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A high‐temperature multi‐axial test is carried out to characterize the thermo‐mechanical behaviour of a 3D‐woven SiC/SiC composite aeronautical part under loads representative of operating conditions. The sample is L‐shaped and cut out from the part. It is subjected to severe thermal gradients and a superimposed mechanical load that progressively increases up to the first damage. The sample shape and its associated microstructure, the heterogeneity of the stress field and the limited accessibility to regions susceptible to damage require non‐contact imaging modalities. An in situ experiment, conducted with a dedicated testing machine at the SOLEIL synchrotron facility, provides the sample microstructure from computed micro‐tomographic imaging and thermal loads from infrared thermography. Experimental constraints lead to non‐ideal acquisition conditions for both measurement modalities. This article details the procedure of correcting artefacts to use the volumes for quantitative exploitation (i.e. full‐field measurement, model validation and identification). After proper processing, despite its complexity, the in situ experiment provides high‐quality data about a part under realistic operating conditions. The influence of the mesostructure on fracture phenomena can be inferred from the tomography in the damaged state. Experiments show that the localization of damage initiation is driven by the geometry, while the woven structure moderates the crack propagation. This study widens the scope of in situ thermo‐mechanical experiments to more complex loading states, closer to in‐service conditions. An in situ corner bending test under a high thermal gradient is followed by both computed tomography and thermography. Experimental procedure, image processing and preliminary conclusion are presented.

The effects of elevated temperatures on the performance of glass-reinforced epoxy (GRE) pipes under multi-axial loadings were investigated. Finite element software was used to develop the layers of the winding angle on GRE composite pipes. The simulations of the closed-ended pipes’ performance under internal pressure loadings of various hoop to axial stress interactions were observed, then the failure strength was illustrated in the form of a failure envelope. Five different stress ratios ranging from pure axial loading 0:1, 1:1, 2:1, 4:1 and pure hoop 1:0 were tested at elevated temperatures (room temperature (RT), 65°C and 95°C) respectively. The first ply failure (FPF) for GRE pipes was predicted based on Tsai–Wu failure criteria. The results show that the highest temperature reduced the strength of the GRE pipes since the hoop and axial stress decreased with increasing temperature and thus the mechanical properties of the GRE pipes were degraded with the increase of temperature. Both showed a strong dependence on the stress ratio and test temperatures. Moreover, as the temperature increases, the glass fibres become more ductile and cause the failure envelopes to shrink towards the origin and become slightly narrower to accommodate the increase in strength of the composite pipes. It is shown that the initial failure stress based failure envelope at elevated temperatures generally degraded, except for the 2:1 loading where the initial failure stress increased.

Predicting a component’s fatigue life requires information on not only the number of stress cycles the component will undergo but also the kind and frequency of those stress cycles, as well as information about the surrounding environment and the intended purpose of the component. Models that can forecast lifespan by utilizing available experimental data are preferred since fatigue investigations are costly and time-consuming. Therefore, this work focuses on fatigue testing of S355 mild steel specimens under multiaxial loading conditions involving bending and torsion. The impact of phase-shifted loading conditions on material behavior, considering in-phase and with angles 0°, 45°, and 90°, has been studied. Then, the data of fatigue tests involve variations in loading amplitudes, and configurations used in different ML algorithms such as lazy k-nearest neighbors (Lazy-KNN), linear regression (LR), and random forest (RF) were employed for predictive modeling. These models are evaluated based on their ability to predict nominal stresses, torsion, and bending moments under varying loading configurations. The predictive modeling results are visually presented, showcasing the effectiveness of Lazy-KNN in accurately predicting material responses. Quantitative analyses further confirm the robustness of Lazy-KNN in predicting bending, nominal stress, and torsion under different loading conditions. The study provides valuable insights into the fatigue behavior of S355 mild steel and highlights the significance of considering multiaxial loading configurations in material testing and design.

Hydraulic structures are typically subjected to long-term hydraulic loading, and concrete—the main material of structures—may suffer from cracking damage and seepage failure, which can threaten the safety of hydraulic structures. In order to assess the safety of hydraulic concrete structures and realize the accurate analysis of the whole failure process of hydraulic concrete structures under the coupling effect of seepage and stress, it is vital to comprehend the variation law of concrete permeability coefficients under complex stress states. In this paper, several concrete samples were prepared, designed for loading conditions of confining pressures and seepage pressures in the first stage, and axial pressures in the later stage, to carry out the permeability experiment of concrete materials under multi-axial loading, followed by the relationships between the permeability coefficients and axial strain, and the confining and seepage pressures were revealed accordingly. In addition, during the application of axial pressure, the whole process of seepage–stress coupling was divided into four stages, describing the permeability variation law of each stage and analyzing the causes of its formation. The exponential relationship between the permeability coefficient and volume strain was established, which can serve as a scientific basis for the determination of permeability coefficients in the analysis of the whole failure process of concrete seepage–stress coupling. Finally, this relationship formula was applied to numerical simulation to verify the applicability of the above experimental results in the numerical simulation analysis of concrete seepage–stress coupling.

The main purpose of this study comprises the design and the development of a novel experimental configuration for carrying out tests on a full-scale stiffened panel manufactured of fiber-reinforced thermoplastic material. Two different test-bench design concepts were evaluated through a numerical modeling strategy, which will be validated at the next stage using a targeted series of mechanical tests. A baseline experimental setup was developed after a number of candidate configurations were numerically investigated. The supporting elements along with the load introduction systems were defined in such a way as to represent the stiffness of a fuselage barrel section and its representative loading scenarios. The test rig and the investigated thermoplastic panel were numerically simulated to acquire valuable data pertaining to deformations and stresses when subjected to different loading combinations. Two distinct load cases were numerically examined: the first case was the in-plane compression of the thermoplastic panel, while the second case consisted of an internally applied pressure load introduced via an inflatable airbag, installed under the panel. Both loading scenarios were recreated inside the numerical virtual environment in order to examine two distinct stiffening configurations as well as to determine the maximum/limit loads to be used in the planned future experimental campaign. It was concluded that the designed test rig could successfully be used for the structural evaluation of fuselage panels under representative loading conditions.

The subject of the present work is the development and implementation of a novel testing facility to carry out an experimental campaign on an advanced fuselage panel manufactured from both thermoplastic and metallic materials, as well as the validation of its numerical simulation. The experimental arrangement was specifically designed, assembled, and instrumented to have multi-axial loading capabilities. The investigated load cases comprised uniaxial in-plane compression, lateral distributed pressure, and their combination. The introduction of pressure was enabled by inflatable airbags, and compression was applied up to the onset of local skin buckling. Calibration of the load introduction and inspection equipment was performed in multiple steps to acquire accurate and representative measurements. Data were recorded by external sensors mounted on a hydraulic actuator and an optical Digital Image Correlation (DIC) system. A numerical simulation of the fuselage panel and the test rig was developed, and a validation study was conducted. In the Finite Element (FE) model, several of the experimental configuration’s supporting elements and their connections to the specimen were integrated as constraints and boundary conditions. Data procured from the tests were correlated to the simulation’s predictions, presenting low errors in most displacement/strain distributions. The results show that the proposed test rig concept is suitable for stiffened panel level testing and could be used for future studies on similar aeronautical components.

Foundation piles can be used as a means for increasing the capacity of the foundations under static loads or, at the same time, can be regarded as an additional source of energy dissipation for the structure during strong motion. Under multi-axial loading, the ultimate capacity of a pile group is closely connected with the attainment of the flexural strength in the piles, which can in turn vary significantly according to the specific load path followed. Nonetheless, the design of piled foundations is still based on an independent evaluation of the vertical and horizontal capacities without accounting for the interaction between the several loads acting on the footing. To overcome this issue, in this paper a simplified numerical procedure for evaluating the capacity of piled foundations under multi-axial loading conditions is developed, which is based on the lower bound theorem of plastic limit analysis. On the basis of the numerical results, an analytical model of ultimate limit state surface is proposed, representing the force combinations that activate global plastic mechanisms of the soil–piles system. The identification of the ultimate surface necessitates a limited number of parameters having a clear physical meaning. The ultimate surface can lead to an optimised design of pile groups, allowing for a better control of the ultimate capacity as a function of the expected load patterns under static and dynamic conditions. In structural analysis, the ultimate surface can also be regarded as a bounding surface of a plasticity-based macroelement for piled foundations to account for the nonlinear features of the soil–pile system.

Modeling the mechanics of human vocal folds during phonation is a challenging task. This is partly due to the mechanics of their soft and highly anisotropic fibrous tissues, which undergoes finite strains with both elasticity and strain-rate sensitivity. We propose a visco-hyperelastic micro-mechanical model capable of predicting the complex cyclic response of the vocal-fold fibrous tissues based on their histo-mechanical properties. For that purpose, we start from the hyperelastic micro-mechanical model proposed by Terzolo et al., 128:105118 (2022). We include in the model non-linear viscoelastic contributions at the fibril scale to account for the dissipative and time-dependent response of vocal-fold tissues. The relevance of the model is demonstrated and discussed through comparison with a comprehensive set of reference experimental data, within a wide range of loading modes, strains, and strain rates: cyclic and multi-axial loadings at finite strains (tension, compression and shear), along with small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) from low to high frequencies. This study elucidates how the viscoelasticity of vocal-fold tissues can result from combined time-dependent micro-mechanisms, such as the kinematics and the deformation of their fibril bundles, along with the mechanical interactions likely to develop among fibrils and the surrounding amorphous matrix.

This study investigated the type of failure modes of different cross-arm designs under multi-axial static loading. The failure modes were numerically predicted from real-scale finite-element models of cross-arm integrated with a Hashin damage subroutine. Three finite-element models of cross-arm were considered; a model with standard cross-arm design, a standard design engaged with braces, and a standard design engaged with sleeves. The failure analysis of the composite cross-arm was focused on the location and type of failure of the structure upon its application. This investigation revealed that under the applied load, the cross-arm with installed sleeves exhibited the lowest total deflection of 0.21 m. Every cross-arm design exhibited fiber failure due to the tension and compression mode, regardless of the support system installed. Additionally, the installation of sleeves and braces on the cross-arm structure successfully reduced the number of areas associated to failure.

The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also, an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can be estimated through Dirlik’s method with probability density function. The work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison was performed for a simple cantilever beam exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).