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In recent years, Ti--Ta alloy has become a hot material in orthopedic implants. At the same time, the metal lattice structure with a negative Poisson's ratio has a great prospect in the application of implants due to its unique mechanical properties. Herein, an antichiral three-dimensional polyhedron (A3P) lattice structure with negative Poisson's ratio is designed. This lattice structure is prepared by laser powder bed fusion (LPBF) technology using Ti--Ta alloy as the feedstock material. The surface morphology and relative density of the Ti--Ta samples built with different laser scanning speeds are compared for the optimization of the Ti--Ta's LPBF parameter. Then, the A3P structure of the Ti--Ta alloy is fabricated using the optimized LPBF parameters. The negative Poisson's ratio effect of the A3P structure is verified by finite element analysis (FEA) and compared with experimental results. The compression test results show that the yield strength and elastic modulus of the A3P structure are 9.2 MPa and 0.14 GPa, respectively, which is suitable for the orthopedics application. A3P structure has higher fracture energy compared with diamond structure, indicating it can absorb more energy in the fracture process. A3P shows a promising prospect in the application of orthopedics implantation. [ABSTRACT FROM AUTHOR]

Aiming at the lack of effective load analysis method, a load analysis method of cycloidal pin wheel based on minimum deformation energy was proposed. By introducing the minimum deformation energy, the actual number of simultaneous meshing teeth was determined, and the real load characteristics in line with the engineering practice were obtained. Through finite element simulation and measurement experiments, the correctness and effectiveness of the theoretical analysis method of minimum deformation energy introduced were verified. The results show that the predicted maximum possible number of teeth, the results calculated by the principle of minimum energy and the results of finite element analysis are all 16 teeth. The transmission error curves of theoretical calculation, actual measurement and simulation analysis show a relatively consistent parabolic trend, and the maximum fluctuation ranges are 3. 83', 3. 66' and 3. 70' respectively. [ABSTRACT FROM AUTHOR]

Due to the large wall thickness difference and serious instability in the large-scale ring rolling process, most studies on the feed curve are not suitable for a large-scale ring. The production cost of the large-scale ring is high, and if plastic instability occurs, it will cause a great waste of resources. Therefore, in this study, a staged feed strategy based on the evolution of ring instability is proposed with the objective of controlling the rolling stability of a large-scale ring. Firstly, based on the law of rolling instability evolution, the rolling stage during the rolling process is divided. Secondly, the coordination of all rolling stages is proposed as a factor to design the feed curve. The feed scheme is determined using the central composite design (CCD) method, and then the established mathematical model is applied to obtain the radial feed curves of a large-scale flat ring with a 5 m diameter for different schemes. Next, the designed feed curve was submitted to finite element method (FEM) simulation. According to the FE simulation results, a rolling map for controlling roundness error, eccentricity and vibration is established. Finally, the feed curve in the stable region is input to the FE simulation and the production trial to obtain the results of roundness error, eccentricity and vibration. A comparison of the simulation and production trial results shows that they are in good agreement, which proves the reliability of the feed curve designed based on the stable rolling region in the roll map. Moreover, the machining amount for both the simulation and production trial is below the maximum machined value. [ABSTRACT FROM AUTHOR]

Composites are widely used in aircraft structures that have free edges and are vulnerable to impact events during manufacturing and maintenance. On-edge impact may have a great contribution in terms of the compression strength loss of composites, but the influence remains unclear. This paper presents experiments and simulations of carbon-fiber-reinforced plastic (CFRP) materials with on-edge impact and compression after edge impact (CAEI). On-edge impact damage was introduced to the composite laminates through the drop weight method with 4, 6, 8 and 10 J impact energies, respectively. A special guide-rail-type fixture was used in the compression tests in which strain–force and load–displacement relationships were obtained. A continuous-step finite element model was proposed to simulate impact and compression. Continuum shell elements and Hashin failure criteria were used to simulate in-ply damage, and interlaminar damage was modelled by cohesive elements. The model was validated by correlating the experimental and numerical results. The investigation results revealed the relationships of the damage size and residual strength with the different impact energies. The crack length and delaminated area grow with the increase in impact energy. The residual compressive strength follows a downward trend with increasing impact energy. [ABSTRACT FROM AUTHOR]

The Wu‐Carlsson displacement‐based weight function method is extended to obtain the mode I and mode II weight functions for the edge‐ and centre‐cracked discs. Compared with Fett's direct adjustment weight functions for the edge‐cracked discs, the present weight functions are more accurate and are applicable for a wider range of crack lengths. Using the present weight functions, extensive and highly accurate mixed‐mode stress intensity factors are obtained for the cracked discs subjected to diametrically compressive forces. Assuming perfect contact and using Coulomb friction law and the present weight functions, the mode II stress intensity factors for the cracked discs with consideration of friction are obtained and widely compared with the corresponding results from finite element analyses. [ABSTRACT FROM AUTHOR]

Single edge notched tensile specimens (SENT) are used to measure the fracture toughness of a woven textile composite. Both, the finite element method and available stress intensity factor (SIF) solutions to the SENT are used to calculate the SIF. Linear elastic fracture mechanics, the size effect law and cohesive zone model are used to determine the critical energy release rate. In this note, the importance of using an accurate SIF solution and a proper method to determine the fracture toughness are demonstrated. [ABSTRACT FROM AUTHOR]

• Accurate and wide-range weight functions of an eccentric crack in a finite sheet with constrained lateral edges are derived. • 3D weight function methods for two eccentric and asymmetric hole-edge surface and corner cracks are established. • The presented approach is accurate and much faster than FEM for SIF calculation. • The present SSWFM can be used to obtain 3D SIFs of most of the surface and surface-corner crack originating from a hole. Stress intensity factors (SIFs) of two eccentric and asymmetric surface cracks and surface-corner cracks at a hole are rare in the literature, since the problem is too complicated to be tackled by analytical methods and too costly by numerical approaches. A 3D slice synthesis weight function method (SSWFM) is developed to compute their 3D SIFs. The results agree well with those from finite element method (FEM). The SSWFM is about 450 times faster in calculation of the SIFs than FEM/Franc3D, and is very useful for 3D fatigue crack growth analyses of complicated surface and corner cracks at a hole. [ABSTRACT FROM AUTHOR]

• SSWFM for unsymmetric surface cracks and surface-corner cracks at a hole is established. • The 3D SIFs obtained by SSWFM is accurate. • SSWFM is 500 times faster than FEM for SIF calculation. Two unsymmetric surface cracks and a combination of surface and corner cracks emanating from a circular hole are frequently encountered in many engineering structures, especially in airframes. Their stress intensity factors are critical for damage tolerance analyses. However, compared to cases of a single crack and symmetric double cracks that have been extensively analyzed in the literature, the present unsymmetric surface cracks and surface/corner cracks emanating from a circular hole are much more complicated because more geometric variables are involved. In this paper, the slice synthesis weight function method for two unsymmetric hole-edge corner cracks developed recently by the present authors is further extended to calculate the stress intensity factors (SIFs) of two unsymmetric surface cracks and a combination of surface and corner cracks at a hole. The obtained SIFs are verified by comparing to limited solutions in the existing literature and also extensive finite element analysis. Very good agreements are achieved. Compared to 3D finite element analysis, the present slice synthesis weight function analysis is remarkably more efficient, and therefore can enhance the current capability of fatigue and fracture analyses for structures with unsymmetric surface and corner cracks at a circular hole. [ABSTRACT FROM AUTHOR]

Circular concrete-encased concrete-filled steel tube (CFST) consists of the circular inner CFST and circular outer reinforced concrete. In this paper, the axial compressive behaviour of the composite column is experimentally and analytically investigated. Ten concrete-encased CFST specimens, four reference CFST specimens and two reference reinforced concrete specimens were tested; the parameters include the ratio of the steel tube diameter to the column diameter and the concrete strength. The influence of these parameters on the axial load in relation to axial strain, ultimate compressive strength and ductility is discussed. A finite-element model is established, where a stress against strain model is suggested for the concrete confined by circular stirrups located outside the steel tube. The predictions are verified against the test results of the stub columns. Analysis is then performed to investigate the internal force distribution and stress development during the loading process. Parametric analysis is conducted to discover the influence of critical parameters. Finally, simplified superposition methods are suggested to predict the ultimate compressive strength. [ABSTRACT FROM AUTHOR]

The crack band model of Bazant and Oh (1983), referred to as the CBBO, is frequently used in material damage and softening analysis. Care should be taken in the implementation of the CBBO using the finite element (FE) method through commercial codes, since different strain measures are used which can lead to mesh dependency. A method is proposed to enforce mesh objectivity for engineering strain, Green–Lagrange strain and logarithmic strain when the CBBO is used in solving problems using commercial FE codes. The proposed method is shown to produce mesh objective solutions for strain softening situations. [ABSTRACT FROM AUTHOR]

Abstract: A series of tests were conducted on curved concrete filled steel tubular (CCFST) trusses with curved CFST chords and hollow braces subjected to bending. A total of 8 specimens, including 4 CCFST trusses, 2 straight CFST trusses (referred to as CFST trusses) and 2 curved hollow tubular trusses were tested to study the effect of the rise-to-span ratio and infill concrete on the flexural performance of CCFST trusses. Different failure modes were observed: bending failure for CFST trusses, bending-shear failure for CCFST trusses and local buckling failure for hollow tubular trusses. The experimental result showed that the stiffness and load-carrying capacity of CCFST trusses were larger than those of CFST trusses, but the CCFST trusses experienced a joint failure with relatively low ductility. Meanwhile, the infill concrete provided support to the steel tubular chords and increased the stiffness, load-carrying capacity and ductility. A finite element analysis (FEA) model of the CCFST trusses was developed and verified by the test results. The model was then used to investigate the mechanical behaviour of the truss by full range analysis. A simplified model was proposed to predict the elastic stiffness considering both the flexural and the shear deformation. The load-carrying capacity of the CCFST structure was also discussed. [Copyright &y& Elsevier]

• Accurate and wide-range weight functions of two hole-edge cracks are derived. • A 3D weight function method for two unsymmetrical corner cracks is established. • It is accurate and much faster than FEM for SIF calculation. Two unsymmetric through and quarter-elliptical corner cracks at a circular hole are frequently encountered in aircraft structures. Stress intensity factors for these crack geometries are the prerequisite for aircraft damage tolerance analysis. However, compared to single and symmetric double crack(s) case, the present two unsymmetric through and corner cracks at a hole is much more complicated because more geometric variables are involved. In the present article, the two-dimensional displacement-based weight function method is extended to derive the weight functions of two unsymmetric hole-edge cracks. Accurate and wide-range weight functions and stress intensity factors are obtained. The two-dimensional weight function for the hole-edge cracks is further used in the slice synthesis weight function method to compute stress intensity factors for two unsymmetric quarter-elliptical corner cracks at a circular hole. The solution accuracy is extensively verified through comparisons to stress intensity factors obtained using finite element analysis. Compared to 3D finite element method, the present slice synthesis weight function method is 500 times faster, and therefore can provide accurate and very efficient tool for fatigue and fracture analysis of structures containing through and quarter-elliptical corner hole-edge cracks. [ABSTRACT FROM AUTHOR]

This paper focuses on improving the quality of aluminum rectangular tube in the cold drawing process. The newly developed drawing tools (i.e., the drawing die and the plug) which are considered as one of the most significant factors influencing the final forming quality are proposed. The new-type drawing die is designed with the 'convex hull' shape in sizing zone corner and the plug is featured with a 'boss club' structure in sizing zone. The equivalent plastic strain, drawn tube's dimensional accuracy, contact stress distribution, and drawing load have been analyzed for the conditions under which the original tools and the new-type ones have been used, respectively, based on finite element simulations. The simulation results show clearly that the discrepancy of plastic strain in the axial cross section and the tube axial elongation are smaller when the new-type die is employed, which indicates the more uniform metal deformation and steady material flow. Besides that, the fluctuation of wall thickness is also unobvious showing the new-type die is very helpful to improve the tube dimensional accuracy. The newly developed plug can cause higher compressive plastic strain and contact stress, which are crucial to guaranteeing the high surface quality. An experiment on the cold drawing process of the aluminum rectangular tube has been performed. The comparisons of the drawn tube dimensions, e.g., height/width and wall thickness, have been made between simulation results and practical production. Meanwhile, the surface finish has also been measured. The experimental result exhibits that the drawn tube can better fulfill the requirements of the design and usage when the new-type tool is adopted. [ABSTRACT FROM AUTHOR]

ording to the distribution characteristics of equivalent plastic strain (PEEQ) in radial-axial ring rolling, the plastic deformation zones in cross section were established. A 3D rigid-viscoplastic finite element model (FEM) which was controlled adaptively was applied to investigate defects that occurred during ring rolling under ABAQUS software. PEEQ, stress, and temperature distributions in different deformation zones have been analyzed in this study. Strain peaks were found in the cross-section corners. Moreover, it was investigated that non-uniform strain, stress, and temperature distributions in the ring tend to cause non-uniform microstructure and properties. Therefore, forming defects and microstructure damage would appear in cross-section corners due to the high-strain deformation. Based on the new developed FEM of the radial-axial ring-rolling process and comprehensive numerical simulations, the size effects of feed rate and lubrication conditions on strain and temperature distributions and their uniformity were investigated by 3D coupled thermomechanical FE simulation. The results have good agreement with experiment. The achievements of this study can provide basis for quality control and technical guidance. [ABSTRACT FROM AUTHOR]

• An analytical method is developed to analyze the stiffened panel with multiple collinear cracks. • The present stress intensity factor and plastic zone size are verified by the existing results from literature and FEM. • Compared to FEM, the present method is efficient. • The present method is efficient for predicting the behavior of stiffened panel with multiple site damage. Stiffened panel with multiple site cracks has been a great concern in the aviation industry and academia. In this paper, an analytical method for solving the stress intensity factor and strip yield model with coalesced plastic zone is developed based on the superposition principle, displacement compatibility and weight function method. It is then applied to obtain the stress intensity factors and plastic zone sizes for stiffened panels with two and three collinear cracks. The determined stress intensity factors and plastic zone sizes are compared with those from finite element analysis and existing literature. The present method is demonstrated to be accurate and efficient in calculating the stress intensity factor and plastic zone size for residual strength and fatigue crack growth prediction of stiffened panel with multiple site cracks. [ABSTRACT FROM AUTHOR]