal analysis technology of ABAQUS is used to analyze the temperature field and temperature stress characteristics of CRTS Ⅲ ballastless track with thin layer of asphalt concrete under the typical climatic conditions of summer and winter in seasonal freezing area due to the influence of heat transfer such as solar radiation, wind speed and temperature amplitude. The results show that the temperature distribution of track structure is nonlinear along the vertical direction, and there is a lag phenomenon; After adding asphalt concrete layer, the temperature of Subgrade under the layer is reduced, which has a good heat insulation effect; Asphalt concrete layer is more prone to interlayer damage in winter than in summer.

Mechanical behavior of bonded interface between steam-cured concrete and SCC under direct shear test: Experimental and numerical studies

The interlayer damage of slab ballastless track for high-speed railway has become a weak link that affects the safe operation of track structure. Under the combined action of the train self-weight load and wheel-rail friction, the track plate presents complex stress state. Meanwhile, the interlayer defects and bond state have a great influence on the damage mechanism of track plate. The failure mechanism of concrete-concrete interface under combined stress has been focused on, but it is still not well quantitatively investigated at the grain scale. In this paper, the discrete element method (DEM) combined with digital speckle and acoustic emission monitoring technology is used to conduct the direct shear tests on bonded samples composed of steam-cured concrete and self-compacting concrete (SCC) with different bond interface characteristics. On this basis, it is quantitatively analyzed the effects of interfacial bond strength and interfacial morphological characteristics on the compressive-shear mechanical properties and damage patterns of bonded samples, and the deterioration mechanism of the interface is explained from a mesoscopic perspective. The results show that the compression-shear mechanical response and damage features of the bonded samples are the result of the combined effect of bond strength and morphological characteristics of the interface. The increase of bond strength makes the samples change from shear cracking damage along the interface to tensile cracking damage inside the concrete. The bonded area ratio (BAR) of the interface maintains a good positive linear correlation with the shear strength, and the increase of BAR makes the brittle failure more obvious in the post-peak stage. The increase of interface roughness coefficient (IRC) makes more compressive stress concentration areas form in the interface, which enhances the shear strength of the bonded sample to a certain extent.