Composite Structures最新文献

Mixed mode delamination is prone to occur in composite laminates subjected to complicated loading. In current study, the modified maximum principal stress (M-MPS) criterion and the modified maximum shear stress (M-MSS) criterion considering the effect of mode ratio on the critical distance are developed to predict the mixed mode delamination of unidirectional laminates. The accuracy of the proposed fracture criteria is validated by the comparison of the predicted fracture locus curve with extensive experimental data available in the literatures, a higher correlation is observed between the predicted results and the experimental data. Finally, comprehensive discussion on the capability of the proposed M-MPS and M-MSS criteria is conducted, a dimensionless parameter named fracture index composed of the difference of elastic properties and the difference of pure mode fracture toughness is proposed to reveal the fracture mechanisms of the unidirectional composites.

Variable stiffness composite structures show great application potential due to their flexible spatial stiffness adjustment ability. In this paper, the accurate and efficient dynamic models of variable stiffness composite cylindrical shells considering the effects of the flange are established based on a semi-analytic frame. Then, the finite element models of the corresponding structures are established by using the ANSYS commercial software. Through the comparison of the calculation results between models under two analytical frameworks, the correctness and efficiency of the proposed modeling method are well verified and reflected. In addition, an instant hammering test of a composite cylindrical shell with flange is carried out to verify the accuracy of the modeling method at the experimental level. Then, the influence of design parameters on frequency trajectories and modals of the variable stiffness composite cylindrical shell with flange is studied. The analysis results show rich and interesting phenomena, among which, the circumferential variable stiffness composite cylindrical shell with and without flange exhibits complex frequency veering behavior under continuous variations of design parameters. The research work has a certain guiding significance for the dynamic optimization design of the variable stiffness composite cylindrical shell with flange.

Vibration control plays a vital role in engineering structures, especially for low-frequency range, because designing structures with small dimensions makes it difficult to control large-wavelength vibrations. The present study seeks another road to realize low-frequency vibration control from the view of the real vibration responses. Similar to mode shapes, deflection modes are the main distributions of vibration amplitudes on structures in low frequency. Therefore, they are also essential vibration characteristics of structures. This paper proposes an effective passive vibration control method under both non-resonant and resonant excitations based on deflection mode theory and optimal algorithm. In fact, it is just like an axially functionally graded design for structures. The equations of motion for non-uniform beam structures are formulated by Hamilton’s principle. Firstly, a desired deflection mode is artificially designed, and the beam structure is discretely divided into subunits. Then, by adjusting the thickness or elastic modulus of each subunit to make the deflection mode of the beam coincide with that of the desired one. This process is completed by the genetic algorithm (GA). After that, by experimental and simulation analyses, the deflection mode of the optimally designed beam structures coincides with that of the desired one. Therefore, the present vibration control method is verified to be correct and effective.

In this paper the static behaviour of polyphenylenesulfide reinforced by 40% wt. short glass fibre net-shaped plain and notched specimens was investigated. The specimen geometries were obtained by injection moulding and the experimental results were compared with data obtained from machined specimens with the same material and geometries. All data were reanalysed according to several models available in the literature for orthotropic materials, to find a rapid and efficient assessment tool for predicting the strength of short glass fibre reinforced materials in the early design stages. To this end, approaches based on orthotropic linear elastic stress analysis were considered, namely the linear elastic peak stress criterion, the nominal net-stress criterion, the point stress criterion, the average stress criterion, the strain energy density criterion, the generalized stress intensity factor-based approach, the inherent flaw model, the damaged zone criterion and the Hitchen criterion. Among the models, the average stress criterion and the generalized stress intensity factor-based approach provided the most accurate predictions of the static strength, ranging from −10% to +9% and from −19% to +2%, respectively, compared to the experimental data.

Composite laminated thin-walled structures, widely used in high-speed aircrafts, undergo a complex thermal–mechanical coupling environment. Geometrical nonlinearities with a thermal effect bring significant challenge to finite element analysis of structures. In this paper, a novel hybrid-stress method based on the solid-shell element is proposed for nonlinear thermoelastic analysis. An eight-node solid-shell element (CSSH8) is developed based on the assumed natural strain method and hybrid-stress formulations to overcome various locking problems and achieve an effective 3D simulation for structures with a large span-thickness ratio. The Green–Lagrange displacement-strain relation is selected to take the geometrical nonlinearities into account. The modified generalized laminate constitutive model is extended to consider both the thermal expansion and temperature-dependent material properties. A temperature variation along the laminate thickness can also be assumed in the constitutive model. Nonlinear thermoelastic equilibrium equations are derived using the Hellinger–Reissner variational principle, in which five different coupling cases for thermal–mechanical loads can be fully involved. Numerical examples demonstrate that the proposed method with CSSH8 element is insensitive to various distorted meshes and numerically robust to pass the buckling point; meanwhile large step sizes can be achieved in the path-following nonlinear thermoelastic analysis.

As the rapid developing in infrared detection technology, infrared camouflage has attracted increasing attention in militarily. The two-dimensional transition metal carbide/nitride (MXene)-based film have been developed in IR stealth due to the low IR emissivity. However, the adjusting thermal camouflage is still a great challenge. In this study, we successfully fabricated a sandwich-structured MXene-ANF-MXene nanocomposite film by the vacuum-assisted filtration process. The composite film displayed remarkable infrared stealth performance of large reduction in radiation temperature. The lowest IR emissivity was 0.21. Additionally, adjusting infrared disguise and temperature modulation of the film were achieved by a stable and reliable Joule heating capability. The resulting composite film also exhibited multifunctionality including an impressively high electromagneticinterference(EMI) shielding efficiency of up to 56.2 dB, excellent mechanical properties, flame retardancy, and hydrophobicity. This work offers a simple avenue for preparing multifunctional sandwich-structured composite film by vacuum-assisted filtration method, demonstrating the great promise of MXene film for multifunctional application.

Poly methyl-methacrylate (PMMA) is one of the most widely used polymer composite materials in orthopaedic and trauma surgery. However, this material can change its mechanical properties when exposed to the highly aggressive environment of the human body, which may result in joint implant loosening and thus in a need for revision surgery. Therefore, in recent years, numerous researchers have investigated the effect of adding various particles to PMMA in order to obtain a composite bone cement with enhanced mechanical properties. In our study, we examined the effect of adding different grain sizes of hydroxyapatite (HA) to the commercially available PMMA (Palamed, Heraeus) on the mechanical properties of the fabricated PMMA/HA bone cement composite. Samples were subjected to compressive loading, as this type of load reflects typical conditions in the human body after joint prosthesis implantation. Hydroxyapatite of two different grain sizes was used: 5 µm (HA5) and 10 µm (HA10). Being a naturally occurring bone mineral, hydroxyapatite can improve the biocompatibility of bone cements, which would prolong the total joint replacement (TJR) survival rate. However, when added to PMMA, HA can affect its mechanical properties. In this study, the effects of adding HA was added in 0, 1, 2, 3, 5, 8, 10 % of dry mass were analysed. Obtained results demonstrated that only the addition of 2 % HA had a significant impact on the mechanical properties of PMMA. The other percentage concentrations had no effect on PMMA properties.

Perforation in cylindrical shells is commonly a typical technique to fulfill relevant functional requirements. However, how the perforation influence the mechanical performance of thermoplastic composite cylindrical shells (TPCCS) is incompletely understood. Hence, a systematic investigation through quasi-static compression and low-velocity impact (LVI) experiments was carried out in this paper. The full-field strain distributions of TPCCS intact tubes (IT) and perforated tubes (PT) were monitored by using 3D-DIC, and the residual properties were also characterized by compression-after-impact (CAI) tests. The results show that under quasi-static compression, the structural stiffness decreases significantly with increasing perforation diameter. The perforation reduces the interference of internal random defects on the structural deformation mode, which leads to a significant strain concentration in PT. The peak force and initial stiffness under LVI are smaller than those under quasi-static compression, with IT displaying higher sensitivity to dynamic loading compared to PT. At the impact energy of 100 J, IT and PT exhibit “S”- and “X”-shaped deformation modes, respectively. CAI tests indicate that although PT has a poorer residual load-carrying capacity than IT, it retains good structural integrity and secondary energy absorption capacity. This study provides a valuable reference for the assessment and application of perforated TPCCS.

Bone cements based on poly methyl-methacrylate (PMMA) are among the most widely used polymer composites in orthopaedic surgery. They play a key role in fixing the endoprosthesis with the bone, and, as such, are the weakest link in total joint replacement (TJR) surgeries. A fast, premature decrease in the mechanical properties of PMMA in an aggressive environment, such as the human body, can lead to TJR loosening, which results in the necessity for revision surgery. In recent years researchers have undertaken studies on the possibility of enhancing the mechanical properties of PMMA by adding various admixtures in different concentrations. In this study we present the results of the mechanical properties of samples made of the commercially available and widely used in orthopaedic surgery PMMA bone cement (Palamed® Heraeus) that was admixed with glassy carbon (GC) using different concentrations. All samples were subjected to compression testing. Compression reflects the load mechanism acting on PMMA in the human body after TJR implantation. The study involved comparing selected mechanical parameters of both samples prepared according to the manufacturer’s instructions and samples prepared with the addition of GC with grain sizes of 0.4–12 μm and 20–50 μm. Although this material can potentially increase the mechanical strength of PMMA, serious contamination with GC can lead to PMMA polymerization impairment due to the thermal properties of GC and, consequently, affect the mechanical properties of PMMA. GC was added in the following w/w concentrations: 1, 2, 3, 5, 8 and 10 %. Results revealed a significant decrease in the compression strength of PMMA following the addition of 20–50 μm GC, which resulted from the disturbances in standard polymerization process conditions (time and temperature). Interestingly, the addition of 0.4–12 μm GC did not affect significantly the compressive strength of the material in the tested range of concentration.

Every year millions of people around the world suffer from joint and bone diseases and require orthopaedic surgery. Owing to its unique properties such as biocompatibility and ability to bond bones with orthopaedic implants, poly methyl-methacrylate (PMMA) is among the most widely used polymer composites for bone cements in orthopaedic and trauma surgery. On the other hand, this material is characterized by low mechanical properties, which can lead to accelerated implant loosening in aggressive environments, such as the human body. Over the years, researchers have studied PMMA, especially its failure mechanism. Various additives to PMMA have been proposed to enhance the mechanical properties of this material. This study investigated the effect of mixing PMMA with α-TCP (PMMA/α-TCP bone cement composite) and β-TCP (PMMA/β-TCP bone cement composite) on its mechanical properties. The study was conducted on commercially available PMMA (Haraeus Palamed) mixed with α-TCP and β-TCP in different concentrations. TCP has bacteriostatic properties and, as a bone compatible material, it stimulates bone regeneration and bone ingrowth, which highly increases the survival rate of PMMA bonding. However, the addition of particles to PMMA can affect mechanical properties of bone cements. In this study, the effects of 0, 1, 2, 3, 5, 8 and 10% dry mass concentration of TCP in bone cement on the mechanical properties of PMMA were investigated. Samples were subjected to compressive loading. This loading mode is typical of the human body after joint prosthesis implantation. The analysis involved comparing selected mechanical parameters of samples prepared according to manufacturer’s instructions and of samples prepared with the addition of α-TCP and β-TCP. Results demonstrated that the addition of β-TCP, whose crystals are triangular, did not affect the mechanical properties of PMMA. On the other hand, the addition of more than 3% dry mass α-TCP, the inner structure of which is hexagonal, led to a slight yet significant decrease in the compressive strength of PMMA.