Compressive Failure Mechanism Research Articles

Study on the compressive strength and failure mechanism of fiber-reinforced polymer green filling materials

The utilization of industrial solid waste in the preparation of geopolymer filling materials offers benefits such as low carbon emissions and resource conservation showcasing broad application prospects. In this study, geopolymer filling materials are prepared using calcium carbide slag, slag, fly ash, and tailings, with the addition of 12 mm polypropylene fibers to enhance their strength and toughness. Conducting UCS experiments to investigate the effects of different calcium carbide slag content, fiber content, and water-solid ratio on the UCS of the materials; Utilizing SEM-EDS and XRD techniques to analyze the mechanisms of strength formation in filling materials and the mechanisms of fiber toughening and crack resistance at the micro level; Establishing a uniaxial compression test model using discrete element PFC 3D software and combining digital speckle technology to visually analyze the sample's failure process. The research results indicate that the stimulation of slag and fly ash by calcium carbide slag results in a large amount of C-(A)-S-H gel, effectively promoting the bond between aggregate and fiber, with the UCS of the samples gradually increasing with the addition of calcium carbide slag. With the increase in fiber content, the UCS of the samples shows a trend of first increasing and then decreasing, with the optimal fiber content being 6 ‰. The fibers exist in the matrix in the form of anchor rods and a three-dimensional network structure, playing a good reinforcing role and effectively inhibiting the expansion and development of cracks; The crack morphology of the samples in the PFC 3D numerical simulation process is close to the digital speckle failure morphology, and the axial load-displacement curve in the numerical simulation aligns well with the indoor test results. The research results can provide theoretical guidance for the preparation of fiber-reinforced green filling materials using all solid waste.

Acoustic Emission characteristics and damage evolution of Concrete-Encased CFST columns under compressive load

Concrete-Encased Concrete Filled Steel Tubular (CE-CFST) is usually served as a compression member in engineering structures due to its high performance. It is crucial to reveal its compressive failure mechanism and the damage evolution law. This study used Acoustic Emission (AE) technology to monitor the compressive failure behavior of seven groups of CE-CFST columns with different diameter-width ratio, slenderness ratio and eccentricity, and then the AE signal characteristics and structural damage evolution law were discussed. Results show that the curve of AE characteristics can be used for effectively identifying the damage stages of CE-CFST structures. The failure process can be divided into six stages: initial compaction, stable growth of micro cracks, unstable propagation of macro cracks, collapsing of the outer RC structure, bulging of the core CFST structure and overall failure. The AE characteristic parameters, RA-AF value and b value are closely related to stress and crack of structure, and can be used for early warning of structural failure during the stage of unstable crack propagation. Particularly, the failure of outer concrete can be judged as b value drops to the minimum. The current study is of great significance for understanding the damage evolution process and achieving damage assessment of CE-CFST structures.

Failure Behavior and Mechanism of Vat Photopolymerization Additively Manufactured Al2O3 Ceramic Lattice Structures

Vat photopolymerization additive manufacturing produces lightweight load-bearing ceramic lattice structures that have flexibility, time-efficiency, and high precision, compared to conventional technology. However, understanding the compression behavior and failure mechanism of such structures under loading remains a challenge. In this study, considering the correlation between the strut angle and bearing capacity, body-centered tetragonal (BCT) lattice structures with varying angles are designed based on a body-centered cubic (BCC) structure. BCT Al2O3 ceramic lattice structures with varying angles are fabricated by vat photopolymerization. The mechanical properties, deformation process, and failure mechanism of the Al2O3 ceramic lattice structures are characterized through a combination of ex- and in-situ X-ray computed tomography (X-CT) compression testing and analyzed using a finite element method (FEM) at macro- and micro-levels. The results demonstrate that as the angle increases, the stress concentration gradually expands from the node to the strut, resulting in an increased load-bearing capacity. Additionally, the failure mode of the Al2O3 ceramic lattice structures is identified as diagonal slip shear failure. These findings provide a greater understanding of ceramic lattice structure failures and design optimization approaches.

Multiscale study on compressive failure mechanism of plain woven composites considering stochastic waviness defects

This work proposes a multiscale correlation algorithm based on structural level to study the compression damage behavior of plain woven composites. The multiscale algorithm includes a homogenization process that establishes the mesoscale constitutive relationship based the mechanical properties of microscopic constituent to derive the macro-mechanical response, and a localization process that constructs a mapping relationship among mesoscale stress, microscale stress and micro-component failure based on the macroscale load. The results of uniaxial compression experiments are used to validate the model. The multiscale model combined with micro-mechanics of failure (MMF) and 3D kinking model accurately predict the effective stiffness, ultimate compressive strength, damage modes and fracture characteristics. With increasing compression load, the matrix damage of yarn, fiber kinking and pure matrix damage successively initiate. Furthermore, the effect of yarn waviness defects deviating from the ideal design on compressive mechanical behavior is parametrically investigated based on the hypothesis of Gaussian distribution for defects. The increase of waviness misalignment angle (the difference between actual and ideal waviness angle) and its dispersion degree reduces the compression modulus and failure strength. Therefore, the influence of stochastic waviness defects on mechanical response cannot be ignored in structural level design and application of woven composites.

Compressive failure of thermally strengthened glass spheres — Why are Prince Rupert's drops so strong?

This paper aims to elucidate the exceptional high strength of Prince Rupert's Drops (PRDs). PRDs are idealized as thermally strengthened Glass Spheres (SGSs), and their compressive failure mechanisms are investigated experimentally and numerically. The distributions of residual stress within SGS specimens are quantitatively characterized using an integrated photo-elastic method. Uniaxial compression tests conducted on these specimens reveal that the compressive residual stress present on the sphere's surface significantly enhances its strength. High-speed video images demonstrate that SGSs fail at the equatorial region, in contrast to annealed glass spheres (AGS) which typically fracture near the Hertzian contact zone. Numerical simulations suggest that the residual stress mitigates the maximum principal stress on the surface of SGSs, thereby impeding the development of flaws on the surface of the specimens. Ultimately, failure of SGS specimens under pressure occurs due to the “squeezing” effect, in contrast to AGSs which commonly fail due to contact indentation.

Compressive Failure Characteristics of 3D Four-Directional Braided Composites with Prefabricated Holes.

The low delamination tendency and high damage tolerance of three-dimensional (3D) braided composites highlight their significant potential in handling defects. To enhance the engineering potential of three-dimensional four-directional (3D4d) braided composites and assess the failure mode of hole defects, this study introduces a series of 3D4d braided composites with prefabricated holes, studying their compressive properties and failure mechanisms through experimental and finite element methods. Digital image correlation (DIC) was used to monitor the compressive strain on the surface of materials. Scanning acoustic microscope (SAM) and scanning electron microscopy (SEM) were used to characterize the longitudinal compression failure mode inside the material. A macroscopic model is established, and the porous materials are predicted by using the general braided composite material prediction theory. While reducing the forecast cost, the error is also controlled within 21%. The analysis of failure mechanisms elucidates the damage extension mode, and the porous damage tolerance ability aligns closely with the bearing mode of braided material structure. Different braiding angles will lead to different bearing modes of materials. Under longitudinal compression, the average strength loss of 15° specimens is 38.21%, and that of 30° specimens is 8.1%. The larger the braided angle, the stronger the porous damage tolerance. Different types of prefabricated holes will also affect their mechanical properties and damage tolerance.

Study on Low-Velocity Impact and Residual Compressive Mechanical Properties of Carbon Fiber-Epoxy Resin Composites.

Room temperature drop hammer impact and compression after impact (CAI) experiments were conducted on carbon fiber-epoxy resin (CF/EP) composites to investigate the variation in impact load and absorbed energy, as well as to determine the residual compressive strength of CF/EP composites following impact damage. Industrial CT scanning was employed to observe the damage morphology after both impact and compression, aiding in the study of impact-damage and compression-failure mechanisms. The results indicate that, under the impact load, the surface of a CF/EP composite exhibits evident cratering as the impact energy increases, while cracks form along the length direction on the back surface. The residual compressive strength exhibits an inverse relationship with the impact energy. Impact damage occurring at an energy lower than 45 J results in end crushing during the compression of CF/EP composites, whereas energy exceeding 45 J leads to the formation of long cracks spanning the entire width of the specimen, primarily distributed symmetrically along the center of the specimen.

Compressive strength and failure mechanism of high-modulus carbon fibers produced from polyacrylonitrile and mesophase pitch

Compressive strength and failure mechanism of high-modulus carbon fibers produced from polyacrylonitrile and mesophase pitch

Compressive failure mechanisms in unidirectional fiber reinforced polymer composites with embedded wrinkles

The present study examines how wrinkles affect a composite material’s compressive failure behavior. Uni-directional carbon fiber-reinforced polymer (UD-CFRP) composites with artificially induced wrinkles were fabricated by placing laminate strips in specific positions. The geometry and placement of these strips were varied, resulting in 18 different wrinkle configurations. Through extensive experimental testing, it was observed that the compressive strength decreased significantly, ranging from 20% to 73%, depending on the specific wrinkle configuration. The experimental results were found to align well with existing analytical models. Additionally, the study examined how the wrinkle characteristics affected the final kink bandwidth, angle, and inclination. Fractographic studies on the failed specimens revealed various damage modes at different length scales, including kinking, delamination, buckle delamination, crushing, fiber pullout, matrix cracking/failure, and fiber failure. Based on these findings, it is emphasized that the geometry of the wrinkles and the aforementioned damage modes at different length scales must be accounted for while developing a numerical model to predict the compressive behavior of the composite accurately.

Enhanced compressive mechanical properties of different topological lattice structures fabricated by additive manufacturing

This study focuses on the mechanical properties of 316 L stainless steel lattice structures. Three types of lattice structures with varying topology cells were designed and fabricated by additive manufacturing (AM) techniques. The experimental test and numerical simulation were employed to investigate compressive response and failure mechanisms of lattice structures. The results indicate that decreasing the porosity or unit cell size of lattice structures can significantly improve mechanical performance. Furthermore, it is noted that lattice structures with face-centered cubic with(vertical) Z-struts (FCCZ) cells exhibit the highest elastic modulus, compressive strength, and energy absorption, along with distinct failure modes in comparison to other types of lattice structures.

Mechanical behavior of eccentrically loaded UHPC-encased CFST medium-long columns

To study the eccentric compression performance and failure mechanism of ultra-high performance concrete (UHPC) encased concrete-filled steel tubular (CFST) medium-long columns (UC-CFST medium-long columns), a total of 27 UC-CFST column specimens were tested under eccentric compression with eccentricity and slenderness ratio as the main parameters. After verified by experimental results, the finite element (FE) analysis of UC-CFST medium-long columns with actual structural cross-sectional size under eccentric compression was further carried out. It is found that as the slenderness ratio and eccentricity increased, the bending stiffness and the ultimate bearing capacity of the UC-CFST columns decreased gradually, and the failure mode changed from strength failure to instability failure, and the smaller the proportion of encasing UHPC area, the greater the upper-bound slenderness ratio of strength failure. Moreover, the influence of eccentricity was nonlinearly coupled with slenderness ratio on the eccentric compressive bearing capacity of UC-CFST medium-long columns. Finally, a calculation method of ultimate load-bearing capacity of UC-CFST medium-long columns considering the influence of eccentricity and slenderness ratio was proposed, which had good calculation accuracy with experimental and numerical results.

Computational analysis of the failure mechanisms of a laminated composite in double-edge notch compression configuration

This manuscript presents a combined experimental–computational investigation of the compression failure response of laminated composites in double-edge notch compression (DENC) configuration. Analysis of in-situ and post-test DENC experiment results indicates the presence of multiple failure mechanisms, including ply splitting, delamination, and compression kink bands. In order to characterize the onset, growth, and interplay of the critical and subcritical damage mechanisms, a multiscale progressive damage analysis approach is implemented. A nonlocal multiscale damage model explicitly tracks the intraply failure mechanisms that lead to the formation and propagation of kink bands in the specimen. A cohesive zone model is used to track initiation and progression of ply splitting in the specimen. The splitting model was implemented using implicit finite element simulations and deployed with a pre-crack insertion technique to reduce simulation time while preserving prediction accuracy. Model parameters are calibrated based on available calibration data and measurements. The effects of split location and growth characteristics on model predictions are studied. The computational model along with a suite of experiments were employed to study the formation, growth and interactions of damage mechanisms in the composite specimens subjected to compression loading. The onset of matrix damage is not clear from the experimental images but the model predicts early onset around the onset time of splits which greatly reduce the stress concentration at the notches. Analysis of acoustic emission energy experimental data indicate that observable compression failure mechanisms are not causing nonlinearity consistently exhibited in the experiment responses. Simulation results demonstrate the capability of the multiscale modeling approach to predict critical kink bands and sub-critical matrix cracking and splitting in the DENC specimens while reducing computational cost compared to a direct numerical simulation of fibers and matrix.

Micromechanical modeling of longitudinal compression behavior and failure mechanism of unidirectional carbon fiber reinforced aluminum composites involving initial fiber misalignment

AbstractA micromechanical model with realistic initial fiber misalignment (IFM) was developed to simulate the longitudinal compression behavior of unidirectional carbon fiber/aluminum composites. The matrix and fiber were modeled using ductile damage law and brittle fracture model, respectively. The interfacial properties were firstly determined by the single‐fiber push‐out and transverse tensile tests, and the cohesive zone model was adopted to capture the interfacial behavior. The calculated compressive response curve is in alignment with the experimental data. Compression failure can be attributed to fiber kinking, possibly triggered by the matrix shear damage. The increase of IFM angle makes the failure mode being transformed from fiber crushing to fiber kinking, along with a significant decrease in compressive strength. With the fiber content increasing, the compressive strength increases first and then decreases, while the compressive modulus increases monotonically. Increasing interfacial strength significantly improves the compressive strength, but this is limited by the matrix properties.

Residual strength and failure mechanism of CF/PPS composites with delamination damage

AbstractDelamination is one form of damage in composite laminates. The effects of delamination damage locations (thickness direction of laminates) on the residual compressive strength and failure mechanism of carbon fiber/polyphenylene sulfide (CF/PPS) composites are studied by damage morphology, full‐field strain and finite element simulation. The closer the delamination is to the center of the composite, the lower the residual compressive strength. The failure mode of composites is dominated by 0° fiber fracture, which is divided into bulging, delamination propagation, and fracture. The delamination locations significantly affect the first two stages.Highlights Constructing delamination damage in composites by interlayer preset defects. Simulation and damage analysis to reveal the mechanism of compression failure. The relationship between delamination depth and damage stage is revealed.

Mesoscale Model for Composite Laminates: Verification and Validation on Scaled Un-Notched Laminates.

This paper presents a mesoscale damage model for composite materials and its validation at the coupon level by predicting scaling effects in un-notched carbon-fiber reinforced polymer (CFRP) laminates. The proposed material model presents a revised longitudinal damage law that accounts for the effect of complex 3D stress states in the prediction of onset and broadening of longitudinal compressive failure mechanisms. To predict transverse failure mechanisms of unidirectional CFRPs, this model was then combined with a 3D frictional smeared crack model. The complete mesoscale damage model was implemented in ABAQUS®/Explicit. Intralaminar damage onset and propagation were predicted using solid elements, and in-situ properties were included using different material cards according to the position and effective thickness of the plies. Delamination was captured using cohesive elements. To validate the implemented damage model, the analysis of size effects in quasi-isotropic un-notched coupons under tensile and compressive loading was compared with the test data available in the literature. Two types of scaling were addressed: sublaminate-level scaling, obtained by the repetition of the sublaminate stacking sequence, and ply-level scaling, realized by changing the effective thickness of each ply block. Validation was successfully completed as the obtained results were in agreement with the experimental findings, having an acceptable deviation from the mean experimental values.

In-plane compressive properties and failure mechanisms of gradient Cf/ZrB2–SiC composites in high-temperature environment

The gradient Cf/ZrB2–SiC composites can exert the dual advantages of low-density and excellent heat resistance, but which have the complex mechanical properties due to the inhomogeneous geometry characteristics. The in-plane compressive behavior and failure analysis can examine the material integrity and the effect of inhomogeneous characteristics. The in-plane compressive elastic modulus distribution is expressed mathematically by using the superficial elastic modulus, back elastic modulus, and the gradient pore distribution. The superficial elastic modulus and the gradient pore distribution of the gradient materials were characterized by nanoindentation test and Micro-CT statistics. The back of the gradient materials is the porosity needled C/C composites without introducing ZrB2–SiC matrix, whose elastic modulus can be referenced from our previous work. The in-plane compressive experiments of the gradient materials in the high-temperature environment were also conducted to study the failure mechanisms. The strength of the gradient materials is further revealed by the temperature-dependent properties of carbon fibers and thermal residual stress release. The results indicate the gradient structure can effectively eliminate the delamination damage, but the high temperature drastically weakens the ability of needled fibers suppressing delamination damage in the high-porosity region of the gradient materials. This study can be helpful to the material design and evaluation of mechanical properties for the gradient Cf/ZrB2–SiC composites.

Optimisation of printing parameters of fused filament fabrication and uniaxial compression failure analysis for four-point star-shaped structures

PurposeThe purpose of this paper is to present an optimisation of four-point star-shaped structures produced through additive manufacturing (AM) polylactic acid (PLA). The study also aims to investigate the compression failure mechanism of the structure.Design/methodology/approachA Taguchi L9 orthogonal array design of the experiment is adopted in which the input parameters are resolution (0.06, 0.15 and 0.30 mm), print speed (60, 70 and 80 mm/s) and bed temperature (55°C, 60°C, 65°C). The response parameters considered were printing time, material usage, compression yield strength, compression modulus and dimensional stability. Empirical observations during compression tests were used to evaluate the load–response mechanism of the structures.FindingsThe printing resolution is the most significant input parameter. Material length is not influenced by the printing speed and bed temperature. The compression stress–strain curve exhibits elastic, plateau and densification regions. All the samples exhibit negative Poisson’s ratio values within the elastic and plateau regions. At the beginning of densification, the Poisson’s ratios change to positive values. The metamaterial printed at a resolution of 0.3 mm, 80 mm/s and 60°C exhibits the best mechanical properties (yield strength and modulus of 2.02 and 58.87 MPa, respectively). The failure of the structure occurs through bending and torsion of the unit cells.Practical implicationsThe optimisation study is significant for decision-making during the 3D printing and the empirical failure model shall complement the existing techniques for the mechanical analysis of the metamaterials.Originality/valueTo the best of the authors’ knowledge, for the first time, a new empirical model, based on the uniaxial load response and “static truss concept”, for failure mechanisms of the unit cell is presented.

Rate-dependent damage and failure behavior of lithium-ion battery electrodes

The mechanical properties and failure behavior of composite electrodes are critical to understanding the internal short circuits and ensuring the crush safety of lithium-ion batteries used in electric transportation. This study provides a comprehensive experimental investigation into the strain rate–dependent tensile/compressive behavior and failure mechanism of both anode and cathode, covering a range from quasi-static to dynamic conditions. A universal testing machine equipped with an industrial camera was used to assess the mechanical properties and observe the deformation process of the electrodes under quasi-static conditions. Additionally, a split Hopkinson bar system, coupled with a high-speed camera, was utilized to evaluate the mechanical properties and capture the deformation process of the electrodes under dynamic loading. The detailed deformation and failure modes of the electrodes were revealed by a combination of post-mortem characterization and images from high-speed cameras. The experimental results demonstrate a significant strain rate effect on the tensile and compressive mechanical behavior and failure mechanism of both anode and cathode. The rate dependence of tensile/compressive strength and failure strain were discussed, and the underlying mechanism for strain rate sensitivity was analyzed. The results and conclusions from this study provide an important foundation for the detailed modeling and failure prediction of lithium-ion batteries under impact loading. Further, these findings facilitate the safety design of electric vehicles by informing to enhance crash safety.

A micro-theoretical model for predicting the unconfined compressive strength of cement-sand reinforced soft clay

Cement-sand reinforced soft clay (C-SRSC) is a complex multiphase geomaterial. Its strength is determined by the physical properties of the internal multiphase substances and the coupling mechanical response between various phases of substances. By considering the effect of the particle size and content of sand particles on the unconfined compressive strength (UCS) and failure mechanism of C-SRSC, the C-SRSC is divided into two phases of the cement soil matrix and sand particles to construct a micro cell model of C-SRSC. Based on the strain gradient theory, the theoretical model of the UCS of C-SRSC based on the physical mechanism at the microscale is derived. Forty five groups of UCS tests were conducted to analyze the effect of sand particle size and content on the UCS of C-SRSC, and to calculate the theoretical model parameters. The results show that the UCS of C-SRSC increases with increasing curing age, cement content, and sand particle content, and decreases with the increasing sand particle size. The theoretical model of the UCS of C-SRSC based on physical mechanism initially verified the consistency of the experimental and theoretical results.

The effects of temperature and hygrothermal aging on the properties of CF/PA6 composite and its compression failure mechanisms

AbstractCarbon fiber reinforced polyamide composites have outstanding properties, but their applications are significantly affected by the service environment. This work evaluates the effects of temperature (25, 80, 140, and 200°C) and hygrothermal conditions on the mechanical properties of CF/PA6 composite containing delamination damage, and studies its damage behaviors and failure mechanisms. After hygrothermal aging, recrystallization of PA6 improves the heat resistance of CF/PA6 composites, but water absorption reduces the interfacial strength of composites, resulting in the decrease of modulus and compressive strength (24% and 42%, respectively). With the increase in temperature, the compressive strength of CF/PA6 composites gradually decreases (from 132 MPa at 25°C to 24 MPa at 200°C), and the failure mode transitions from fiber fractures, interlayer shear fractures, delamination to kinking. In addition, the compressive failure process of CF/PA6 composites is divided into three stages: buckling, delamination bulging and kinking failure.Highlights Hygrothermal aging reduces the fiber/resin interface performance. Fiber fracture, interlayer shear and delamination convert to kinking failure. The failure process is divided into buckling, delamination and kinking.