A Forward−Backward Splitting Equivalent Source Method Based on S−Difference

The regularization method has a direct impact on the accuracy of the reconstructed sound field in the process of inverse calculation of near−field acoustic holography using the equivalent source method. To expand the frequency range of sound field reconstruction and improve computational accuracy, a forward-backward splitting equivalent source method based on s−difference was proposed, which uses the ratio of the output results of the broadband acoustic holography algorithm as the regularization parameter. Numerical simulations of single source and coherent source sound fields were conducted under different frequency conditions to analyze the performance of the forward-backward splitting regularization algorithm based on s−difference, and experimental verification was performed. The simulation results show that the proposed method can accurately reconstruct the sound field in a wider frequency range, and has high accuracy in reconstructing the sound field of low−frequency coherent sources. The experimental results demonstrate the accuracy and effectiveness of this method in reconstructing mid−to−low−frequency sound fields

Experimental Evaluation for the Interference-fit Electromagnetic Rveting Joint with Headless Rivet

Abstract Electromagnetic riveting (EMR) technology as a relatively new mechanical joining process has many advantages compared to traditional riveting methods. However, it needs to be investigated whether the traditional pressing riveting can be replaced by EMR process in aerospace manufacturing engineering. Therefore, in this paper, the differences of riveting quality between automatic riveting and handheld EMR were compared by riveting and mechanical experiments including the uniformity of interference fit, shear and pull-off strength and fatigue life of the joints respectively. It was observed that the interference fit of the riveting joint using EMR is more uniform along the axial direction of rivet than that of automatic riveting. In addition, the overhang of the rivet was difficult to control by handheld EMR, so the quality of rivets for EMR was poorer than that of automatic riveting. Thus, the shear and pull-off strength and fatigue life of EMR joints were affected by the quality of rivets, and a longer rivet is needed for the EMR.</jats:p

Stress analysis and damage evolution in individual plies of notched composite laminates subjected to in-plane loads

This work aims to investigate local stress distribution, damage evolution and failure of notched composite laminates under in-plane loads. An analytic method containing uniformed boundary equations using a complex variable approach is developed to present layer-by-layer stresses around the notch. The uniformed boundary equations established in series together with conformal mapping functions are capable of dealing with irregular boundary issues around the notch and at infinity. Stress results are employed to evaluate the damage initiation and propagation of notched composites by progressive damage analysis (PDA). A user-defined subroutine is developed in the finite element (FE) model based on coupling theories for mixed failure criteria and damage mechanics to efficiently investigate damage evolution as well as failure modes. Carbon/epoxy laminates with a stacking sequence of [45°/0°/−60°/90°]s are used to investigate surface strains, in-plane load capacity and microstructure of failure zones to provide analytic and FE methods with strong validation. Good agreement is observed between the analytic method, the FE model and experiments in terms of the stress (strain) distributions, damage evaluation and ultimate strength, and the layer-by-layer stress components vary according to a combination effect of fiber orientation and loading type, causing diverse failure modes in individuals

Effect of interference percentage on damage mechanism of carbon fiber reinforced plastics laminate during interference-fit bolt installation

The interference-fit joint of composite laminates is widely used in assembly of thin-walled components in aviation product, but the interference percentage has a significant effect on squeezed damage which may reduce structural reliability. An investigation is conducted into the in-plane stress distribution and initial damage mechanism of symmetrical carbon fiber reinforced plastics laminates during the interference-fit bolt installation process. Considering the elastic deformation of the bolt, a general stress distribution model around the interference-fit joint is established with complex potential method. The initial damage mechanism of carbon fiber reinforced plastics laminates is characterized and critical interference percentages without damage are obtained with the mixed damage criteria. The effects of ply orientation and interference percentage on damage mechanism of each individual layer are discussed. Then, extensive finite element models with USDFLD subroutine of interference fit process are used to analyze and simulate the stress distribution and squeezed damage which are validated by strain measurement and micrographs by experiments subsequently. It is observed that theoretical solutions fall within the finite element results. The matrix tensile damage occurs first, and the critical interference percentages decrease from 1.10% to 0.85% with bolt diameters varying from 4 to 10 mm. </jats:p

Multi-scale modeling and mechanical performance analysis of finger seals with plain woven C/C composite

Abstract The application of carbon fibers reinforced carbon matrix (C/C) composite can solve the local wear of metallic finger seals effectively. However, the performance of C/C composite finger seal is complex and variable, which further decreases the sealing performance and life. Therefore, a method of multi-scale modeling and mechanical performance analysis for plain woven C/C composite finger seals was conducted. The circumferential finger beams of C/C composite were modeled by multi-scale structural analysis and weaving simulation. The radial static and dynamic stiffness characteristics of finger beams were investigated. The results showed that the radial static stiffness of the finger beam with three layers was about 3 times that with single layer. The radial stiffness of circumferential finger beams presented a periodic distribution pattern with a period of 90°. The radial dynamic stiffness of C/C composite finger beams increased with the excitation displacement amplitude and rotor speed. But the magnitude and fluctuation degree of dynamic stiffness were greater than those of static stiffness. A large difference in radial stiffness will lead to local wear and hysteretic leakage. This study lays a foundation for the analysis and optimization of the hysteresis and wear characteristics of C/C composite finger seals