Search

The compression behavior of a damaged I-section stiffened panel repaired by the bolted metal patch method is studied experimentally and numerically by the finite element method in this paper. In the finite element model, the bolt was simulated by a combination of beam elements coupled to rigid contact surfaces, the coupling failure criterion and a new delamination criterion were used to analyze the failure of composite laminates and bonding interfaces, respectively. The repairing effects of the mechanical fastening method are compared with the panels with damage. The results show that the load-carrying capacity of the repaired panel increases significantly compared with the panel with damage. The experimental results validate the proposed finite element model. Finally, an improved repair configuration is proposed based on the finite element simulation. This shows that the presented repair is useful and effective to repair the damaged composite structures. [ABSTRACT FROM AUTHOR]

The patch debonding is one of the most serious failure modes of reducing the efficiency of composite repair. In this study, a three-dimensional finite element method is used to analyze the initiation and progression of cohesive failure of the semicircular patch repairing crack emanating from a semicircular notch root. The stress intensity factor and the debonding initiation stress are calculated. The obtained results show that the debonding propagation can be decreased by optimizing the geometrical properties of the composite patch and the adhesive. [ABSTRACT FROM AUTHOR]

Cellular structures have been widely studied and employed in engineering because of their excellent mechanical properties. To enrich the geometric diversity of cellular structures, we proposed two novel chiral cellular structures composed of half-periodic and full-periodic cosinoidal beams respectively in this paper. The in-plane elastic properties were studied by a combination of the energy method and the finite element analysis, and verified by the experimental test. The influences of geometric parameters on the elastic constants were analyzed. Then, the elastic properties of the two structures as well as the V-shaped chiral structure were compared. Finally, error analysis was carried out on the theoretical models. Results show that: (1) the two structures own considerably low equivalent elastic moduli and extremely high strain capabilities, and possess certain in-plane elastic coupling effects; (2) the elastic properties of the two structures are highly tunable with the variations of geometric parameters; (3) the elastic moduli of the two structures are lower than that of the V-shaped structure, and the structure with half-periodic beams exhibits the lowest in-plane stiffness and the highest strain capabilities; (4) the theoretical models without considering the internal axial force are convincible in predicting the elastic properties when the corresponding chord ratio is larger than 0.2. Generally, the proposed structures have great potential as flexible structures for morphing application. [ABSTRACT FROM AUTHOR]

• The interaction between multiple inclusions and cracks in a finite plane due to a uniform temperature change is investigated. • The represented method combines the Eshelby's equivalent inclusion method and distributed dislocation method. • Both interior Eshelby's tensor and exterior Eshelby's tensor are used in the presented method. The purpose of this paper is to study the interaction between multiple elliptical inclusions and straight cracks in a finite plate due to a uniform temperature change. In this solution, Eshelby's equivalent inclusion method involving both interior Eshelby's tensor and exterior Eshelby's tensor is applied to calculate the thermal stress fields of an infinite plate containing multiple elliptical inclusions under a uniform temperature change first. Then the multiple cracks and the boundary are modeled by continuous distributions of dislocation densities in an infinite plate. Based on the stress boundary conditions of the cracks and boundary, a system of singular integral equations with Cauchy kernels are obtained. After solving the singular integral equations with Gauss–Chebyshev numerical quadrature, the stress intensity factor of each crack can be calculated. Besides, the finite element method is employed to examine the accuracy and efficiency of the presented method. Finally, the effects of the material and geometric parameters on the normalized stress intensity factors of the cracks are studied. [ABSTRACT FROM AUTHOR]

A novel star-shaped cellular structure with great elastic properties is proposed as candidate for multiple morphing applications. Theoretical derivations and finite element analysis are conducted to study the mechanics of the structure. Results show that the in-plane moduli of the structure can be extremely lower than those of the base material, while the maximum global strains reach, dozens of times, the limit elastic strain of the base material. The proposed structure also exhibits lighter weight, lower in-plane moduli and larger strain ratios than the existing semi-sinusoidal structure, which indicates lower actuation requirements and greater strain capabilities for morphing applications. [ABSTRACT FROM AUTHOR]

Cellular structures are potential candidates for cores of flexible sandwich skins that are required of low in-plane stiffness for morphing and high out-of-plane stiffness for load-bearing, as well as zero Poisson's ratio for one-dimensional morphing. In this paper a novel cellular structure of close-to-zero Poisson's ratio with trapezoidal beams is proposed to meet these requirements. The elastic properties of the structure were investigated through a combination of theoretical analysis and finite element validations. Then the effects of geometric parameters on the properties of the structure were studied and analyzed. Finally comparisons on the properties with a classical accordion cellular honeycomb were carried out. Results show that the analytical results are well matched with results of the finite element validations and the proposed structure is of a better in-plane morphing property than the conventional cellular structure. Small value of thickness-to-length ratio, large values of horizontal sub-beam proportion ratio along x -direction and vertical to trapezoidal beam thickness ratio are recommended for balancing the in-plane and out-of-plane properties. [ABSTRACT FROM AUTHOR]

Cellular structure cores are potential candidates for support structures of flexible skin. The skin requires low in-plane and high out-of-plane stiffness of the support structure. To overcome these problems, a cellular structure with in-plane corrugated cosine beams having close-to-zero Poisson’s ratio to significantly reduce unnecessary stress and strain for one-dimensional morphing application was developed. The elastic properties were theoretically analyzed by energy methods, and verified by finite element analysis. Results show that better in-plane morphing and out-of-plane load-bearing capabilities can be obtained with larger height-to-length ratio, spacing-to-length ratio and vertical beam to cosine beam thickness ratio as well as smaller thickness-to-length ratio. Comparisons on properties with conventional accordion honeycomb were carried out. The results reveal that the cellular structure is of lower in-plane elastic modulus, which shows better in-plane property but weaker out-of-plane load-bearing capability. However, the out-of-plane load-bearing capability can be reinforced by increasing the height-to-length ratio and vertical beam to cosine beam thickness ratio. [ABSTRACT FROM AUTHOR]

Support structures are needed due to the complexities of induced structural, thermal and process factors in Selective Laser Melting (SLM). To date, little systematic study is found to unveil the support removability by a post-machining process. This paper presents an experimental study of removing 316L stainless steel cone and block supports by milling. The effect of different supports is identified by the variation in the microhardness distribution and microstructure of the workpieces. The milling performance of cone and block supports at different cutting depths is studied on the surface finish, surface roughness, milling force, and tool wear and chip formation. The cone supports are subjected to severe collapse, whilst the block supports are mainly removed by localized shearing. The milling force and specific cutting energy of cutting block supports are lower than that of cone supports, and so is the tool wear. A finite element method (FEM) model is developed to explain the removal mechanisms. The results of this study provide an essential reference and unique insight into removal of metal support structures. Moreover, the removability of supports, which is derived from the post-processing stage, should be considered as a new factor in the support design for additive manufacturing. Unlabelled Image • The effect of different support structures is identified by the variation in the microhardness distribution and microstructure. • A systematic study unveils the metal support removability in selective laser melting (SLM) by milling. • Milling performance between cone and block support structures is compared at different cutting depths. • A finite element method (FEM) model is developed to explain the support removal mechanisms. [ABSTRACT FROM AUTHOR]

• An anti-tetrachiral cellular structure composed of flexible beams is proposed. • Closed-form solutions of elastic constants of the structure are obtained. • The light-weight structure shows highly tunable elastic moduli and Poisson's ratio. To provide better solutions for compliant structures, in this paper, an anti-tetrachiral cellular structure with low in-plane stiffness and high auxeticity is proposed. Closed-form solutions of the structure's elastic indicators are theoretically obtained via the energy method, and then numerically verified by using finite element method. The in-plane elastic performance is also discussed through parameter analysis. Results show that the structure has very much low effective moduli and negative Poisson's ratio, exhibiting significantly enhanced deformability and auxeticity. Compared with the conventional anti-tetrachiral structure with rigid central rings, the proposed structure with fully flexible beams shows superior in-plane compliance. As a kind of auxetic structure with highly tunable effective moduli and Poisson's ratio, the proposed structure has great engineering potential in developing new types of morphing, protecting or buffering structures in aerospace, marine, medical and other fields. [ABSTRACT FROM AUTHOR]

• A distinctive 2D chiral cellular structure is studied through energy-based method. • The in-plane elastic constants and coupling effects are comprehensively investigated. • The effects of the parameters on the in-plane elasticity are concretely discussed. • The structure shows great potential for a wide range of engineering applications. A 2D chiral cellular structure, the unit cell of which is composed of four V-shaped wings, is studied through the energy-based method. The closed-form solutions of the in-plane elastic constants are obtained as functions of geometric parameters and verified through finite element analysis. Furthermore, the influences of geometric parameters on the elastic constants are discussed. Results show that the equivalent moduli of the structure can be several orders of magnitude lower than those of the base material, and the maximum global strains can be dozens of times those of the base material. Besides, the structure shows significant in-plane elastic coupling effects: (1) the maximum ratio of the shear to elastic strain beyond 17.2°/% and (2) the maximum ratio of the elastic to shear strain exceeding 1.52%/° (x -direction) and 1.64%/° (y -direction). As a distinctive 2D chiral cellular structure, the structure shows great potential as a candidate selection for flexible structures in engineering applications. [ABSTRACT FROM AUTHOR]

Cellular structures could obtain mechanical properties that are inaccessible with ordinary materials. A novel zero Poisson's ratio cellular structure with low in-plane moduli and great morphing capabilities for multiple in-plane morphing is proposed in this paper. Theoretical models of the elastic constants of the structure are established and verified by the finite element method. Results show that the equivalent moduli of the structure are several orders of magnitude lower and the maximum global strains are considerably larger than those of the raw material. Meanwhile, the mechanical properties possess large changing ranges under the variations of parameters. Comparisons between the proposed structure and two existing ones indicated that the proposed structure possesses better performance and larger range of material selection for in-plane tensile morphing, while with some drawbacks for the in-plane shear morphing. The proposed structure shows great potential as core for flexible skin or flexible structure for multiple in-plane morphing applications. [ABSTRACT FROM AUTHOR]