International Journal of Solids and Structures最新文献

The characterization of the mechanical properties of soft films is of great importance for their applications. In our previous research, we demonstrate the existence of a maximum load occurring during the indentation process of a perforated film by a spherical indenter. Based on this result, an approach to obtain the shear modulus of the film material using the method of finite element analysis has been proposed. However, our previous work does not consider the effect of friction between the film and the indenter, which has a significant influence on the value of the maximum load. Here, a theoretical model is presented which takes into account the role of friction. The reliability and accuracy of the theoretical model are validated by comparison with simulations and experimental results. In addition, the indenter eccentricity and round hole shape deviations which commonly occur in actual indentation tests, are investigated by combining indentation test measurements with finite element analysis. The performance of this method on porous films is also analyzed experimentally and numerically. The results reveal that this indentation method is still effective for porous films. This work provides a fundamental understanding of the mechanism of the indentation method and is expected to provide a new perspective for local characterization of films, even with multiple holes.

Harmonic holes are designed to leave the mean stress as a constant in the surrounding material. When surface tension is imposed on the boundary of the holes, the existence of harmonic holes within an infinite elastic plane subjected to plane deformation was verified roughly in the literature by numerical techniques. However, a rigorous proof for the existence of harmonic holes has still been absent in the literature for any of the cases involving surface tension. In this paper, we perform an accurate analysis for the case of a single harmonic hole with constant surface tension in an infinite elastic plane under a uniform remote (in-plane) shear loading. We show that the harmonic hole exists strictly if and only if a certain combination of the surface tension, shear loading and the size of the hole does not exceed a critical value. Explicit exact formulae are obtained for describing the shape of the harmonic hole in both deformed and undeformed configurations. These formulae may find applications in the design of functional porous materials, in validating relevant numerical methods and in elucidating the preferred shapes of fluid-elastic membranes and cell membranes.

During the ship, collisions with reefs or grounding may cause damage to the hull of ships made of sandwich plates. The cutting failure mechanism of sandwich panels is still not fully understood. In this paper, the failure behavior of metal foam sandwich plates under cutting load by a wedge-shaped indenter is studied through analytical, experimental, and numerical methods. An analytical model is proposed to describe the cutting failure behavior of foam core sandwich plates. Based on experimental results, three distinct failure modes of foam sandwich plates with varying thicknesses are observed. Numerical simulations are performed, and analytical and numerical results capture experimental results reasonably. The effects of core thickness, face-sheet thickness, and tip angle and cutting angle of wedge indenter on the failure mode, load-carrying capacity and energy absorption performance of the sandwich plates are explored. The present analytical model can effectively predict the cutting failure behavior of sandwich plates.

We investigate the concurrent three-dimensional (in-plane and out-of-plane) deformations of fiber-reinforced composite (FRC) sheets undergoing lateral pressure. This involves the utilization of the Neo-Hookean strain energy model for the matrix material and computing the strain energy of bidirectional fibers by accounting for the stretching, bending, and twisting responses of the fibers. The kinematics of FRC are formulated within the framework of differential geometry on FRC surfaces, including the computations of the first and second gradient of deformation. By employing the variational principles, we derive the Euler equations describing the mechanics of the fiber–matrix composite system subjected to lateral pressure. The resulting three-dimensional continuum model theoretically predicts the deformation of the matrix material and it is found that the maximum deformation of matrix material occurs in the diagonal direction of the domain, yet, the center of the domain suffers weak in-plane deformation because of surface tension equilibrium. In addition, the stretching, bending, and twisting kinematics of fiber units are computed to investigate the effects of the individual fiber’s kinematics on the overall deformation of fiber meshwork. Lastly, it is found that the lateral pressure on the FRC surface induces fiber flexure in the vicinity of domain boundaries and fiber stretch inside the domain, corresponding to the intensified shrinking strain near the edges and stretching strain in the middle of the domain. The theoretical results provide phenomenologically meaningful insights into comprehending the damage patterns of the fiber-reinforced building material, the hemispherical dome shaping results of bamboo Poly (lactic) acid (PLA) composites and the out-of-plane deformation of woven fabric.

Nickel (Ni)-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent mechanical properties, and cracks as unavoidable defects may affect the mechanical performances of materials dramatically. In this paper, large scale molecular dynamics (MD) simulations are carried out to understand the deformation mechanisms of Ni-based single crystal with a central crack under tension. Here, the effects of matrixes (γ, γ′ and γ/γ′), strain rates (1 × 10⁹ s⁻¹ ∼ 3 × 10⁹ s⁻¹) and temperatures (300 K∼900 K) on the role of crack propagation are considered. It is observed that dislocations and slip systems in the γ′ model are concentrated near the crack, resulting in the rapid expansion of dislocation, which leads to the fastest crack growth speed and early fracture. While the crack propagation rate of γ and γ/γ′ models are relatively slow, due to the combined action of the Lomer-Cottrell lock and stacking fault tetrahedron structure and Stair-rod dislocation, which hinders crack propagation. In addition, deformation at increased strain rates and/or reduced temperatures, lead to superior yield stress and Young′s modulus for models with a central crack at γ/γ′ interface. On the other hand, high temperature and high strain rate will promote crack propagation in the γ phase, and the higher the strain rate and/or temperature, the faster the crack propagation speed will be. These results will enrich our understanding on the crack propagation and evolution mechanisms in Ni-based single crystal superalloy.

For screw dislocations in BCC metals, three mysteries have persisted, that is, compact vs degenerate core structure, single-hump vs double-hump Peierls barrier, and the relation between the core structure and Peierls barrier. We discover that the compact core consists of atoms in a FCC stacking sequence and that the degenerate core consists of atoms in a HCP stacking sequence, suggesting that BCC, FCC, and HCP must be considered to correctly capture the core structure. Informed by a machine learning model, we can generate interatomic potentials that reliably predict a compact core structure. We further show the compact core structure does not necessarily lead to the single-hump Peierls barrier.

In this study, three novel multi-directional energy-absorbing honeycombs were designed to meet the requirements in the crash of uncertain directions, which are named as bow-shaped honeycomb (BSHC), staggered honeycomb (SGHC) and corrugated honeycomb (CGHC). These innovative designs can significantly narrow the huge gap of the energy absorption capacity between the in-plane and out-of-plane directions of traditional honeycombs. Compression tests were conducted in three orthogonal directions. The BSHC is found to have the smallest densification strain but the highest plateau stress in each direction. The SGHC can only balance the energy absorption between out-of-plane and in-plane-x directions. The CGHC demonstrates a better densification strain and the highest multi-directional energy absorption coefficient. The detailed and equivalent finite element models of CGHC were further established and validated, and both exhibited high accuracy. Finally, a honeycomb anti-climber, with only about half length of the traditional guided honeycomb anti-climber, was designed and equipped with metro vehicles. Simulations were conducted under eccentric collision scenario. The results demonstrated that the CGHC anti-climber was capable of orderly deformation in the axial direction (out-of-plane direction) while effectively resisting the vertical (in-plane-y direction) force during collision. The energy absorption capacity of CGHC anti-climber was significantly enhanced as compared to the HEHC anti-climber under eccentric collision scenario.

The complex shape of the structure and the new needs for high-precision in digital twin modeling pose challenges for sensor placement optimization. A novel optimal sensor placement towards the high-precision digital twin (OSP-HDT) method is proposed for complex curved structures. It comprises three key aspects. Firstly, leveraging the spatial dimensionality reduction method, the complex curved surface is simplified into a planar representation. Subsequently, candidate sensor placement points can be easily identified by dividing the background mesh in the plane and screening them within the curved surface. These candidate points are then binary encoded to facilitate the subsequent optimization. Secondly, the method collects result data from the finite element model, treating it as virtual sensor data. Using this data, a surrogate model is constructed and then the objective function is formulated based on both the global and local critical areas precision of the surrogate model. Thirdly, the sensor placement optimization model is constructed, followed by optimization design using the efficient multi-objective covariance matrix adaptive evolutionary strategy. Through the steps above, the optimal sensor placement can be identified. To validate the proposed OSP-HDT method, an experiment is conducted on an S-shaped variable cross-section stiffened shell, with the construction of the corresponding digital twin. Compared to the uniform placement with an equivalent number of sensors, the OSP-HDT method demonstrated a significant 9.0% improvement in global precision and a remarkable 62.1% enhancement in local precision of critical areas. Furthermore, when compared to the random sensor placement strategies, the OSP-HDT method exhibited a 20.5% increase in global precision, together with a 44.2% increase in the local precision. Notably, even when compared to the full sensor placement, the OSP-HDT method can maintain comparable local precision, while significantly reducing the number of sensors by 77.6%. The above comparison indicates that the proposed OSP-HDT method can build a digital twin model with higher global and local precision for complex structures.

The present study aims to describe the in-plane differential hardening behaviour of the twinning induced plasticity sheet metal TWIP980 under various stress states, including uniaxial tension, plane strain tension, and pure shear, particularly focusing on non-proportional loading conditions. The true stress–strain curves for each stress states were inversely obtained from their corresponding load–displacement curves and modeled using a differential hardening model that can accommodate all three stress states simultaneously on plastic work (density) contours. For non-proportional loading tests, oversize specimens were initially stretched under uniaxial tension up to a 10% pre-strain along the rolling, diagonal, and transverse directions, respectively. Subsequently, the three stress states were applied to subsize specimens cut from the deformed oversize specimens along the rolling direction. To describe the hardening behaviours during non-proportional loading, a homogeneous anisotropic hardening model was adopted and calibrated using two-step uniaxial tension tests. Subsequently, the differential hardening model was successfully incorporated into the homogeneous anisotropic hardening model to describe both the differential hardening and the strain path change-induced hardening behaviours under the two-step loadings, i.e., uniaxial tension to pure shear and uniaxial tension to plane strain tension. Both experimental and simulation results underscore the necessity to consider differential hardening under non-proportional loading conditions.

Reinforced thermoplastic composites (RTPC) exhibit weak interfacial strength due to the low surface energy of the polymer matrix. Recently, a concept of controlled mechanical interlocking was introduced that showed significant improvement in the interfacial shear strength with pure mechanical interlocking and no chemical bond/friction. In this paper, a parametrized continuum material model is developed through computational homogenization for an E-glass/polypropylene (PP) composite system with a mechanically interlocked interface. Such parametric models not only elucidate the effects of the microstructural parameters on the mechanical behavior of the material but also enables the optimization of the composite at the microstructure level.