Bending Failure Mechanism Research Articles

Effects of high-intensity microwave (HIMW) treatment on mechanical properties and bending failure mechanisms of radiata pine (Pinus radiata D. Don)

Effects of high-intensity microwave (HIMW) treatment on mechanical properties and bending failure mechanisms of radiata pine (Pinus radiata D. Don)

Experimental analysis of 3D printed continuous carbon/glass hybrid fiber reinforced PLA composites: Revealing synergistic mechanical properties and failure mechanisms

AbstractThis study investigates the mechanical properties of continuous carbon/glass hybrid fiber‐reinforced polylactic acid (PLA) composites (HFRC) produced through the three dimensions (3D) printing process, comparing them with single carbon fiber‐reinforced PLA composites (CFRC). Initially, composite prepreg filaments are prepared using an impregnation device, followed by fabrication using a 3D printer. The mechanical performance results reveal a 13% increase in tensile strength for HFRC compared with CFRC. Due to differing elongation rates of carbon and glass fibers, HFRC exhibits two strength peaks, while CFRC demonstrates a 37% higher bending strength than HFRC. Scanning electron microscope images indicate that the tensile failure mechanism involves fiber brittle fracture and fiber‐matrix interface debonding, while the bending failure mechanism includes fiber pullout, fiber debonding, fiber cluster buckling, and interlayer interface failure.Highlights To realize the moldless rapid manufacturing of continuous hybrid fiber‐reinforced PLA composites. The stress–strain curves of single fiber‐reinforced composites and hybrid fiber‐reinforced composites are obviously different. Elucidating the effect of single fiber/hybrid fiber in composites on mechanical properties and failure mechanism according to micro‐morphology.

Flexural behaviour of one-part fibre-reinforced geopolymer beams

This research focuses on the structural application of one-part fibre-reinforced geopolymer composite (OP-FRGC), a pioneering low-carbon, high-performance construction material. While extensive studies have been conducted on the basic mechanical properties and mix proportions of OP-FRGC, structural applications remain underexplored. This investigation of the flexural performance of steel-reinforced OP-FRGC beams employed four-point bending tests and digital image correlation (DIC) to elucidate bending failure mechanisms. The results were then compared with those of conventional steel-reinforced concrete (RC) beams. Findings indicate that the integration of fibres in OP-FRGC effectively distributes cracks and enhances flexural toughness. Additionally, the research evaluates the predictive accuracy of existing structural codes from China, the United States, and Europe for steel-reinforced OP-FRGC beams. A comparative analysis of the carbon emissions from these structural systems underscores the environmental advantages of steel-reinforced OP-FRGC beams, highlighting their potential to reduce the carbon footprint in the construction sector.

Bending resistance mechanism of prestressed ultra-high performance concrete - reinforced concrete beam based on a full-scale experiment

Ultra-High Performance Concrete (UHPC) is a new type of engineering material with high compressive strength, high tensile strength, and high fracture toughness. Its bending failure mechanism is different from that of traditional concrete beams, which requires a new computational model to describe the bending failure phenomena of the prestressed ultra-high performance concrete - reinforced concrete (UHPC-RC) beam without web reinforcement. Therefore, this paper, through full-scale tests on a 30m prestressed UHPC-RC beam without web reinforcement, captures unique bending failure phenomena, including initial cracking, development of local cracks, and rupture of prestressed steel strands. Considering the tension-compression constitutive relationship of UHPC material, an innovative computational model for bending bearing capacity is proposed. Based on this model, a study on the minimum reinforcement ratio of full prestressed-ordinary steel bars is conducted. The results show that in the bending failure of the prestressed UHPC-RC beam without web reinforcement, excessive tensile strain of steel strands will occur at the local crack location. At this time, the structure does not satisfy the assumption of plane sections, and the introduction of the calculation model of the limit state of external prestressed tendons can effectively match this model, which is highly consistent with the experimental results. The minimum reinforcement ratio of full prestressed-ordinary steel bars is revised to the auxiliary reinforcement ratio of full prestressed-ordinary steel bars, quantifying the minimum reinforcement requirements of ordinary steel bars. The research results of this paper can provide reference for the next step of theoretical research.

Experimental investigation on failure mechanisms of hybrid steel/GFRP hat‐shaped beams under bending loading

AbstractThe bending failure mechanism and energy absorption characteristics of hybrid metal/composite structures are the keys to the side collision safety of automobiles. The purpose of this paper is to investigate the bending behavior and failure mechanism of hybrid Steel/GFRP hat‐shaped beams under three‐point bending. Firstly, both quasi‐static and dynamic three‐point bending tests were conducted on Steel, GFRP and hybrid Steel/GFRP hat‐shaped beams. Then, the effect of layups and loading speeds on the bending failure behaviors of GFRP hat‐shaped beams were investigated, and the five stages of the bending process of GFRP hat‐shaped beams were exposed. Finally, the failure mechanism of hybrid Steel/GFRP hat‐shaped beams under both quasi‐static and dynamic three‐point bending were investigated. It is found that the failure mechanism is related to the interaction effect between the Steel and GFRP parts in the hybrid Steel/GFRP hat‐shaped beam. In the bending failure process, the crack propagation in GFRP parts is delayed by the plastic deformation of the connected Steel parts, which improves the energy absorption and load carrying capacities of the hybrid Steel/GFRP hat‐shaped beam, and this improvement in the whole bending process is quantitatively exposed in this work. Besides, it is found that with the same impact energy, the load carrying capacity of the hybrid Steel/GFRP hat‐shaped beam can be increased by the loading roll diameter increasing.Highlights A bending process with five stages of GFRP hat‐shaped beams is exposed. The loading speed increases impact loads due to the strain rate strengthening. The interaction between Steel and GFRP improves the load carrying capacity. The load carrying improvement is due to crack propagation delay in GFRP parts. The greater loading roll diameter increases the load carrying capacity.

Effects of fiber orientations on fracture mechanisms in rotary ultrasonic drilling of carbon fiber reinforced plastic laminates

The fracture mechanisms of the carbon fibers seriously depend on fiber orientations which significantly influence the surface quality of carbon fiber reinforced plastics (CFRPs). Rotary ultrasonic drilling (RUD), possessing some excellent characteristics including the superior sidewall quality and high cylindricity error, offers a possibility for the efficient drilling of the CFRP components. In contrast, the effects of fiber orientations on fiber fracture mechanisms are still not fully recognized in RUD of CFRP composites. Incorporated with kinematic characteristics of the abrasive, a novel theoretical model was developed to quantitatively describe the effective orientation of the fiber. Afterwards, the drilling experiments with and without ultrasonic were conducted under the same parameters. The surface topographies of the hole sidewalls at various orientations were comparatively characterized to explore the fiber fracture mechanisms. Subsequently, the influences of these mechanisms and the drilling parameters the surface qualities were also investigated. Moreover, the bending failure mechanisms of the carbon fibers were explored through theoretical analysis. As a result, another fiber fracture mechanism, bending failure, was identified with the smooth fracture and micro-fragmentation topographies at upwind and leeward parts of the fiber cross-section, respectively. Ultrasonic superimposition by means of the immense inertia force of the abrasive promoted the micro-fracture of the carbon fiber. The weaker sustainment from the back-up materials brought about the serious bending failure of fiber oriented at 135°, while the axial load component aggravated the tensile fracture of the carbon fiber with the effective orientation of 45°. The critical moment of the fiber bending failure was also established, by incorporating the beam theory and linear elastic fracture mechanics. The fundamental investigation provided a favorable foundation for further optimizing the parameters to improve the drilling quality and efficiency in formal RUD of CFRP composites.

丸竹稈の曲げ破壊メカニズムおよび曲げ強度に関する基礎的考察

The bending failure of full-culm bamboo is usually preceded by bending failure perpendicular to the fibers of the bamboo culm walls. Therefore, it is important to evaluate the stress perpendicular to the fiber that accompanies the bending of the bamboo culm. Brazier effect is considered one of the factors that cause this stress. In this paper, we discuss the bending failure mechanism and bending strength of round bamboo culms with formulation of the Brazier effect theory, numerical analysis, and experiments.

Bending Failure Behavior of the Glass Fiber Reinforced Composite I-Beams Formed by a Novel Bending Pultrusion Processing Technique

Abstract The glass fiber reinforced resin matrix composite I-beams were designed and formed via a type of novel bending pultrusion processing technique, and the three-point bending tests were carried out to analyze the mechanical bending performances. The obtained results show that the main failure mode of the composite I-beam under the bending load is the upper structure (top flange) cracks along the length direction of the fibers, and the cracks simultaneously propagate downwards in the vertical direction. The bifurcated cracks can be found at the junction area between the top flange and web. In addition, the main bending failure mechanism of the composite I-beam includes the matrix cracking, propagation of cracks, and final fracture failure. In particular, noting that when the crack reaches the I-shaped neck position, the lateral bifurcation occurs, and the resulting secondary cracks further extend in two directions, which leads to the serious damage between the top flange and web, and the ultimate fracture failure occurs.

Bending failure mechanism of bamboo scrimber

Bamboo scrimber (BS) is becoming one of the most popular engineering bamboo composites because of its excellent physical and mechanical properties. In this study, four-point bending tests in conjunction with in-situ test methods were used to investigate the bending failure mechanism of BS, with nature bamboo (NB) as the reference comparison object. Both the macroscopic and microscopic bending properties were analyzed. Results indicated that the macroscopic load–displacement curves and micro failure morphology of BS showed a typical brittle failure, which was caused by the combined effect of tensile, shear and compressive stress. The elastic modulus of BS was significantly increased due to the increased concentration of sclerenchymatous cells per unit volume. The brittle failure mechanism of BS was shown to be strongly correlated to the compression of main energy absorption tissues contained in the cavities of vessels and parenchyma cells, the composite effect of brittle PF resin filling in the cavities, covering on the parenchyma cell wall and forming glue nails, and the decomposition of hemicellulose. This study was beneficial for the reasonable design and safe application of bamboo scrimber in practical engineering.

Evaluation of moisture diffusion characteristics and the effect of moisture treatment on flexural properties of expanded perlite-based building material

The expanded perlite-based building material for drywall application consisting of sodium silicate solution as a binder was manufactured by varying the degree of compaction and sodium silicate content to investigate moisture diffusion behavior and the effect of moisture treatment on flexural properties of the composites. Moisture treatment was conducted on specimens in a climatic chamber at a temperature of 37°C and a relative humidity of 90% until saturation. Results show that moisture absorption decreased with increasing compaction ratio for a constant sodium silicate content in binder and increased with increasing sodium silicate content in binder for a constant compaction ratio. A range of volume fractions of solid sodium silicate in the foam is identified, in which the fully Fickian diffusion gradually transformed to non-Fickian diffusion as sodium silicate content in foam increased. The concentration-dependent diffusion method was found to be suitable to explain this behavior. The moisture diffusion below this transition range showed an entirely Fickian diffusion and changed to concentration-dependent diffusion above the range. As a result of moisture treatment, the flexural strength of medium density foams was decreased but the lowest- and highest-density foams were not affected while the flexural modulus was increased only for the highest density foam and no significant effects were seen in other cases. The bending failure mechanism of the composite was not affected by the moisture treatment.

Damage evolution behavior of cold plasma treated glass fiber/vinyl ester resin composites under bending load by acoustic emission

This study reveals the preparation and mechanical characterization of cold plasma treated glass fiber/vinyl ester resin composites. The surface characteristics and bending failure mechanism of composites treated by oxygen, argon and nitrogen glow discharge plasma were studied by acoustic emission. The results showed that the bending resistance of argon plasma treated glass fiber reinforced composites exhibited highest. The composite treated by oxygen plasma produced AE signals with a frequency of more than 300 kHz, indicating that the fiber was damaged and the material was brittle, which reduced the strength and plasticity of the material. The bending stress in warp direction was greater than that in weft direction. The bending resistance of the cold plasma treated glass fiber/vinyl ester resin composites was the highest under the conditions of power 150W, flow rate 10sccm and time 120s.

Failure mechanism of unequal parameters metal bellows under repeated bending process

The metal bellows used for flexible connection of oxygen lance in metallurgical converter compensate the displacement of pipeline by its bending deformation. Due to the waveform structure, the adjacent waves at the fixed end of the metal bellows are squeezed together, leading to premature fracture. In order to explore the influence of waveform structure parameters on the failure mechanism of the metal bellows, a U-shaped metal bellows with different waveform structure parameters was designed in this paper. The ultimate repeated bending process of the metal bellows was numerically simulated by ABAQUS finite element software. The influence law of waveform structure parameters on equivalent stress, equivalent strain and ultimate bending angular displacement of the metal bellows were obtained. Then, the repeated bending fatigue life of the bellows was tested on the fatigue testing machine, and the influence law of the waveform structure parameters on the fatigue life of the bellows under ultimate bending angular displacement amplitudes was obtained. The experimental results verify the accuracy of the finite element simulation. Finally, X-ray diffraction peaks confirmed the proved that the plasticity accumulation at the wave trough of the equal parameters metal bellows (EPMB) is large, so the hardness value is large. The micro morphology of the fracture and the surrounding area was analyzed by scanning electron microscope (SEM), and the crack propagation and the ultimate repeated bending failure mechanism of the bellows with different waveform structures was revealed. The initial cracks appear in the inner and outer surfaces of the wave trough, distribute along the circumferential direction, and propagate from the inner and outer surfaces to the central layer. Among them, the fracture morphology of the EPMB is mainly composed of fatigue fracture and plastic fracture. However, the fracture morphology of the unequal parameters metal bellows (Un-EPMB) is dominated by fatigue fracture. The results show that the fatigue life and bending fracture resistance of metal bellows can be improved by designing waveform structure with unequal parameters.

Theoretical prediction model and failure mechanism map of human skull porous structures with quasi-static bending performance

A theoretical model has been developed to predict the bending properties and failure mechanism of the human skull. The structure of the skull bone, which is naturally a porous material, was obtained via non-destructive 3D micro-computed tomography. By considering the combined influence of curvature and porosity of the skull, the mid-span deflection of the skull bone loaded in three-point bending was calculated using theoretical prediction. The cranial bending peak load corresponding to several possible failure modes was also analyzed, and the relevant failure mechanism map was generated. The models also showed that the curvature is a critical consideration for accurate precisions to be achieved. To verify the reliability of the theoretical results, as well as to gain a good understanding of the intrinsic connections between internal geometric features and mechanical properties of the cranium, 3D finite element (FE) models, based on posteriorly reconstructed by 2D cranial scanning images, were developed. The bending properties of various reconstructed sections were studied in detail using the FE simulation models, leading to an understanding of the bending failure mechanism and crack propagation path. The numerical results of deflection and peak loads agree well with the theoretical results. In addition, the failure modes of the numerical models have been verified using published experimental results. This work has overall demonstrated that the theoretical and numerical models would provide a reliable basis for predicting cranial bending performance.

Effect of pile arrangement on the bending performance of an existing bridge footing under lateral seismic loading

In this paper, to further understand the bending failure mechanism of a bridge footing subjected to lateral seismic loading, the effect of pile arrangement on the bending performance of a footing is mainly investigated by parametric analysis. The pile location can considerably affect the bending failure pattern of the footing by constraining the extent of yielding of footing top bars. The piles placed at the center of the sides parallel to the loading direction can constrain the extent of yielding of the top bars in the loading direction. Similarly, the piles at the center of the sides perpendicular to the loading direction can constrain the extent of yielding of the top bars in the other direction. The center pile can constrain the extent of yielding of the top bars in two directions. Additionally, based on the analytical results of the parametric analysis, the application condition of the current beam theory-based design method expected to accurately evaluate the footing bending capacity is discussed from the aspect of pile spacing.

Effect of curing degree on mechanical and thermal properties of 2.5D quartz fiber reinforced boron phenolic composites

Abstract2.5D quartz fiber reinforced boron phenolic composites with different curing degrees were prepared by different curing temperatures and curing times. The effects of curing degree on the flexural strength and thermal properties of the composites were investigated by mechanical properties test, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The results show that the flexural strength increases to the increase in the degree of cure, but the rate of increase is non-linear. When the degree of cure is higher than 90%, the flexural strength of the composite is more than 300 MPa and the bending failure mechanism of the composite is analyzed by SEM. The TG test showed that the degree of cure had little effect on the residual weight of the composite at 1000°C, but had a greater effect on the temperature of the previous weight loss.

Bending failure mechanism and strengthening of concrete-filled steel tubular support

Concrete-filled steel tubular (CFST) support is an innovative and effective support technology, which has been broadly applied in underground roadways. However, failure is still possible, and the primary failure locations are commonly the vault and the springline. In order to reveal the failure mechanism and provide an effective solution, the inner forces of a circular CFST support were investigated analytically. To improve the flexural performance, firstly, the flexural behavior of CFST beams strengthened by welded steel at soffit was investigated experimentally. A total of 6 beams were tested under a four-point bending load, and the investigated parameter was welded steel diameter. The corresponding nonlinear three-dimensional finite element model was established in the ABAQUS software and was validated using the experimental results. Then, the effect of welded range and welded location on the support bearing performance was investigated numerically. Finally, the proposed method was validated by an application example. Results show that CFST support bearing performance is greatly improved when the lateral pressure coefficient is equal to 1.0, because there is no bending moment, and the thrust force is equally distributed along the perimeter of the support. When the lateral pressure coefficient is not equal to 1.0, the sections at vault, invert, and springline, where the maximum bending moments located, are the most vulnerable. Welding steel at locations dominant by the bending moment is an effective way to improve flexural bearing capacity. The optimal flexural strengthening method for the support is welding steel at the vault and the springline, respectively, named ‘three-arcs welding.’

How Can Vernacular Construction Techniques Sustain Earthquakes: The Case of the Bhatar Buildings

After the 2005 M7.6 Kashmir earthquake (Pakistan), field observations reported that several buildings manufactured with local traditional techniques resisted well to that strong seismic event. In this paper the attention is focused on a typical vernacular construction technique commonly named as “Bhatar”, still practiced in the Himalayan regions of India and Pakistan. It is grounded upon the lacing or reinforcement masonry concept, i.e. the combination of dry-stacked loose stones with timber beams to increase the wall confinement. Despite its good seismic performances, it has still not been deeply studied from a structural engineering point of view. This paper represents a first attempt to fill this gap. It presents a full analytical study on the structural behaviour of a simple one-storey building unit characterized by a 3.6 m x 3.6 m square plan covered by an heavy wooden roof with 20 cm thick earth coverage, in order to investigate its response under gravity and seismic inertial loadings. Materials properties, static analysis and seismic analysis are discussed. In detail, Shorea Robusta wood and limestone rocks are identified as the most used construction materials for the Bhatar buildings. The Barton's model is applied to characterise the shear strength of the rubble stone layers in the wall. Static analysis reveals that normal stresses at the ground level are around 92 kPa, which can be considered acceptable for common soils. With respect to earthquake, the Bhatar technique can absorb wall cracking and distortion mechanisms, and can dissipate energy through friction between stones. Under the assumption of no vertical ground motion, the acceleration which activates in-plane sliding mechanisms is found to be around 0.5 g, being dependent on the interface friction between adjacent layers. Some preliminary considerations about the out-of-plane seismic behaviour are also provided concerning overturning and bending failure mechanisms. The results are based on assumptions taken by several authors and have not been verified with experimental tests. Nevertheless, some practical suggestions can be derived to improve the seismic shear strength and to ensure friction also in the case of significant vertical component of earthquake ground motions.

Bending failure mechanism and flexural properties of GLARE laminates with different stacking sequences

Failure mechanisms of GLARE laminates with different structure were investigated by the combination of experiment and numerical simulation methods to predict the damage behaviors of GLARE in practical applications. In this study, bending properties were obtained under varied experiment parameters. Results indicated that the value of span-to-thickness ratio (L/h ratio), which could change the failure mode of laminates, had the most significant impact on bending properties. Effective bending failure occurred when L/h ratio ranged from 14 to 24. Moreover, the bending properties of GLARE laminates with different structures such as 3/2 (3 aluminum sheets and 2 glass/epoxy plies), 4/3, 5/4 and 6/5 were measured and compared. The data revealed that bending modulus decreased with structural expansion. However, the bending strength of unidirectional laminates increased with structural expansion, while the bending strength of cross-ply laminates decreased. SEM observation showed that the failure of GLARE laminates consisted of elastic stage, plastic stage, local fracture of fiber layer and delamination stage.

Lightweight extrados restraining elements for the anti-seismic retrofit of single leaf vaults

Substantial vulnerability of single-leaf vaults has repeatedly been observed in the aftermath of past earthquakes. Major vault damage or even collapse may follow the onset of mechanisms such as the indirect bending of the vault crown caused by the unconstrained rocking of the abutments, the shear failure of the vault lunettes induced by possible differential rocking of the supporting masonries, and the direct differential bending induced by the inertia forces acting as a uniformly distributed horizontal load along the vault crown. Unlike other mechanisms, which can be inhibited by traditional global retrofit interventions aimed at triggering a box-like seismic response of the existing building, limiting direct bending requires targeted measures on the vault crown. In this paper, extrados lightweight plywood restraining structures applying passive confinement actions are conceived to delay the onset of the vault direct bending failure mechanism. The reinforcement is designed as a 3-hinged arch, hinged-constrained at the springing and at the vault key section to enable small relative displacements of the vault springing, which may follow the deformation of any internal ties or roof box structure. The technique is a lightweight and dry solution that does not require specialised labour; it is reversible and minimally impairs the structure’s integrity, thus respecting major restoration principles. The effectiveness of the solution is verified through an experimental study on the behaviour of a strengthened single-leaf vault, also in the case of possible relative displacements of the abutments. A special pivoting testing frame is conceived to apply cyclic, uniformly distributed inertia-like forces. The strengthened vault is shown to substantially outperform the response of an unreinforced single leaf vault, tested in a previous research study.

Failure mechanism of geosynthetic-encased stone columns in soft soils under embankment

The reaction of geosynthetic-encased stone columns (GECs) in soft soils under embankment loading was modeled with an indoor physical model test and numerical models using three dimensional and two dimensional finite element methods. The experimental and three dimensional numerical modeling results showed that the failure of the GECs is caused by the bending of the columns rather than shear. Three dimensional finite element analysis showed that the distribution of unbalanced lateral loading acting on the columns is symmetric about a ‘hinge point’ above the plastic hinge, rather than triangle or uniform distribution. An equivalent shear resistance model of the GECs is proposed based on the distribution of the unbalanced lateral loadings on the wall. The stability of the embankment was analyzed in two dimensional finite element method by transforming the columns into equivalent soil walls using equivalent bending resistance and equivalent shear resistance methods. It was found that results from equivalent bending resistance method is closer to the estimations from the three dimensional analysis, which agrees with the bending failure mechanism of the GECs. It is suggested that one more row of such columns may be required to provide higher lateral resistance in the soils in front of the toe to improve the stability of the embankment.