Critical Failure Load Research Articles

Fractal, tribo-mechanical and corrosion characterization of hydrophobic and lead free electroless Ni-B mono and bi-layer coating developed using artificial intelligence

Abstract A quaternary, lead free electroless Ni-B-Cu-Sn coating was obtained using experimental design, artificial neural network and genetic algorithm based on higher hardness and deposition rate. A high predicted as-deposited hardness of 1138 HV0.05 and deposition rate of 10 μm hr−1 was achieved. Coating surface had nodular, self-similar fractal nature with higher density for the bi-layered variant. The surface roughness and tribological behaviour was better for the single layered coating. Adoption of double layered coating only had a mild improvement in the corrosion resistance. The bi-layered coatings also exhibit hydrophobic nature with contact angle ∼121°–130°. The first critical load of failure of both the coatings were around 20 N which is nearly like lead stabilized electroless Ni-B coating. This new coating variant can possibly be a newer replacement to the conventional coatings.

Influence of Potting Radius on the Structural Performance and Failure Mechanism of Inserts in Sandwich Structures

In this study, the mechanical performance and failure modes of cold-potted inserts within sandwich structures were examined, focusing on the influence of the potting radius, while maintaining constant insert radius and specimen characteristics. In this research, destructive testing was used to evaluate the pull out, load-carrying capacity, and failure mechanisms of the inserts. The methods of stiffness degradation and acoustic emissions (AE) were employed for structural health monitoring to capture real-time data on failure progression, including core buckling, core rupture, and skin delamination. The results indicated that increasing the potting radius significantly altered the failure modes and critical failure load of the insert system. A critical potting radius was identified where maximum stiffness was achieved. Beyond this point, insert fracture became the dominant failure mode, with minimal damage to the surrounding core and CFRP skins. Larger potting radii also led to reduced displacement at failure, increased ultimate loads, and elevated stiffness, which were maintained until sudden structural failure. Through detailed isolation and observation of each failure event and with the use of AE data, precise identification of system damage in real time was allowed, offering insights into the progression and causes of failure.

Effects of openings on postbuckling behavior of large‐size composite C‐beam under bending‐shear coupling load

AbstractProper design and accurate mechanical assessment of composite C‐beam after opening are of great importance in structure engineering. This paper aims to experimentally and analytically investigate the postbuckling response of large‐size C‐beam with web opening under bending‐shear coupling load. New specimen with four different open shapes were designed and tested. Strain gauges and displacement measurements were applied to monitor its buckling behavior, strain field distribution and critical failure load. Four specimens with various openings were loaded until catastrophic failure occurred. Additionally, an analytical model was introduced to predict the residual strength of circular opening. The results indicate that while the presence of an opening significantly decreases the load carrying capacity, it has minimal effect on the bending stiffness. Compared with intact specimen, the initial delamination, buckling and ultimate strength of the circular opening decreases less than those of the rectangular opening. By altering the position of the rectangular opening, improvements can be made in terms of initial delamination resistance and buckling load; however, ultimate strength remains largely unaffected. Reinforcing the edge of an opening further reduces resistance to initial delamination but other two indicators are improved. Overall, from buckling to failure stages, post‐buckling bearing capacity after opening decreases by 40%. Moreover, the shear failure mode is observed during catastrophic failures. And the analysis method employed is relatively conservative.Highlights Ten large size composite C beams are conducted under coupling loads. Deformation, strain distribution and failure mode are presented. Influence of openings on postbuckling behavior of beam is analyzed. An analysis method is employed to predict the residual strength of beam. It could provide valuable insights for assisting in designing beam openings.

Evaluation of mode-I delamination toughness of composites for automotive applications

Abstract With the increasing need for energy efficiency, fiber-reinforced composites are being widely used in the automotive industry. This study investigates the inter-laminar fracture behavior of fiber-reinforced composite double cantilever beam specimens considering a non-zero slope at the root. Experiments were conducted on unidirectional and cross-ply glass fiber reinforced epoxy composite specimens and the critical delamination toughness G I C has been evaluated by the proposed weighted residual equation. The proposed mathematical model requires crack length and the load versus displacement data to evaluate delamination fracture energy. This method accounts the measurement scatter and the rotation at the crack tip. For a particular specimen, the proposed model gives a unique value of critical delamination toughness value. The critical interface failure load estimates utilizing the evaluated delamination toughness agrees well with literature and in-house test results of double cantilever beam specimens.

Fabrication and failure mechanisms of ultralight all-CFRP sandwich cylinders under axial compression

Ultralight all-CFRP honeycomb sandwich cylinders were fabricated using a stretching process. Subsequently, critical failure loads corresponding to five typical failure modes of the sandwich cylinders under axial compression were obtained through theoretical derivation. Three-dimensional failure mechanism maps were generated, which intuitively revealed the influence of the dimensionless parameters on structural failure. The panel thickness was selected as a variable, and quasi-static axial compressive tests were performed on the sandwich cylinders. Two failure modes, intracellular buckling and face crushing, were observed, which is consistent with theory. The experimental results were analysed and discussed systematically. The ultralight all-CFRP honeycomb sandwich cylinders were compared with existing cylinders to reveal their bearing advantages. The established failure mechanism maps provide guidance for the preparation and optimisation of honeycomb sandwich cylinders. Compared with the traditional fabrication processes of honeycomb cores, the novel stretching process is expected to achieve mass production, which is helpful to provide technical support for the lightweight manufacturing of aerospace structural components.

Failures of geometrically asymmetric steel-UHPC composite beams

Geometrically asymmetric steel-ultra-high performance concrete (UHPC) composite structures (SUCSs) suffer several typical failure modes during applications in structural engineering. But the competing mechanism of these failure modes remains a challenge to be urgently overcome. In the present paper, the failure modes of the geometrically asymmetric SUCSs under lateral loads are theoretically predicted and numerically studied. Considering both the geometric asymmetry of the structure and the tensile-compressive asymmetry of UHPC, a theoretical model is proposed to predict the critical failure load for each failure mode (e.g., bending and core shear), and then a failure mechanism map is constructed by comparing each critical failure load. The theoretical predictions are in line with the present numerical results and the previous experimental measurements. The results demonstrate that geometric asymmetry, together with some other geometric parameters and material properties, have remarkable influences on the failure modes of structures. This work provides an effective approach for predicting and designing the failure modes of geometrically asymmetric SUCSs in structural engineering applications, such as undersea tunnels, offshore platforms, and nuclear shielding walls.

Failure predictions for steel-UHPC-steel sandwich beams under three-point bending

In developing a steel-ultra-high performance concrete (UHPC) -steel sandwich structure (SUSSS) for some emerging applications, attention inevitably falls on the failure of the structure. Some typical failure modes have been summarized based on the experimental observations and numerical results. But the prediction of the failure mode is still a challenge. In the present paper, the failure of SUSSSs under three-point bending is investigated theoretically and numerically. A theoretical model is developed to predict the critical failure load of each failure mode on considering the tension–compression asymmetry of UHPC, and a failure mechanism map is constructed to predict the failure mode. The theoretical predictions are validated by the present numerical results as well as the previous experimental results. Based on the theoretical model, the effects of some geometrical and material parameters on the failure modes are discussed. It is demonstrated that the geometries of the SUSSS and the tensile strength of the UHPC core have remarkable effects on the failure modes of the structure. The present work provides a valid method to predict the failure modes of the SUSSSs.

Damage boundary spectrum of pelvis-lumbar spine of seated human under vertical wide-band shock environment

The assessment methods of personnel damage under real shock environments are still an issue. In this paper, a damage boundary for vibration-impact injury in a wide range of frequency domain based on pseudo-velocity shock spectrum (PVSRS) is first proposed with numerical simulation. A high-fidelity three-dimensional finite element (FE) model of pelvis-lumbar spine (P-LS) that the vulnerable organs of seated human under vertical impact conditions, was developed and validated. The random and complex impact loads in real environments were simplified to a series of sinusoidal accelerations with a single frequency and within one period, next loading those equivalent loads on P-LS FE model in vertical direction for batch computing. The results indicated that there is a certain critical failure load that can cause initial damage to P-LS for a specific single frequency. The injury patterns of P-LS show significant frequency sensitivity. The P-LS damage boundary can be obtained from the envelope curve of critical failure loads in PVSRS, which is a V-shaped curve and the frequency corresponding to the trough (18 Hz) is the first natural frequency of the coupled P-LS structures. The asymptote lines of damage boundary are highly consistent with that of theoretical results. The damage boundaries after classifying and standardizing, which rationality in wideband is verified by underwater explosion test data, show more comprehensive and advanced potentials for engineering application.

Deposition and process parameter optimization of electroless Ni-B coating from a stabilizer free bath to achieve enhanced microhardness, scratch-hardness and adhesion using taguchi’s methodology

Electroless nickel boron coatings have wide industrial usage. However, they are generally obtained from a lead-stabilized bath. The present work investigates and optimizes the scratch-hardness and microhardness obtained from stabilizer-free electroless nickel boron bath in a quest to eliminate lead nitrate/heavy metals, which are potentially toxic. The bath temperature, heat treatment temperature, and duration were varied at three levels. Enhanced scratch-hardness (12.581 GPa) was obtained at 85 °C bath temperature and heat treatment at 350 °C for 1 h. At the same time, the highest microhardness (886.17 HV100) was obtained at a parametric combination of 95 °C bath temperature and heat treatment at 450 °C for 1 h. Multi-objective optimization was carried out using grey relational analysis. The parametric combination predicted in multi-objective optimization was 85 °C bath temperature and heat treatment at 350 °C for 1 h where the microhardness was 846.34 HV100. Furthermore, an analysis of variance was also carried out to investigate the importance of the factors in controlling scratch-hardness and microhardness. The highest contribution was observed from heat treatment duration. Further investigation of the optimized coating was done by the progressive scratch test, which recorded that the first critical load of failure improved compared to non-heat treated electroless Ni-B coatings. The coatings were also characterized using field emission scanning electron microscope, energy dispersive x-ray spectroscopy, and x-ray diffraction. The coatings in optimized condition showed no transverse or chevron cracks within 5–24 N.

Improving the adhesion of CrN coatings on TC4 alloy substrates by discharge current modulation in magnetron sputtering

ABSTRACT The study reports the formation of multilayer coatings of CrN with variable gradient modulus on TC4 substrate by varying the discharge current of the hot filament in magnetron sputtering. Results show that multilayer CrN/TC4 has a higher critical failure load (63.4 N > 29.7 N), lower maximum tensile stress (103.8 GPa < 134.3 GPa), and a higher ratio of plastic to elastic deformation work (Wp/We, 2.11 > 1.58) than a single layer CrN/TC4. This indicates that the energy absorption ability of the coating/substrate before failure can be improved by increasing the loose energy-absorbing sublayer, thus improving the coating/substrate adhesion. Notably, the wear rate of both multilayer and single-layer coatings is in the order of 10−16 m3/(N·m), demonstrating their excellent wear resistance. Structural engineering enables the application of multilayer CrN coatings on low-modulus and high-strength alloy substrates, such as TC4.

A simplified finite element method for failure analysis in adhesive-bonded nozzle diffuser of solid rocket motors

The adhesive bond between the nozzle diffuser shell and the insulation layer of solid rocket motors (SRM) is widely used due to its lightweight, simple design, and easy operation. The mechanism of adhesive-bonded failure between them is a concern for designers. In this paper, a simplified finite element method for failure analysis in the adhesive-bonded nozzle diffuser of SRM is proposed. In the method, the diffuser shell, insulation layer, and adhesive between them are considered elastic. The maximum Von Mises stress failure criterion is assumed to be suitable for the adhesive. The adhesive-bonded failure is simulated by using the user subroutine VUSDFLD in the commercial Finite Element Analysis software ABAQUS. The method is verified to be simple but effective based on the comparison with experimental results. The adhesive-bonded failure process under external load can be well simulated, and the critical external load of adhesive-bonded failure can be accurately predicted. In addition, the method is utilized to study the failure of the nozzle diffuser with several kinds of original debonding. It is suggested that the original axial debonding ratio should be less than 60%, and the circumferential debonding angle should be smaller than 30° in the conical section of the nozzle diffuser.

Energy absorption and collapse behavior of PP‐based pin‐reinforced composite sandwich panels under quasi‐static flatwise compression loading

AbstractThis article investigates the energy absorption and failure behavior of thermoplastic composite sandwich panels made entirely of polypropylene (PP) and pin‐reinforced core under quasi‐static compressive loading. The pins are manufactured by thermoforming and assembled with face sheets. The specimens were subjected to flatwise compressive loading to examine energy absorption capabilities. Moreover, the finite element method (FEM) is used to analyze core sandwich panels reinforced with cubic, cylindrical, beam, and cross‐beam pins. Furthermore, a closed‐form analytical model is adopted and developed to predict the critical load of these structures. The performed experiments were utilized to validate the damage mechanisms and critical displacements of the simulations and the analytically calculated maximum collapse loads. The results demonstrate that the predictions accurately capture both the critical failure load and failure mechanisms. Since the numerical results have a reasonable correlation with the experimental results and their output difference is &lt;15%, FEM is used to investigate the collapse behavior of the pin‐reinforced foam‐filled panels. A comparison of the load–displacement, specific energy absorption (SEA), and maximum collapse loads of the samples shows that the cubic reinforced foam‐core sandwich panel has the maximum peak load and SEA. The FE model of pin‐reinforced foam‐filled panels reveals that the buckling of the reinforcements is postponed to a point beyond the critical one. Hence, PP foam can act as lateral support and delay the ultimate failure in panels, especially pin‐reinforced cylindrical sandwich panels, up to 40%.

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV100 at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV100. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.

Experimental Studies and Numerical Simulations of FRP Poles Failure in the Area of Inspection Hole

Glass fiber-reinforced polymer (GFRP) utility poles are becoming more widespread in European countries. To ensure the integrity and safety of poles, it is necessary to carefully examine their structural features. The purpose of this paper is to present the numerical model of a column made with the engineering simulation software ANSYS and to compare the experimentally determined values of the stresses that lead to column failure close to the inspection hole with the results obtained using the numerical model. The critical buckling and failure loads for GFRP poles, as well as the associated modes of failure, were correctly predicted by the finite element method used in this study. Failure occurred in the middle of the inspection hole's longer edge at a stress level of 220-250 MPa. A comparison of the stress using the ANSYS simulation software that led to the destruction of the column with those measured experimentally using strain gauges revealed a good agreement between their values.

Service Life Prediction of Flexible Concrete Mattresses (FCMs) in the Yangtze River

Many scholars have studied the failure mechanism of waterway regulating structures, but there is still a need to improve research on their reliability and service life in the industry. Currently, flexible concrete mattresses (FCMs) are the regulating structure widely used on the Yangtze River Golden Waterway, so it is important to study their service life. The stability function has been built based on the mechanism of stability against sliding and a time-varying reliability model. Experiments have been conducted to analyze the critical failure load of FCMs, determine the influence parameters, and derive a service life calculation formula. Finally, the middle reaches of the Yangtze River were taken as an example for analysis.

Three-dimensional exact solutions of double-coated structure with arbitrary thickness under normal point load

Explicit closed expressions of stresses and displacements of an adherend and an adhesive provide researchers and designers with insight into the effects of variable parameter properties on structural performance. Through potential theory method, the Green's functions of a double-coated structure under normal point load are solved using the mirror image method, where the mirror image rule satisfies the recursion law of the Fibonacci sequence. The stress distribution of the multilayer structure under the action of point load is presented in the form of an infinite series with a fast convergence rate. A guideline for the design of coating thickness and material parameters to reduce interfacial stress is developed (reduce adhesive thickness, reduce elastic modulus of adherend, increase elastic modulus of adhesive). The accuracy of the exact solution is demonstrated through comparison with contact analytical solutions. In addition, the critical load of interface shear delamination failure is predicted. The stresses and displacements of the adherend and the adhesive are presented with the solutions, which can serve as a reference for researchers and designers.

Multiobjective design optimization of double arrowhead auxetic model using Lichtenberg algorithm based on metamodelling

In this paper, five parameters of a double arrowhead auxetic model were analyzed: mass, critical buckling load, natural frequency, Poisson’s ratio, and maximum load of compression. A Response Surface Methodology was considered and applied together with a new meta-heuristic of optimization called the Multi-Objective Lichtenberg Algorithm to optimize the structural performance of the auxetic model. All the results were obtained from numerical solutions that were validated with experimental tests. The optimization analysis was able to increase the critical buckling and failure load by 3.4% and 4.8%, respectively, in compression performance. In modal performance, it was possible to increase the natural frequency by 26.88% and reduce the Poisson’s ratio by 24.59%. This is a study unprecedented in the literature to date because numerical, experimental, and statistical analysis were done to understand the behavior of the double arrowhead auxetic model in a multi-objective optimization problem.

The failure behavior of double-layer metal foam sandwich beams under three-point bending

The failure behavior of the double-layer metal foam sandwich beam under three-point bending is investigated experimentally and analytically. Three main failure modes are observed, i.e. indentation, face yield and core shear A-AB. Also, the combined indentation and face yield, and core shear and indentation are observed, respectively. The analytical formulas are given to predict the critical failure loads of double-layer sandwich beams under different failure modes. Analytical results are in good agreement with the experimental ones. The failure mechanism maps of double-layer sandwich beams are constructed, and the minimum mass design of the double-layer metal foam sandwich beam is presented.

Simulating hydrogen embrittlement fracture based on phase field method

The phase field hydrogen embrittlement fracture model is improved by introducing tension-compression split of strain energy. The numerical formulas of the model are provided, besides, the coupling term of concentration field and displacement field is deduced. The matlab software is used to compile the numerical program of phase field hydrogen embrittlement fracture. The modes I and II cracks of hydrogen embrittlement are simulated respectively. The simulation results show that hydrogen ions concentrate at the crack tip where stress concentration happens, and that the hydrogen concentration reduces the critical failure load of the square plate. Compared with the numerical results of the existing models, the improved model can accurately calculate the critical failure load in the mode I crack and capture the embrittlement fracture phenomenon when the phase field and the concentration field are accumulated near the crack tip. Moreover, the improved model can effectively simulate the mode II crack with hydrogen embrittlement.

The failure behavior of buckling pin valve: Theoretical, numerical, and experimental study

At present, buckling pin in the bypass of piping as pressure relief valve has been gradually utilized in the low-concentration coal-bed methane (CBM), which bends to release pressure when the main valve fails leading to pipeline blockage. However, current researches mainly focused on the buckling behavior of hydraulic cylinder rod or rod string, and less consideration was given to the operational reliability of buckling pin valves. This paper deduced the calculation formula of the critical failure load based on Euler formula in the buckling pin under buckling load. Besides, three finite element models (FEM) based on Johnson−Cook constitutive model were compared to predict failure strength of buckling pin which were verified by experiment. In addition, the defect sensitivity analysis of the buckling pin under different initial geometric defects rate was carried out. The results showed that a) the experimental value of the critical failure load in the buckling pin was 206.04 N and the bending position was in the middle of the buckling pin; b) the analysis result adopting explicit dynamic method was in best agreement with the experimental results within deviation of 0.24%; and c) the initial geometric defect of buckling pin should be controlled within 1%. This study provides an important reference to predict the critical failure load of the buckling pin valve and achieve safe transportation of low-concentration CBM.