Failure Mechanisms Of Structures Research Articles

Non-monotonous strengthening effects of polyurea layer on polyurea-aluminum composite plate subjected to blast of charge with prefabricated fragments

In order to elucidate the failure characteristics and mechanism of polyurea-coated lightweight metal structures (taking 6063-T5 aluminum alloy plate as an example) under the combined actions of blast and high-speed fragment groups, a field test, micro analysis, numerical simulations, and theoretical analysis were conducted in this work. The results demonstrated interesting phenomena; notably, the emergence of non-monotonous strengthening effects of polyurea on composite structures was discovered. Under the examined test conditions, it was found that polyurea application on either the front or back aggravated damage of the substrate at a certain coating thickness rather than providing an enhancing protective effect. This was due to the lateral accumulation of stresses on the aluminum plate caused by the unilateral coating of polyurea, which limited the energy absorption effect. A certain polyurea coating thickness on both sides was found to be conducive to the glass transition of polyurea, which improved the protective performance of the target plate. This study could serve as a reference for the practical application of polyurea spraying technology under the combined actions resistance of metal thin-walled structures.

Seismic Fragility Assessment for a Newly Developed Buried Arch Bridge

This study aims to assess the seismic response of a newly developed buried arch bridge system. The proposed buried arch bridge system is comprised of precast concrete panels, external steel outriggers, and steel V-strips to solve the limitation encountered in the storage, transportation, and construction of traditional buried arch structures. The three-dimensional finite element analysis of this arch system is conducted under dynamic analysis emphasizing the frequency content of earthquakes. Then, the fragility curves are suggested for this arch system based on two damage states defined via incremental dynamic analysis. The results show that this proposed arch system is significantly affected under a high frequency content earthquake compared to the low and intermediate ones. Additionally, the arch system deflects the most at the mid-high position rather than at the arch crown. The deflection at the arch crown or at the mid-high position can be used for establishing the fragility curves as they both connect with the failure mechanism of the arch structure.

Experimental study on crashworthiness and failure mechanisms of aeronautical multi-fibers hybrid composite corrugated structures with Carbon, Glass, Kevlar

Crashworthiness of aeronautical composite structures can be effectively regulated and controlled by fiber hybridization design, because the structural failure modes are highly sensitive to hybrid parameters. However, the complex failure mechanism is still unclear, resulting in the inability to optimize the fiber hybridization. Hence, this study focuses on crashworthiness and failure mechanisms of aeronautical multi-fiber hybrid composite corrugated structures consisting of carbon, glass, and Kevlar fiber. The composite corrugated structures with single-fiber, double-fiber hybridization and triple-fibers hybridization are prepared by hand lay-up process. The quasi-static axial crushing tests are conducted to evaluate the crashworthiness and failure modes. The experimental results show both the crashworthiness and failure modes are very sensitive to fiber hybridizations with different fiber type and stacking sequence. Both double-fiber hybridization and triple-fibers hybridization can obtain high comprehensive properties including specific properties and cost effectiveness. However, Kevlar fibers placed in inner layers or alternately stacked with other fibers are vulnerable to the buckling-dominated failure mode that is detrimental to energy-absorption. The typical failure mechanisms of proposed hybrid composite corrugated structure are extensively revealed through the corresponding mechanism models. Overall, this study on disclosing complex failure mechanism can guide the optimization of fiber hybridization to improve crashworthiness of hybrid fiber composite corrugated structures.

Experimental and numerical investigation on crashworthiness of composite reinforced auxetic cellular tubes

This study aims to investigate the crashworthiness properties of thin-walled foam-filled Auxetic metal/composite cellular tubes under quasi-static and low-velocity impact axial loading. The specimens were fabricated using thin-walled steel tubes and Glass Fiber Reinforced Composite (GFRC) laminates. The crashworthiness characteristics including peak load, absorbed energy, specific absorbed energy, and failure mechanisms of the hybrid structures were studied and compared with individual hollow section and foam-filled Auxetic tubes. In addition, detailed FE simulations were performed using LS-DYNA software, which was verified by the experiments.

Deformation and failure mechanism of metro shield tunnel subjected to buried fault dislocation

Numerous studies have shown that tunnels are vulnerable to damage due to fault dislocation. To investigate the deformation response and structural failure mechanism of the metro shield tunnel subjected to faulting, model tests with a geometric similarity ratio of 1:25 were carried out to analyze the influence of fault dislocation on the tunnel. The deformation of segmental lining and circumferential joints, earth pressure, and strain evolution were investigated. Combined with numerical simulations, the deformation and failure pattern of the shield tunnel after normal and reverse faulting were revealed. The failure criterion of segmental lining was discussed thoroughly. The results show that after faulting, the differential settlement, convergence deformation, strain response, and the soil pressure near the interface between the shield tunnel and the path line of fault increase remarkably. A horizontal duck egg-shaped deformation profile of segments is presented. The longitudinal cracks are distributed inside the tunnel vault and outside the tunnel haunch. The circumferential joint of shield tunnel is damaged severely under normal faulting, and the opening between segment rings exceeds the deformation limit of joint waterproofing. While tensile damage of the circumferential joint under reverse faulting is less evident, and the opening between segment rings is slight. The numerical simulation results have consistency with the consequence of the experiments. In addition, no circumferential crushing or oblique shear failure occurred in the model segment, and the deformation and tensile fracture damage of the circumferential joint should be deemed as the failure criterion of shield tunnels under faulting. Finally, countermeasures and suggestions are proposed for the structural design of metro shield tunnels overcrossing buried faults.

Structural Failures of Adobe Buildings during the February 2023 Kahramanmaraş (Türkiye) Earthquakes

Türkiye experienced great destruction during the Kahramanmaraş earthquake couple which occurred as Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) on 6 February 2023. The weak structural characteristics and the magnitude of the earthquakes caused more than 50,000 casualties. Significant damage occurred in both urban and rural building stock in 11 different provinces that were primarily affected by the earthquakes. The dominant building stock is masonry structures in the rural areas of the earthquake region. Structural damages at various levels have occurred in adobe masonry structures built using local labours and resources without any engineering service. The main purpose of this study is to examine the failure and collapse mechanisms of adobe structures after Kahramanmaraş earthquakes in detail. First of all, information about both earthquakes was given. The earthquake intensity for all provinces was obtained by using the peak ground acceleration-intensity relation suggested for Türkiye, taking into account the measured PGAs in earthquakes. The observed structural damages were evaluated in terms of earthquake and civil engineering in adobe structures. Damage classification was conducted using European Macro-Seismic Scale (EMS-98) for a total of 100 adobe buildings. Of these structures, 25% were destroyed, 49% were heavily damaged, 15% were damaged moderately, and 11% were damaged slightly. In addition, the rules regarding adobe structures were compared considering the last two earthquake design codes used in Türkiye. In the study, suggestions were also presented to prevent structural damage in the adobe buildings in the earthquake region. Low strength of adobe material, usage of heavy earthen roofs, failure to comply with earthquake-resistant building design principles, and insufficient support of load-bearing walls are the main causes of damage.

STUDY ON EARTHQUAKE DESTRUCTION MODE OF THE LARGEST CANAL CROSSING HIGHWAY BRIDGE BASED ON IEM BOUNDARY IN SOUTH-TO-NORTH WATER DIVERSION

To study the dynamic failure mechanism and damage development law of highway bridge structure under the boundary effect in the process of seismic dynamic duration, the Wenchang Highway Bridge with the largest canal crossing in the South-to-North Water Diversion is taken as an example for seismic design analysis. Based on the finite element and infinite element coupling theory, the infinite element method boundary is introduced, the concrete damage plasticity is introduced, and the half-space free field model is established to study the energy dispersion phenomenon of waves in the boundary and the absorption effect of the infinite element method boundary on wave energy is verified. Under different peak acceleration intensities, the seismic response analysis of the bridge structure was carried out. The results show that: Under the action of selected artificial waves, the damage location of the bridge mainly concentrated in the junction of the box girder supported by the pier, the bottom of the pier and the junction of the pier and beam. The damage tends to develop downward near the bottom of the box girder. The damage at both ends of the beam extends from both ends to the middle. And the bottom and top of the pier have penetrating damage. These are weak points in seismic design. At a horizontal peak acceleration of 0.6g, in addition to damage to the pier column, damage also occurred to the bottom of the box girder. Therefore, when the horizontal peak acceleration of the seismic wave is greater than 0.6g, the failure of the bottom of the box girder is paid attention to. Moreover, the IEM boundary has a good control effect on the far-field energy dissipation of the wave, which is simpler and more efficient than the viscous–spring boundary.

Bending Performance and Crashworthiness Characteristics of Sandwich Beams with New Auxetic Core

Structures with enhanced mechanical properties and crashworthiness are competing materials in the transport industry to reduce structural weight, and auxetic materials are the ideal choice. Auxetic metamaterials are the class of cellular structures designed to possess negative Poisson's ratio. The current study evaluates newly developed re‐entrant diamond auxetic metamaterial's in‐plane and out‐of‐plane three‐point bending performance. A series of experimental and numerical studies are performed to assess the quasistatic performance and crashworthiness characteristics of 3D‐printed re‐entrant diamond auxetic core and sandwich panels. The results are compared with regular re‐entrant panels of the same unit cell size. The deformation and failure mechanism of both auxetic structures, core and sandwich, are discussed. Real‐time displacement contours on the specimen surface are visualized using advanced image processing and finite‐element methods. The new re‐entrant diamond auxetic members outperformed energy absorption characteristics in in‐plane and out‐plane directions. Compared to the counterpart, the new metamaterial has improved 88.33% and 29.24% in‐plane energy absorption as a core and sandwich, respectively. 13.51% and 13.35% increments in energy absorption as a core and sandwich are observed for re‐entrant diamond structures compared to the regular re‐entrant system in the out‐of‐plane direction.

Structural characteristics, oxidation performance and failure mechanism of thermal barrier coatings fabricated by atmospheric plasma spraying and detonation gun spraying

In recent years, thermal barrier coatings (TBCs) are widely applied to the surface of gas-turbine engines to prolong the service life of high temperature components. The increase in raw material requirements and costs has led to the search for an alternative, cheaper ceramic based material to yttria stabilized zirconia (YSZ), which is the traditional TBC top coating material. In this study, CoNiCrAlY metallic bond coating powders were deposited on Ni-based superalloy substrates by the detonation gun (D-gun) process. Commercial YSZ and blast furnace slag (industrial waste) powders were deposited on the bond coating by atmospheric plasma spraying (APS) technique. TBCs were subjected to isothermal oxidation tests for 8, 24, 50, and 75 h at 800 °C. The microstructural properties of the TBCs were evaluated comparatively using advanced characterization techniques before and after oxidation tests. It has been observed that the coatings produced using BFS material have a potential to be used in different types of industries as a low-cost and environmental solution against high temperature oxidation conditions.

Applications of bond-based cohesive peridynamics method (CPDM) to simulate inelastic fracture of stiffened plates in ship hull structures

In this work, we utilize a non-local bond-based cohesive peridynamics method (CPDM) that is recently developed in Han et al. (2022) to model and simulate crack growth and crack propagation in stiffened plates, and to predict inelastic fracture processes in extensively-used stiffened plates in ship hull structures.The bond-based cohesive peridynamics method has both normal and tangential components in the bond force density, which allow for capturing of inelastic fracture processes under large deformation, and it is capable of the description of complex nonlinear material constitutive behaviors.By doing so, we have systematically simulated the fracture of stiffened plates with different types of stiffeners, such as rectangular, I-shaped, and L-shaped. Moreover, we also studied the strength effects of different sizes, layouts, and shapes of stiffeners on the fracture of plates. In specific, we calculated the structure stress intensity factors for various stiffened plate structures and study the crack arrest effect for various types of stiffeners on the hull structures. The numerical results demonstrate that bond-based cohesive peridynamics provides an accurate and reliable modeling and simulation tool for studying the structural failure mechanism of ship hull structures and predicting crack growth in stiffened plates.

Experimental study on the mechanical properties of three‐dimensional braided composite circular tubes with preembedded licker‐in

AbstractThis study investigates the tensile and compression properties of three‐dimensional five‐direction (3D5D) braided composite circular tubes with preembedded titanium alloy licker‐ins. The influence of the braided angle, braided thickness, and braided configuration on the bearing capacity is analyzed, and the microdamage morphology and failure mechanism of the tube structure are examined using scanning electron microscopy. Results show that the 3D5D braided tube has a larger tensile failure load than the 3D full five‐direction braided tube of the same outer diameter. In circular tubes of the same braided configuration and outer diameter, the compression failure load increases with the wall thickness, and the C‐ø30t3 circular tube achieves the maximum compression failure load. The damage morphology is characterized by the pulling‐off failure of the licker‐in joint. The T‐ø30t2.5 and T‐ø25t3 circular tubes achieve a large failure load, with an average tensile load of over 120 kN. The failure morphology is characterized by the cracking of the fiber at the end of the tube after the licker‐in joint has been pulled off. The average tensile failure load of the T‐ø30t3 circular tubes is over 105 kN, and the failure morphology reveals a broken licker‐in joint, indicating design deficiencies that require further optimization. The findings of this paper can provide an important scientific basis for the lightweight and high‐strength connection design for 3D braided composites in near‐space aerostats and their flight applications.

Ballistic performance of additive manufacturing 316l stainless steel projectiles based on topology optimization method

Material and structure made by additive manufacturing (AM) have received much attention lately due to their flexibility and ability to customize complex structures. This study first implements multiple objective topology optimization simulations based on a projectile perforation model, and a new topologic projectile is obtained. Then two types of 316L stainless steel projectiles (the solid and the topology) are printed in a selective laser melt (SLM) machine to evaluate the penetration performance of the projectiles by the ballistic test. The experiment results show that the dimensionless specific kinetic energy value of topologic projectiles is higher than that of solid projectiles, indicating the better penetration ability of the topologic projectiles. Finally, microscopic studies (scanning electron microscope and X-ray micro-CT) are performed on the remaining projectiles to investigate the failure mechanism of the internal structure of the topologic projectiles. An explicit dynamics simulation was also performed, and the failure locations of the residual topologic projectiles were in good agreement with the experimental results, which can better guide the design of new projectiles combining AM and topology optimization in the future.

Improved biomechanical behavior of 316L graded scaffolds for bone tissue regeneration produced by laser powder bed fusion

Graded lattice scaffolds based on rhombic dodecahedral (RD) elementary unit cell geometry were manufactured in 316L stainless steel (SS) by laser powder bed fusion (LPBF). Two different strategies based on varying strut thickness layer-by-layer in the building direction were adopted to obtain the graded scaffolds: a) decreasing strut size from core to edge to produce the dense-in (DI) structure and b) increasing strut size in the same direction to produce the dense-out (DO) structure. Both graded structures (DI and DO) were constructed with specular symmetry with respect to the central horizontal axis. Structural, mechanical, and biological characterizations were carried out to evaluate feasibility of designing appropriate biomechanical performances of graded scaffolds in the perspective of bone tissue regeneration. Results showed that mechanical behavior is governed by graded geometry, while printing parameters influence structural properties of the material such as density, textures, and crystallographic phases. The predominant failure mechanism in graded structures initiates in correspondence of thinner struts, due to high stress concentrations on strut junctions. Biological tests evidenced better proliferation of cells in the DO graded scaffold, which in turn exhibits mechanical properties close to cortical bone. The combined control of grading strategy, printing parameters and elementary unit cell geometry can enable implementing scaffolds with improved biomechanical performances for bone tissue regeneration.

Seismic failure modes of masonry structures exposed to Kahramanmaraş earthquakes (Mw 7.7 and 7.6) on February 6, 2023

In this study, the failure modes of masonry structures after the earthquakes (Mw 7.7 and 7.6) occurred in Kahramanmaraş on February 6, 2023 were investigated by fieldwork. Within the scope of the study, information of the building stock in Türkiye and the Middle East countries was given, and a literature regarding the major failure modes in masonry structures was mentioned. The characteristics of the ground acceleration and earthquake parameters measured during the earthquake were presented. Damage distributions in historic masonry structures and masonry dwellings were examined. In addition to the out-of-plane behavior which is the most common failure mechanism in masonry structures, the corner failure mechanism has been also observed in many masonry buildings. It has been determined that the corner failure mechanism is triggered by the combination of the in-plane and out-of-plane failure behaviors. In this manner, the observed damages were classified as in-plane, out-of-plane, and corner failures. It has been determined that damaged masonry structures are mostly out of use with out-of-plane and corner failure mechanisms. These two failure mechanisms were directly related to inadequate wall-roof and wall-floor connections, insufficient axial load, low material strength, poor workmanship, and the lack of engineering service. In-plane failure mechanisms are triggered by irregular door and window openings exceeding the limits given in the regulations. In addition, it has been revealed that many masonry buildings do not have adequate vertical and horizontal lintel band to increase the lateral seismic performance of the walls. In the last part of the study, the advantages and disadvantages of the strengthening methods that can be used in masonry structures with light and moderate damage were examined, and some suggestions were made.

Tensile strength and failure behavior of rock-mortar interfaces: Direct and indirect measurements

The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures, such as concrete gravity dams. Despite the critical importance of the failure mechanism and tensile strength of rock-concrete interfaces, understanding of these factors remains very limited. This study investigated the tensile strength and fracturing processes at rock-mortar interfaces subjected to direct and indirect tensile loadings. Digital image correlation (DIC) and acoustic emission (AE) techniques were used to monitor the failure mechanisms of specimens subjected to direct tension and indirect loading (Brazilian tests). The results indicated that the direct tensile strength of the rock-mortar specimens was lower than their indirect tensile strength, with a direct/indirect tensile strength ratio of 65%. DIC strain field data and moment tensor inversions (MTI) of AE events indicated that a significant number of shear microcracks occurred in the specimens subjected to the Brazilian test. The presence of these shear microcracks, which require more energy to break, resulted in a higher tensile strength during the Brazilian tests. In contrast, microcracks were predominantly tensile in specimens subjected to direct tension, leading to a lower tensile strength. Spatiotemporal monitoring of the cracking processes in the rock-mortar interfaces revealed that they show AE precursors before failure under the Brazilian test, whereas they show a minimal number of AE events before failure under direct tension. Due to different microcracking mechanisms, specimens tested under Brazilian tests showed lower roughness with flatter fracture surfaces than those tested under direct tension with jagged and rough fracture surfaces. The results of this study shed light on better understanding the micromechanics of damage in the rock-concrete interfaces for a safer design of engineering structures.

Limit state design of resilient earthquake-resisting systems

Sustainable seismic design (SSD) is the first step towards next-generation earthquake engineering. SSD of mixed multiple seismic systems (MMSSs), in which more than one earthquake-resisting structure is used, is a challenging structural engineering issue. Seismic sustainability implies survivability during and after an earthquake, preceded by post-earthquake realignment and repairs (PERR). Purpose-specific MMSSs are ideally suited for SSD. However, contemporary codes address neither the sequences nor the failure mechanisms of the earthquake-resisting structures of MMSSs. The difference between conventional design and SSD is their approach to expected behaviour during and after an earthquake. Earthquakes are natural and dynamic occurrences, whereas PERR is a manual and static process. SSD does not favour unreal detailing or oversimplifying assumptions; it is a multi-faceted effort that involves realistic structural analysis and planned manual operations. In this context, design implies operability with a view to PERR and requires a change from damageability assessment and performance-based seismic design to performance control and reparability-based design, including the development of new analytic tools and purpose-specific details. This article presents graphical solutions and theoretical principles to help achieve practical SSD for MMSSs. These new techniques may be used for practical reliability, economy and environmental protection.

Mechanical responses of buoyant bio-inspired foamed concrete structures

This work proposes a new type of lightweight cellular foamed concrete (FC) inspired by natural cellular structures with controllable mechanical properties for different prefabricated engineering applications. The 3D printed formworks are inspired by the lattice structure and triply periodic minimal surface (TPMS) architectures, including gyroid and primitive prototypes. These 3D printed sacrificial thermoplastic Polylactic Acid (PLA) formworks were then infiltrated with two types of foamed concrete with different densities of 600 kg/m3 and 800 kg/m3 and subjected to uniaxial compressive loadings. Furthermore, the X-ray computed tomography (CT) scan was conducted on the prefabricated structures to further observe the PLA-foamed concrete contact region and to investigate the air void characteristics. Numerical simulation was employed for further investigation on the structural performance and failure mechanism of three bio-inspired structures (TPMS-Primitive, -Gyroid, and strut-based lattice). By both numerical and experimental investigations, the gyroid cellular structure yields the highest compressive capacity, followed by the primitive and lattice structures, respectively. Furthermore, based on the X-ray micro-CT scan, the bio-inspired architecture of the moulds showed a significant effect on the size and distribution of air voids, which highly influenced the compressive strength of the infiltrated foamed concrete.

Mechanical properties and failure mechanisms of polyamide 12 gradient scaffolds developed with selective laser sintering

Developing a functional gradient scaffold compatible with the fantastic biological and mechanical properties of natural bone tissue is imperative in bone tissue engineering. In this work, the stretch-dominated (cubical and circular) and bending-dominant (diamond and gyroid) pore styles were employed to design custom-graded scaffolds based on the curve interference method and then were fabricated by selective laser sintering (SLS) using polyamide 12 (PA12) powder. Subsequently, the mechanical behavior, failure mechanism, and energy absorption performance of porous structures were investigated via compression experiments and finite element (FE) simulation. The results indicated that the stretch-dominated radial gradient structures entire exhibited transverse shear failure and the bending-dominant radial gradient structures whole exhibited progressive destruction, while all of the axial gradient scaffolds suffered a predictable layer-by-layer fracture. Among them, the bending-dominated radial gradient structure of gyroid had been proven to sustain stronger deformability and energy absorption capacity. Meanwhile, the FE method powerfully predicted the mechanical behavior of the scaffold, and this research thereby possessed significant implications for the development of bone tissue engineering.

Sustainability-driven atomistic model for exploring the mechanical properties of low carbon limestone calcined clay cement (LC3)

Limestone Calcined Clay Cement (LC3) is identified as a promising alternative to cement blends, and it has become an effective way to alleviate the environmental burdens in the cement industry due to its sustainable nature. In this work, we developed the first molecular model to describe the optimized properties of LC3 blend considering its natural sustainability. The proposed model entails the atomistic structures of Calcium-aluminate-silicate-hydrate (C-A-S-H) in LC3, identifying its mechanical properties, tensile deformation behaviors and failure mechanisms. We revealed that the natural atomistic origins contributing to the superior mechanical properties of C-A-S-H in LC3 compared to that in plain cement are: (1) highly polymerized aluminate-silica chain in C-A-S-H enhances its mean chain length and reduces its porosity; and (2) highly activated aluminate monomer strengthens the cross-linked network in C-A-S-H through a series of pozzolanic reactions. Furthermore, we elucidated the failure mechanisms including aluminate-silica chain breakage, nanopore expansion and microcrack evolution of C-A-S-H under tensile loading. Our findings provide atomic insights to uncover the nanoscale structures of C-A-S-H in sustainable LC3, portraying new understandings of their complicated molecular interactions and structural-failure mechanisms and paving ways for the development of sustainable cementitious composites for construction industry with lower environmental impacts.

Prediction of the seismic behavior and backfilling scheme optimization of immersed tunnel based on the ruyifang project

The backfill soil is the first line of defense that ensures immersed tunnel's safety and stability, but its seismic performance has not been investigated in previous studies. This study employs the Ruyifang tunnel as its research object to determine the most dangerous cross-section. It establishes a two-dimensional soil-structure interaction system for complex sites to evaluate immersed tunnels' safety during earthquakes, clarify the structural failure mechanism, and optimize the backfilling scheme. In addition, this study investigates the tunnel element's response, damage, and stress under static and dynamic loads and obtains the impact of backfilling materials by considering plastic damage in structures, soil viscoelastic properties, and various backfilling schemes. The results showed that the tunnel section's stress has prominently distributed characteristics. Moreover, the structure exhibits tensile failure during ground motions, and the bottom of the side wall is the critical area. The inertial force is the primary factor affecting the seismic capacity at the overburden layer and flanks, while stiffness plays a vital role at the cushion. These dynamic properties and related backfilling technology can provide technical support for the anti-seismic design of immersed tunnels.