Damage Modes Research Articles

Finite element analysis of fibre reinforced timber beams under flexural loading

ABSTRACT Laminated Veneer Lumber (LVL) is a popular product used in the building and construction industry because of its high strength, serviceability, aesthetic characteristics, and cost-effectiveness. However, LVL has traditionally been limited to residential and small light commercial buildings. To expand the use of LVL and reduce the need for steel and reinforced concrete structural members, a comprehensive computational study is conducted to understand the material’s structural performance and find an optimal strengthening ratio. In this paper, a new 3-dimensional Finite Element model was introduced and evaluated to predict the structural behaviour, strength properties, and failure damage modes of LVL timber beams reinforced with a Carbon Fibre Reinforcement Polymer (CFRP) sheet. The model is validated with three experimental tests from the literature, with the reinforced timber model showing a 1.8% error compared to the plain timber model’s 7% error. Additionally, a parametric study is conducted to understand the effects of reinforcement length on the structural behaviour of the reinforced beam, with mathematical equations established to express the relationships. The study found that reinforcing 50% of the beam span generally resulted in the most significant strength improvement. This investigation is made for various strength and serviceability parameters.

Rolling Element Bearing Damage in the Presence of Applied Electric Current

Modern wind turbines and battery electric vehicles have bearings in close proximity to electrical generators, motors, and inverters. These systems have motivated new research focused on damage mechanisms associated with low- and high-level electric currents in rolling element bearings. This work presents a study on the influence of applied electric current and lubricant selection on bearing surface damage. Direct current was applied to a rotating tapered roller bearing with axial load and oil lubrication. Tests were conducted with various levels of applied current and two different oils (additized and non-additized). Micropitting, white etching cracking (WEC), and the formation of a surface white layer were investigated using both optical microscopy and scanning electron microscopy. Some of the tested bearings had black oxide surface treatment on their rollers and raceways. The black oxide was evaluated with regard to the prevention of the WEC damage mode. The occurrence of the described damage modes depended on the type of oil used and the application of electric current. Higher electric currents increased bearing surface damage in these tests.

Bolted connections in prefabricated cantilevered cap beam-column structures: A comprehensive experimental and numerical study

Prefabricated cantilevered beam-column structures have gained popularity in mountainous road construction. However, a notable research gap exists regarding the beam-column connections. To fill this gap, a new bolted connection method was introduced for the cantilevered beam-column structure. The mechanical performance of this novel structure was systematically investigated through reduced-scale experiments and finite element analysis. The structure's response under three critical loading conditions was experimentally examined, revealing the efficacy of bolted connections in preserving structural integrity and highlighting pronounced strain concentration at the connection region of the cap beam. Furthermore, to enhance structural design, a finite element model of this beam-column structure was established to simulate the influence of various materials and structural parameters on structural response and damage. Simulation results indicated that the anchor rod angle and the number of bolts had a minor impact on load-bearing capacity and damage modes. In contrast, the choice of concrete material and steel reinforcement ratio significantly influenced load-bearing capacity. The insights derived from this study offer valuable guidance for optimizing and extending the application of this structural design.

Effects of Reverse Fault Dislocation Application Method for Tunnelling Through Active Faults

Active faults seriously threaten the structural integrity of mountain tunnels in seismic zones, and reverse faults are the most hazardous. A tunnel project in the western region was used as a reference to analyze the damage mechanism of tunnels under different modes of reverse fault displacement. The ABAQUS finite element analysis software was employed for the numerical simulation, and a quasi-static method was adopted to analyze the displacement and stress response patterns of the tunnel structure traversing the fault under three typical modes of reverse fault displacement. This led to deriving the tunnel structure’s longitudinal damage modes and impact zones based on reverse fault displacement. The study revealed that the damage modes of the tunnel under different fault displacement modes varied, which was reflected in the different degrees of shear and compression. Regardless of the fault displacement mode, the tunnel structure located within the fault fracture zone was severely damaged, with the most severe damage occurring at the interface between the fixed plate and the fault displacement section. Therefore, in the design, special attention should be paid to the displacement resistance performance of the dangerous sections of the tunnel. The research results provide significant reference and guidance for similar projects.

Multi-scale systematization of damage and failure modes of composite cryogenic hydrogen vessels according to the Fault Tree method

Achieving a safe and lightweight design of composite liquid hydrogen (LH2) vessels without much empirical data requires advanced reliability assessment. An approach based on the Fault Tree method is proposed, to allow the systematization and modelling of functional and structural failure modes and their interactions. A hierarchical system model spanning across the length scales of the LH2 vessel down to the composite material is established. Subsequently, the failure probability of the composite material is estimated in dependence on temperature and load case using Weibull analysis. Using the accident data of US Air Carriers operating under 14 CFR 121 between 2012 and 2019, the probabilities of the load cases are derived, allowing a quantitative reliability analysis of the selected failure modes. Requirements for material and system design are derived in dependence of the maximum allowable failure probability.

Applicability of a new composite amusement ride safety device based on acoustic emission monitoring technology

Under the premise of ensuring safety, it is of great significance to realize the lightweight of the non-main load-bearing parts of amusement facilities. The purpose of this study is to study the failure process of a newly designed carbon fiber bumper by using acoustic emission technology. First of all, the design of carbon fiber anti-collision bar can effectively restrain passengers, and its weight is reduced by nearly two-thirds compared to traditional metal materials. Subsequently, the load-bearing capacity of the bumper was tested and acoustic emission monitoring was carried out. The test results show that this new type of combined structure of amusement facility has high reliability, which exceeds the safety factor of 3.5 required by the steel structure of amusement facility. In addition, Renyi entropy was used to select the best window function of short-time Fourier transform, and the frequency domain characteristics of acoustic emission signals of typical damage modes were discussed through appropriately selected windows function. A classifier based on supervised machine learning is established by combining frequency features and acoustic emission feature parameters. Furthermore, the use of classifiers helps to understand the damage behaviour of composite structures.

Damage characteristics of rock induced by unloading in hole under true triaxial boundary stresses: Experimental study

In order to study the effect of unloading of underground rock excavation on the stability of surrounding rock, the true triaxial compression (TTC) and coupled true triaxial compression and in-hole loading-unloading tests (TTC-HU) were conducted on hollow cubic rock (100mm × 100mm × 100mm). The experimental results indicate that the compressive strengths of the specimens increase as confining pressure increases in the equal biaxial stressand increase with increasing intermediate principal stresses in the unequal biaxial stress. At low confining pressure (σ < 30 MPa), the internal stress at unloading damage in the hole of hollow cubic specimen increases with the increase of the three-directional boundary stresses. At high confining pressure (σ ⩾ 30 MPa), the specimen will not be damaged during the entire unloading process in the hole. The damage mode of the specimen is dominated by tensile damage. The shape of the holes in the specimens did not significant change, and hole wall of specimen have layered destruction along the circumference in low confining pressure. In high confining pressure, the hole area of the specimen undergoes significant deformation damage, forming a V-groove along the direction of the minimum principal stress, and the wall of the hole is completely peeled off. This study can reasonably predict the actual engineering damage patterns and guide the optimization of surrounding rock support.

Effect of impact spacing on the dynamic response of UHMWPE fiber composites under two-point high velocity impacts

The impact from multiple bullets leads to more severe damage to fiber composite laminates, and the dynamic response becomes more complex. However, current research has focused on studying the ballistic limit and single impact response of materials. In this study, an experimental method to investigate the dynamic response and damage modes of fiber composite materials under multi-point asynchronous impacts is proposed. The aim is to reveal the mechanisms behind the differences in ballistic limits and energy absorption of UHMWPE (Ultra-High Molecular Weight Polyethylene) fiber composite panels at different impact distances. Through CT scanning and DIC (Digital Image Correlation) techniques, the delamination area and dynamic response of the laminates were quantitatively analyzed. The results show that the ballistic limit of the second impact is increased by 3.05 % when the impact distance is 2.5 times the diameter of the bullet. The maximum difference of energy absorption compared to the first impact was only 3.7 % at an impact spacing of 5 times the diameter of the bullet, despite the interference in the damage region. From the perspective of energy absorption, the two impacts are independent. Multiple impact tests are critical for protective materials, and the results of this study provide important insights into UHMWPE fiber laminates in terms of multi-point impact.

Compression deformation characteristics and mechanisms study of multi‐layer structures with triply periodic minimal surfaces

AbstractTriply periodic minimal surfaces (TPMS) and honeycomb structures are typical representatives of porous structures. In this paper, multi‐layer structures based on the combination of P‐surfaces and honeycomb structures are fabricated and the compression deformation characteristics are investigated based on quasi‐static compression tests and finite element simulation. The results show that the established finite element model can better simulate the deformation and damage modes of the multi‐layer structure, and the multi‐layer structure exhibits layer‐by‐layer deformation and sequential compression collapse in the deformation process. The tensile stress is crucial in the deformation and damage process of the P‐structure layer. The honeycomb structure layers show two different deformation modes: the inverted bell‐shaped “upward extrusion” and the bell‐shaped “downward extrusion.”

Study on bearing capacity and damage mode of carbon fiber composite J-type structures in oilfield completion tool connections

Carbon fiber composite structures have a broad application prospect in oilfield completion tool module connection. However, the material failure mechanism is still unclear. In this paper, the mechanical properties and failure mode of T700/7901 composite J-type structure are investigated from experimental and finite element perspectives. Firstly, the load-carrying and failure properties of the structure were analyzed through typical mechanical property experiments such as tensile, bending, and compression, and the fiber, matrix damage, and delamination damage are the main reasons for the failure of the mechanical properties of the material. Secondly, a numerical model of the progressive damage ontological relationship of the composite material was established, and the accuracy of the model was verified by combining the experimental results. Based on the above study, this paper proposes the failure mechanism and optimization of composite J-type, which provides useful guidance for the design of fiber composite structures for oilfield completion tool types in the future.

Enhancing the acoustic emission technique using fuzzy artificial bee colony-based deep learning for characterizing selective laser melted AlSi10Mg specimens

This article presents a classification of Acoustic Emission (AE) signals from AlSi10Mg specimens produced via Selective Laser Melting (SLM). Tensile tests characterized the mechanical properties of specimens printed in different orientations (X, Y, Z, 45°). Initially, a study quantified damage modes based on the stress-strain curve and cumulative AE energy. AE signals for each specimen (X, Y, 45°, Z), across deformation stages (elastic and plastic), and damage modes were analyzed using continuous wavelet transform to extract time-frequency features. A novel convolutional neural network, based on artificial bee colonies and fuzzy C-means, was developed for scalogram classification. Data augmentation with Gaussian white noise enhanced the approach. Cross-validation ensured robustness against overfitting and suboptimal local maxima. Evaluation metrics, including the confusion matrix, precision-recall curve, and F1 score, demonstrated the algorithm's high accuracy of 92.6%, precision-recall curve of 92.5%, and F1 score of 92.5% for AE signals based on printing direction (X, Y, 45°, Z). The study highlighted the potential for improving AE signal classification related to elastic and plastic deformation stages with 100% accuracy. For damage modes, the algorithm achieved a confusion matrix accuracy of 90.6%, a precision-recall curve of 90.4%, and an F1 score of 90.5%. This approach demonstrates high accuracy in classifying AE signals across different printing orientations, deformation stages, and damage modes of AlSi10Mg specimens manufactured through SLM.

Research on the influence of foaming silica gel-filled on low-velocity impact performance of M-type GFRP foldcore sandwich structure

The M-type GFRP foldcore was prepared by thermal pressing method, and was bonded with the panel to obtain the complete foldcore sandwich structure and filled the core with foaming silica gel. The influence of filling foam, impact energy and impact position on the damage mode and impact dynamic response under the low-velocity impact of GFRP M-type foldcore sandwich structure is studied through low-velocity experiment. The results show that the impact resistance of Node-impact is better than the Base-impact under low energy impact, while the Node-impact is worse than the Base-impact under high energy impact. Filling foam could effectively improve the impact properties of the foldcore sandwich plate and decrease the damage degree of the sandwich plate. In addition, filling foam could absorb about 16–26% more energy than the empty core sandwich plate.

Influence of air DBD plasma treatment on the shear and flexural strength of adhesively bonded glass fiber reinforced epoxy composite joints

In this study, air dielectric barrier discharge (DBD) plasma treatment was applied at various voltages and treatment durations to improve the bonding strength of glass fiber reinforced epoxy composites (GF/EP). In addition, single lap shear and three-point bending strengths of adhesively bonded joints were compared between untreated and surface-treated (sanding, peel ply, and plasma) samples. Surface properties of GF/EP composites were examined using contact angle, surface free energy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM). Then, mechanical tests (single lap shear and three point bending) were performed and the damage modes were determined. Surface analyses revealed that wettability and polar functional groups increased on the GF/EP surface after plasma treatment. From the mechanical test results, it was observed that the plasma treatment applied to GF/EP composites increased both single lap shear and flexural strength compared to untreated, sanding and peel ply surface treatments. After both single lap shear and 3-point bending tests, adhesive, and light fiber tear failure modes were observed.

Cryopreservation and Rapid Recovery of Differentiated Intestinal Epithelial Barrier Cells at Complex Transwell Interfaces Is Enabled by Chemically Induced Ice Nucleation.

Cell-based models, such as organ-on-chips, can replace and inform in vivo (animal) studies for drug discovery, toxicology, and biomedical science, but most cannot be banked "ready to use" as they do not survive conventional cryopreservation with DMSO alone. Here, we demonstrate how macromolecular ice nucleators enable the successful cryopreservation of epithelial intestinal models supported upon the interface of transwells, allowing recovery of function in just 7 days post-thaw directly from the freezer, compared to 21 days from conventional suspension cryopreservation. Caco-2 cells and Caco-2/HT29-MTX cocultures are cryopreserved on transwell inserts, with chemically induced ice nucleation at warmer temperatures resulting in increased cell viability but crucially retaining the complex cellular adhesion on the transwell insert interfaces, which other cryoprotectants do not. Trans-epithelial electrical resistance measurements, confocal microscopy, histology, and whole-cell proteomics demonstrated the rapid recovery of differentiated cell function, including the formation of tight junctions. Lucifer yellow permeability assays confirmed that the barrier functions of the cells were intact. This work will help solve the long-standing problem of transwell tissue barrier model storage, facilitating access to advanced predictive cellular models. This is underpinned by precise control of the nucleation temperature, addressing a crucial biophysical mode of damage.

Effect of steel fibre with different orientations on mechanical properties of 3D-printed steel-fibre reinforced concrete: Mesoscale finite element analysis

It is widely recognized that steel fibres exhibit directional distribution during the preparation of 3D-printed steel fibre reinforced concrete (SFRC). The degree of fibre orientation varies due to several factors, such as nozzle size and layer height. This variation in fibre orientation range may result in different mechanical performance exhibited by 3D-printed SFRC at hardened state. To explore the relationship between steel fibre orientation and the mechanical properties of 3D-printed SFRC at hardened state, this study firstly establishes three-dimensional mesoscale finite element models based on the distribution of fibres in 3D-printed SFRC. The steel fibre and matrix work together through a mechanism for fluid-structure interaction between models. Then, compares the simulation results with experimental data to verify the accuracy of the models. After that, different steel fibre distribution orientations were set, and parametric analysis was conducted for the compressive and tensile loading conditions to explore the effects of fibre orientation on the damage mode and strength of 3D-printed SFRC. The results indicate that 3D-printed SFRC exhibits different damage modes with varying steel fibre orientation ranges. Additionally, the strength of 3D-printed SFRC varies in steel fibre orientation range and exhibits anisotropic characteristics. This study provides a theoretical basis for improving and controlling the performance of 3D-printed SFRC in future engineering applications.

Ballistic performance and energy transfer of ultrahigh molecular weight polyethylene laminate

Soldier protection is crucial in contemporary localized conflicts, However, the impact response mechanism of UHMWPE laminate as the insert plate of ballistic helmet and bulletproof vest is still unclear. This study utilized 3D-DIC technology to analyze the impact response of UHMWPE laminates subjected to a 9 mm lead-core pistol bullet at a velocity of 334.93 m/s. The damage mode and response characteristics of the back surface were revealed; an effective numerical calculation method was established and could reveal the energy conversion process. The bullet penetrated the front face with 1.01 mm, resulting in a cross-shaped failure feature due to fiber bundle compression and aggregation. The numerical model confirmed its accuracy by comparing the height, width, and inplane strain distribution within the inplane of the bulge with experimental results. It further investigated the interaction between the bullet and the laminate, and energy transformation. The bullet's kinetic energy decreased by 80.64 %, in which the laminate absorbs 30.84 % of the bullet's energy as internal energy and 35.06 % as kinetic energy, meanwhile the bullet's internal energy increases by 11.77 %. The results show the damage mode and energy transformation of laminate, which provides theoretical support for revealing the impact response mechanism and improving the protective energy absorption efficiency.

Effect of corrugated steel angle on the damage characteristics and anti‐explosion performance of corrugated steel–concrete composite structures

SummaryA three‐dimensional refined numerical simulation model of a corrugated steel–concrete slab composite structure under contact explosion load was established by the finite element model and smoothed particle hydrodynamics(FEM‐SPH) coupling method to explore the anti‐knock properties of corrugated steel reinforced concrete slabs with different angles. The effects of corrugated steel angle on the dynamic response, damage evolution characteristics, damage mode, anti‐knock property, and propagation mechanism of the shock wave in the composite structure were investigated, and the damage prediction and anti‐knock property evaluation of the composite structure were carried out. The results show that the simulation results of the mid‐span displacement of the corrugated steel are consistent with the experimental results, and the maximum error is 2.3%, which verifies the effectiveness of the contact explosion simulation process. The mid‐span displacement, peak stress, acceleration at the center point, and energy absorption value of 90° corrugated steel are 17.9%, 70.5%, 88.6%, and 59.4% lower than those of 30° corrugated steel. The damage range of the composite structure gradually decreases with increasing angle of the corrugated steel. The failure volume of the concrete slab reinforced by corrugated steel with different angles decreases with increasing angle of the corrugated steel, and the energy absorption value of the composite structure increases with increasing of angle of the corrugated steel, mainly because the corrugated steel increases the number of reflections of the stress wave. The research results can provide a theoretical basis for the application of composite structures in the field of structural anti‐explosion protection.

Fire behavior and post-fire residual tensile strength prediction of carbon fiber/phthalonitrile composite laminates

Carbon fiber/phthalonitrile (Cf/PN) composite has a high potential for applications in the aerospace sector because of the outstanding heat and flame resistance of phthalonitrile resin. Here we aim to evaluate the fire behavior of Cf/PN laminate under localized one-sided flame heating as well as the residual tensile performance. The residual tensile strength after quasi-isothermal pyrolysis in an inert environment decreases linearly with the increase in the pyrolysis degree. The temperature response and pyrolysis behavior are analyzed through a combination of experiments and finite element simulations, and the damage mode of the laminate structure is concluded through morphological observation after flame exposure and the surface axial strain field using digital image correlation. Eventually, the residual tensile strength of laminates with different thicknesses after different times of flame exposure was effectively predicted based on the numerical simulated pyrolysis degree distribution. This research supplies fundamental test data on the mechanical properties of Cf/PN laminates and is expected to provide guidelines for the engineering application of Cf/PN composites in thermal protection/load-bearing all-in-one structures.

Effects of thermo-oxidative aging on progressive bending damages and electromechanical behaviors of carbon fiber/epoxy 3D woven composites

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens.

Preventing Staphylococci Surgical Site Infections with a Nitric Oxide-Releasing Poly(lactic acid-co-glycolic acid) Suture Material.

Of the 27 million surgeries performed in the United States each year, a reported 2.6% result in a surgical site infection (SSI), and Staphylococci species are commonly the culprit. Alternative therapies, such as nitric oxide (NO)-releasing biomaterials, are being developed to address this issue. NO is a potent antimicrobial agent with several modes of action, including oxidative and nitrosative damage, disruption of bacterial membranes, and dispersion of biofilms. For targeted antibacterial effects, NO is delivered by exogenous donor molecules, like S-nitroso-N-acetylpenicillamine (SNAP). Herein, the impregnation of SNAP into poly(lactic-co-glycolic acid) (PLGA) for SSI prevention is reported for the first time. The NO-releasing PLGA copolymer is fabricated and characterized by donor molecule loading, leaching, and the amount remaining after ethylene oxide sterilization. The swelling ratio, water uptake, static water contact angle, and tensile strength are also investigated. Furthermore, its cytocompatibility is tested against 3T3 mouse fibroblast cells, and its antimicrobial efficacy is assessed against multiple Staphylococci strains. Overall, the NO-releasing PLGA copolymer holds promise as a suture material for eradicating surgical site infections caused by Staphylococci strains. SNAP impregnation affords robust antibacterial properties while maintaining the cytocompatibility and mechanical integrity.