Damage Morphology Research Articles

Experimental study on the mechanical properties and uniaxial compressive constitutive relationship of sea sand coral concrete

The use of seawater, sea sand and coral to formulate concrete for marine engineering construction is an effective measure for rationally allocating resources and alleviating resource shortages. To promote the engineering application of marine concrete, it is necessary to study the mechanical properties and microstructure of marine concrete. In this study, sea sand coral concrete (SSCC) with strength grades of C20–C40 was prepared, and the compressive and flexural tests were conducted to observe the stress process and damage morphology of the specimens and to establish a constitutive model for SSCC under uniaxial compression. In addition, the microstructures of the SSCC hydration products and interfacial transition zone (ITZ) were observed via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the damage surface of the SSCC occurred directly through the coral aggregate, and the damage process was sudden and brief. Under uniaxial compression, the trend of the rising section of the stress-strain curve of SSCC with different strength grades are basically the same, but the shape of the descending section vary greatly, and the higher the strength grade is, the steeper the slope of the descending section. Quantitative relationships between compressive strength, elastic modulus, peak strain and peak stress and cube compressive strength were established. Based on the experimental results, a two-stage uniaxial compression constitutive model for SSCC was proposed, and the established constitutive model can effectively predict the stress-strain behavior of SSCC. In addition, the XRD patterns show that the early hydration rate of SSCC is faster than that of ordinary concrete (OC), which leads to a faster early strength development of SSCC. The SEM images show that the coral aggregate binds better to the cement matrix than the crushed gravel aggregate does and that the microstructure of the SSCC is denser than that of OC.

An insight into the mechanical behavior and failure mechanisms of T-stiffened composite structures with through-interface debonding defects

A robust 3D finite element model framework was established to capture the mechanical behavior and failure mechanisms of intact and through-interface debonding T-stiffened composite structures based on the progressive damage model and the cohesive zone model. Meanwhile, specimens with and without interface debonding defects were fabricated to validate the reliability and robustness of the proposed modeling framework. Finally, a parametric study was conducted on the types of interfacial debonding to further explore the effect on the buckling load, delamination initiation load, and ultimate load-carrying capacity of the composite stiffened structure. The results indicate that the load-carrying capacity of both single interface defects and double interface defects decreases gradually with increasing defect length and converges to a constant value. The reductions were 28.31% and 47.68%, respectively, compared to the intact structure. Interestingly, interfacial debonding has the most significant effect on the ultimate load at the 1/4 position. Moreover, interface debonding defects not only severely weaken the ultimate load-carrying capacity of the structure but also significantly alter the post-buckling path and failure mechanism, resulting in distinct degrees of deformation and damage morphology.

Surface damage induced by micropores in transparent ceramics under nanosecond laser irradiation.

The increasing use of transparent ceramics in laser systems presents a challenge; their low damage threshold has become a significant impediment to the development of powerful laser systems. Consequently, it is imperative to undertake research into the damage sustained by these materials. Micropores, the most common structural defects in transparent ceramics, inevitably remain within the material during its preparation process. However, the relationship between the density and size of these micropores and their impact on nanosecond laser damage threshold and damage evolution remains unclear. In this study, we utilize the annealing process to effectively manage the density and size of micropores, establishing a correlation between micropores in relation to damage thresholds. This study confirms for the first time that micropores significantly contribute to laser damage, comparing and analyzing the damage morphology characteristics of both front and rear surfaces of transparent ceramics. It also presents, potential mechanisms that may contribute to these differences in damage. This paper offers guidance for controlling micropores during the preparation and processing of transparent ceramics with high laser damage thresholds. The findings are expected to further improve the anti-nanosecond laser damage capabilities of transparent ceramics.

A high fidelity multiscale approach for compression-after-impact behavior of 2D triaxially braided composites

In the current study, limited research has been conducted on modeling high-velocity impacts and their effect on residual strength. Though the simulation of compression after low-velocity impact are mature, these methods still have some numerical issues when utilized in the case of high-velocity impacts. Thus, a brand-new method suitable for continuous simulation of compression after high-velocity impact was implemented. As for the modeling techniques for 2DTBC, both the research on the model structure and constitutive behavior is still crude and imprecise. To address this situation, a high fidelity multiscale approach which contains a more accurate RUC model, a strain rate sensitive viscoelastic constitutive model and a novel subcell model was established. The HVI and CAI examples were conducted based on this framework and most results showed an error of less than 5% in both the simulation of impact resistance and residual performance. Also, the damage morphologies of simulated results demonstrated its capability and effectiveness.

Author Correction: Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Author Correction: Damage morphology and force-deflection curves for impact loading of thick multilayer organic protective coating systems

Nanosecond laser damage of 532 nm thin film polarizers evaluated by different testing protocols

Different laser damage testing protocols, including 1-on-1, S-on-1, and Raster Scan, were conducted on 532 nm polarizers to evaluate the damage resistance and mechanisms. A comparison of the laser-induced damage thresholds (LIDTs) revealed different damage characteristics and major contributions to film failure for different polarizations. For P polarization, the LIDTs for the three test protocols were nearly the same because of the stabilization of two typical damage morphologies of flat-bottomed pits and mussel damage pits. For S polarization, the LIDTs for multiple pulses were lowest, where absorptive defect-induced damage was revealed. The damage characteristics of 532 nm polarizers and 1064 nm polarizers have been also compared. The mussel damage pits, which are similar to the typical damage morphologies of ultraviolet (UV) laser damage to fused silica, were observed for the first time in coatings of 532 nm polarizers. This suggests that, the polishing-induced subsurface damage of fused silica substrates may tend to be excited by a short-wavelength laser rather than the fundamental wavelength.

Experimental Study and Bearing Capacity Calculation of Compression-Reinforced Concrete Columns Strengthened with Ultra-High-Performance Concrete

A total of five ultra-high-performance concrete (UHPC)-strengthened reinforced concrete (RC) columns and one RC column were built and subjected to eccentric compression testing to examine the force performance of UHPC-strengthened eccentrically compressed plain RC columns. This experimental study examined the crack progression, the damage morphology, the deformation ability, the maximum load-carrying capacity, and the ductile properties of the eccentrically compressed columns. It also investigated the impacts of eccentricity, the reinforcement thickness, and the addition of steel fibers on the effectiveness of reinforcement. The cracking load, peak load, and ductility coefficient of the UHPC-reinforced specimens were increased by 100.28%, 172.30%, and 56.30%, respectively, compared with the RC column at an initial eccentricity of 50 mm. As the eccentricity distance increased, the bearing capacity of the UHPC eccentrically compressed specimens decreased, and the deformation capacity increased. Increasing the steel fiber dosage within the appropriate range decreased the crack width of the specimen. The addition of 2% steel fiber resulted in a 24.8% increase in cracking load, an 8.96% increase in peak load, and a 2.60% increase in ductility coefficient compared to the addition of 1% steel fiber. However, the reinforcing effect of UHPC was weakened under high eccentric pressures. Based on the theory of concrete structure and mechanical principles, the formula for calculating the compressive bearing capacity of RC columns strengthened with high-performance concrete was proposed. The results of calculating the positive section bearing capacity of eccentrically compressed RC columns reinforced with high-performance concrete are in good agreement with the test values. The results of this paper provide an experimental basis and theoretical foundation for the cross-sectional design of UHPC eccentrically compressed columns.

Strain rate effect of concrete based on split Hopkinson pressure bar (SHPB) test

Concrete is a strain rate sensitive material, which is widely used in protective structures, and its strain rate effect needs to be considered. This study aims to obtain the real strain rate effect of concrete material. Firstly, the dynamic compression test of concrete was carried out by using split Hopkinson pressure bar (SHPB). The classical Holmquist-Johnson-Cook (HJC) model of concrete is modified based on the test results and the test data of the static performance of concrete. Then the finite element model is established. The numerical simulation results and theoretical analysis show that the inertia effect leads to the error between the test value and the simulation value. To eliminate the influence of inertia effect, this study embeds the inertia effect term into the constitutive model for secondary modification. According to the results of numerical analysis, the specific form of this term and its related parameters are determined. The modified constitutive model can better predict the test results and reproduce the damage morphology of concrete under impact load.

Experimental and numerical investigation on the compression after high-velocity impact behavior of composite laminates

Considering the differences in damage mechanism between high-velocity impact (HVI) and low-velocity impact (LVI), this study conducted HVI tests and compression-after-impact (CAI) tests to reveal the post-impact compression behavior of laminates manufactured by unidirectional prepreg tape and exposed a completely different mechanical response in residual strength compared to that of LVI. By controlling the impact velocity within the range of 200 m/s ̃ 380 m/s, three kinds of impact results were obtained, including un-penetrated and penetrated conditions. Different CAI damage morphologies can be observed in these laminates. In order to fully understand the CAI damage mechanism induced by different HVI events, a surface-based cohesive behavior and a CDM intralaminar damage model were implemented. In addition, a more complete picture of the compression behavior after HVI was observed through the simulation results, which is of great help in estimating the residual strength of post-impact laminates. However, the HVI damage was introduced through the spherical steel projectiles, and the sample size was determined based on ASTM D7137, which might be different factors from the application conditions.

Study on the resistance of UHMWPE laminates against oblique penetration of projectiles

AbstractTo solve the problem of the wall panel of high‐performance shelters protecting against the oblique penetration of projectiles, ballistic experiments were carried out with ultra‐high molecular weight polyethylene (UHMWPE) laminates subjected to normal penetration by high‐velocity projectiles, and the deformation and failure characteristics of UHMWPE laminates were analyzed. The numerical model of the resistance of UHMWPE laminates against penetration of projectiles was established by using the finite element program LS‐DYNA. The validity of the numerical model was verified by the experimental results of damage morphology and the depth of depression of the target plate and the deformation of the warhead. On this basis, the ricochet angle and failure mode of the UHMWPE target plate against projectile penetration were studied numerically, and the impact of the angle of incidence on the residual kinetic energy and normal penetration displacement of the bullet, as well as the damage morphology of the UHMWPE target plate, was revealed by using simulation. The results showed that the ricochet angle of the bullet obliquely penetrating into the UHMWPE target plate was in the range of 45° to 50°; at the initial stage of projectile penetration, the shear fracture failure of the fiber layer mainly occurred at the striking face of the UHMWPE target plate. Under the impact of the warhead deformation, with the reduction of the residual velocity of the bullet, the failure mode gradually changed to the tensile and interlaminar cohesion failure of the fiber layer near the back face; When the angle of incidence was greater than the ricochet angle, the residual kinetic energy of the projectile increased slowly with the increase of the angle of incidence of the bullet and then went up approximately linearly; the normal displacement of the bullet obliquely penetrating into the UHMWPE target plate decreased slowly after reaching the peak, and the peak value of the normal penetration displacement decreased gradually with the increase of the angle of incidence, and the time to peak of the displacement shortened gradually. The damage area of the bulge on the back surface of the UHMWPE target plate after penetration decreased gradually with the increase of the angle of incidence. The research results can provide a theoretical reference for the application of UHMWPE laminates in the design of military bulletproof shelters and armor.

Prospecting the Potential of Plant Growth-Promoting Microorganisms for Mitigating Drought Stress in Crop Plants.

Drought is a global phenomenon affecting plant growth and productivity, the severity of which has impacts around the whole world. A number of approaches, such as agronomic, conventional breeding, and genetic engineering, are followed to increase drought resilience; however, they are often time consuming and non-sustainable. Plant growth-promoting microorganisms are used worldwide to mitigate drought stress in crop plants. These microorganisms exhibit multifarious traits, which not only help in improving plant and soil health, but also demonstrate capabilities in ameliorating drought stress. The present review highlights various adaptive strategies shown by these microbes in improving drought resilience, such as modulation of various growth hormones and osmoprotectant levels, modification of root morphology, exopolysaccharide production, and prevention of oxidative damage. Gene expression patterns providing an adaptive edge for further amelioration of drought stress have also been studied in detail. Furthermore, the practical applications of these microorganisms in soil are highlighted, emphasizing their potential to increase crop productivity without compromising long-term soil health. This review provides a comprehensive coverage of plant growth-promoting microorganisms-mediated drought mitigation strategies, insights into gene expression patterns, and practical applications, while also guiding future research directions.

Effect of particle size distribution on the cryogenic mechanical properties of triple‐base propellants

AbstractFillers play a decisive role in the mechanical properties of polymer composites. In this paper, different particle sizes of nitroguanidine were obtained to regulate the internal filler structure of triple‐base propellants (TBP) to improve their mechanical response in different environments. A series of morphological and structural characterizations on nitroguanidine (NQ) particles were conducted using techniques. The results indicated that the obtained NQ particles maintained a high level of crystalline quality while preserving their molecular integrity. The mechanical properties of TBP were systematically evaluated under various loading conditions, including cryogenic tensile, compressive, and impact loads, as well as dynamic thermomechanical effects. Additionally, three‐point bending simulations were employed to elucidate the mechanical responses and damage mechanisms. Under axial tensile and compressive loads, reducing the particle size of NQ significantly enhanced the tensile and compressive strength. The maximum tensile strength and compressive strength can reach 344.62 MPa and 104.79 MPa. Moreover, the compressive failure mode transitioned from cracking to axial shrinkage. Conversely, when subjected to radial bending loads, TBP exhibited contrasting behavior, including a decrease in the glass transition temperature from 84.73°C to 76.93°C and a non‐monotonic trend in impact strength (initially increasing from 4.96 to 8.85 kJ/m2 and then decreasing to 2.27 kJ/m2). This study provides valuable insights into the mechanical performance of TBP, supporting the development of high‐energy, high‐strength TBP formulations.Highlights SEM analysis confirms the pronounced orientation effect of rod‐like NQ. The orientation and particle size of NQ decide TBP's radial impact resistance. Submicron NQ enhances the compression resistance property of TBP. Submicron NQ brings about a shift in the microscopic damage morphology of TBP.

Tensile impact behaviors and damage mechanism of woven carbon fiber-reinforced-polymer laminates considering adiabatic shear band

In this study, the tensile impact behavior and damage mechanism of a two-dimensional woven carbon-fiber-reinforced-polymer (CFRP) laminates under different high strain rates are investigated. The damage morphologies are illustrated and studied using meso-macroscale finite element analysis (FEA) and Split Hopkinson bar (SHB) test, FEA results are compared and validated with the SHB test results, and proved to be correct with enough accuracy. The matrix crack first appeared, the tensile stress wave propagated along the interface, which causes shear failure at the interface, which dominated the failure of the specimen and formed adiabatic shear bands inside each ply, the adiabatic shear bands begin to develop in areas with interfacial damage, they are formed after structural damage and propagate in the direction of the interface, accompanied by damage evolution. High strain rate 1400, 1600, and 2400 s−1 impacts tend to lead to direct failure of composite laminates compared to low strain rate 600, and 800 s−1 impacts, the Young’s modulus with high strain rate 1400, 1600, and 2400 s−1 are more than twice as much compared to low strain rate 600, and 800 s−1. The plain-woven CFRP laminates is characterized with strain-rate-hardeningeffect and strain rate sensitivity, with increase of high strain rate from 600 to 2400 s−1, the Young’s modulus increases from 8.91 to 35.7 GPa, whereas the yield strength increases from 397 to 1298 MPa. The delamination occurs between the plies after crack generation inside the epoxy resin matrix, and begins at a certain strain value after the elastic phase, the micro-cracks propagated along the fiber bundle-matrix interface, thus causing interfacial debonding due to shear stress, these factors result in a strain-rate hardening effect.

Damage Behavior with Atomic Force Microscopy on Anti-Bacterial Nanostructure Arrays

The atomic force microscope is a versatile tool for assessing the topography, friction, and roughness of a broad spectrum of surfaces, encompassing anti-bacterial nanostructure arrays. Measuring and comparing all these values with one instrument allows clear comparisons of many nanomechanical reactions and anomalies. Increasing nano-Newton-level forces through the cantilever tip allows for the testing and measuring of failure points, damage behavior, and functionality under unfavorable conditions. Subjecting a grade 5 titanium alloy to hydrothermally etched nanostructures while applying elevated cantilever tip forces resulted in the observation of irreversible damage through atomic force microscopy. Despite the damage, a rough and non-uniform morphology remained that may still allow it to perform in its intended application as an anti-bacterial implant surface. Utilizing an atomic force microscope enables the evaluation of these surfaces before their biomedical application.

Comparison of two progressive damage models for predicting low-velocity impact behavior of woven composites

This research focuses on comparing the two progressive damage models available in the explicit nonlinear finite element software LS-Dyna. To explore the prediction capabilities in terms of mechanical response and dominating failure modes in S2 glass woven composites, low velocity impact response at four different energies ranging from 27.9 J to 109.7 J were considered in this study. A macro-homogeneous solid element formulated finite element model was simulated to understand the response and failure mechanics in the laminate under low-velocity impact. The material modeling was carried out utilizing the MAT 55 and MAT 162 material models. An effort has been made for robust calibration of the various physical and non-physical parameters in both material cards for accurate predictions. The prediction capabilities of the models were then examined by comparing them against the experimental results, which fall within the deviation of ∼11%. The results show that MAT 162 yields a better resemblance with the damage morphology patterns and the delamination for the accounted impact zone, due to inclusion of strain-rate effect. Overall, this paper provides insight into the limitations and advantages of both material models, which establishes the route for the selection of the appropriate material model for simulating impact behavior in woven composites.

Effect of interlaminar basalt fiber veil reinforcement on mode I fracture toughness of basalt fiber composites

AbstractComposite structures are vulnerable to delamination under out‐of‐plane loading due to the absence of reinforcing fibers in the thickness direction. This paper introduced the interlaminar basalt fiber veil technique to improve the interlaminar fracture toughness of basalt fiber‐reinforced thermoplastic composite laminates. The reinforcement effect of the basalt fiber veil on GIC of composite laminates was investigated by a double cantilever beam (DCB) test. The toughening effect, damage morphology, and the basalt fiber veil toughening mechanism were analyzed by mechanical response, optical photos, and scanning electron microscopy (SEM). It was found that the basalt fiber veil could significantly inhibit the propagation of interlaminar cracks. Compared to the unreinforced specimen, the maximum load of basalt fiber veil‐reinforced laminate was increased by 73%, the average platform load was increased by 72.7% and the GIC was increased by 157%.Highlights Improvement of GIC of basalt fiber‐reinforced thermoplastic laminates by basalt fiber veil. The toughening mechanism for the basalt fiber veil. The GIC of the fiber veil‐reinforced laminate was 157% higher than the unreinforced laminate.

Experimental and numerical investigation on bearing behavior of hybrid thin/thick-ply composite laminates

Experimental and numerical studies were carried out to characterize hybrid thin- and thick-ply composite laminates and assess modelling capabilities. Five different composite laminates were manufactured using a single material system with varying proportions of thin plies (0%, 50%, and 100% thin-ply). Bearing tests were performed and the results from the tests were investigated. The results showed that performance, in terms of bearing strength at onset of damage and ultimate bearing stress, increased proportionally with the increasing amount of thin plies within the laminate. Microscopic examination of the failure modes for all laminates was performed at the center of the hole to determine the dominant failure mode. The numerical investigation uses a highly detailed mesoscale model previously validated for crash simulations but never used successfully to bearing damage areas. The results showed a good correlation regarding both the load response and the morphology of damage.

A whole service time SHM damage quantification model hierarchical evolution mechanism

Accurate damage quantification for an individual aircraft by using structural health monitoring (SHM) technology poses a persistent challenge in practical engineering. Existing damage quantification models typically rely on prior data acquired from ground design and tests. However, an individual aircraft is subject to diverse uncertainties throughout its whole service time, such as time-varying environmental and operational conditions, different flight missions, and different damage morphologies. Consequently, employing a prior trained model for damage quantification inevitably introduces errors, thereby limiting the engineering applicability of SHM. To improve the damage quantification accuracy for individual aircraft under the influence of uncertainty, a new whole lifetime data-based damage quantification model hierarchical evolution mechanism is proposed in this paper. Multi-source data from the design, service, and maintenance stages of individual aircraft are adopted to continuously evolve the probabilistic damage diagnosis model, enabling it to characterize the specific data distribution and track the damage propagation. The proposed method is validated through fatigue tests of a landing gear beam structure, which is an important aircraft load-carrying component, with guided wave monitoring based hidden Markov model quantifying its crack propagation. The validation result demonstrates the effectiveness of the proposed method in ensuring the long-term reliability of the model and achieving more accurate damage quantification for an individual aircraft.

Experimental study and finite element analysis on axial compression performance of CFRP-PVC confined coral seawater and sea-sand concrete columns

In this paper, a composite column using carbon fibre reinforced plastics and polyvinyl chloride composite tube (CFRP-PVC) to constrain coral aggregate seawater sea-sand concrete (CSSC) was proposed, and CFRP was pasted on the inner and outer walls of the PVC tube. To investigate the effects of the number of CFRP layers and void defects on the axial compression performance of PVC tubes, six specimens were made for axial compression loading tests and finite element parameter analysis. The results indicate that due to PVC improving the integrity of CFRP, PVC tube provide a stress transfer path for CFRP, placing CSSC in a triaxial compression state. When both the inner and outer walls of the tube are pasted with CFRP, brittle failure of CFRP-PVC tube can be effectively avoided and have relatively superior mechanical properties. In the same situation, when one layer of CFRP is pasted on the inner wall of the tube, it has better ductility and bearing capacity. When two layers of CFRP are pasted on the outer wall of the tube, the coefficient of constraint stress increase is as high as 121.5%, and the void defect only has a significant impact on ductility. A finite element model of CFRP-PVC confined CSSC columns considering Hashin damage criterion was established based on ABAQUS, accurately predicting the failure process and CFRP damage morphology of test columns under axial load. Parameter analysis shows that when the confinement coefficient of CFRP-PVC confined CSSC columns is less than 0.3 and the height-diameter ratio is greater than 15, the load-displacement curve will lose the strengthening stage, and increasing the number of outer CFRP layers will slightly increase the stiffness of the strengthening stage. A bearing capacity calculation method suitable for CFRP-PVC confined CSSC was proposed based on the model of steel tube confined concrete, with an error of 1.2%.

Diagnosis and root cause analysis of bearing failure using vibration analysis techniques

This paper is presented to diagnose and root cause analysis of the bearing failure. For this purpose, a vibration investigation was carried out on a motor with a 2300 kW power, 1489 rpm speed. Bearing failure was diagnosed by trending and analyzing vibration parameters. By investigating the bearing damage morphologies, a false brinelling pattern was observed. To find the failure cause, the machine was evaluated for two aspects; vibrations and lubrication. The resonance in the fan and the lack of full lubrication film formation were considered root causes of failure. To mitigate resonance, changing the operating speed was considered as a corrective action. By increasing the operating speed (1491 to 1530), the vibration amplitude decreased by nearly 21%. Also, the thickness of the lubricating film was improved by installing an airflow hose. Using this method, the time between failures increased from 3 to 11 months.