Strain Localization in Combined Axial-Torsional Testing on Kaolin Clay

A series of combined axial-torsional tests were performed to study the 3D mechanical behavior of kaolin clay in an undrained condition. Using the digital image analysis technique, discrete local deformation of the surface of a hollow cylindrical specimen under loading was recorded. A linear interpolation method was used to generate a continuous deformation and strain field of the specimen based on the recorded discrete local deformations. Evolution of shear band was vividly visualized and recorded during the loading process for various inclinations of major principal stress. The theory of strain localization on continuous bifurcation was briefly reviewed and applied to the Mohr-Coulomb model, and a single hardening model incorporating the concept of loading-history-dependent plastic potential was developed by the writers. The largest critical plastic modulus and orientation of the shear bands were predicted by using the theoretical solution. Significant disagreement was observed between the experimental results and theoretical predictions related to the initial occurrence of strain localization and the inclination of fully developed shear bands.     

Coupled model for the non-linear analysis of anisotropic sections subjected to general 3D loading. Part 1: Theoretical formulation

A numerical model for the coupled analysis of arbitrary shaped cross sections made of heterogeneous-anisotropic materials under 3D combined loading is formulated. The theory is derived entirely from equilibrium considerations and based on the superposition of the 3D section’s distortion and the traditional plane section hypothesis. 3D stresses and strains fields are obtained as well as a section stiffness matrix reflecting coupling effects between normal and tangential forces due to material anisotropy. Traditional generalized strains and stresses are maintained as input and output variables. The proposed model is suitable as a constitutive law for frame elements in the analysis of complete structures.     

Damping Factors and Fatigue Notch Factors of Pseudoelastic NiTi‐Shape Memory Alloys

Pseudoelastic NiTi‐ shape memory alloys (SMAs) provide a high damping capacity and can be used in order to achieve a reduction of peak loads being caused by unexpected shock loading. These “pseudoelastic” properties are related to the formation of martensite M from austenite A, which has been induced by stress; they allow to refer to SMAs as functional materials. Furthermore, these functional materials can operate at high stresses and thus, have to withstand severe mechanical loadings like classical structural materials. In combination, these characteristics provide opportunities for technical applications, e.g., to reduce vibrations or to reduce peak loads caused by shock loading. An extensive knowledge of the functional and structural fatigue behaviour of the material is required to design SMA components. NiTi hollow shaft samples and solid shaft samples have been tested under cyclic torsional loading conditions in a load‐controlled mode. By using these two geometries the influence of the sample geometry on the fatigue behaviour can be investigated. In addition, a test programme has been elaborated in order to investigate the behaviour of the material when subjected to bending. The experimental data have been evaluated describing the transformation behaviour induced by stress concerning transformation stress, apparent shear modulus of the austenite G_A and apparent stiffness τ_Ms (describing the slope of the shear stress‐strain‐curve in the transformation range G_A‐M). These parameters naturally depend on the cycle number, the load amplitude as well as the temperature. Engineering failures are often associated with the presence of notches. In this context, torsion tests on notched samples are planned to be carried out in order to assess the resulting data based on the results obtained from the notch free samples. This will allow to derive simple design rules based on fatigue notch factors, which are needed for engineering design.     

非标准试样高温拉-扭引伸仪的剪切应变信号换算

分析了MTS632．68c-01高温拉-扭引伸仪测量扭转应变信号的基本工作原理，据此推导出在非标定情况下使用该引伸仪时，其输出扭转应变信号的公式和简化计算式。实验验证表明，简化计算式的精度较高，最大相对误差为0．77％，可以满足测试精度的要求，从而大大扩充了该引伸仪的使用范围。     

Composition and size dependent torsion fracture of metallic glasses

The fracture of metallic glasses(MGs)of different compositions and sizes down to micrometers under torsion loading were systematically investigated.Contrary to the flat shear fracture along the circumfer-ential plane as commonly supposed under torsion,we find that the torsion fracture of metallic glasses can deviate from flat shear plane,and the fracture angle is closely dependent on the composition and the size of MG samples.With a conversion method,we show that the torsion fracture of both millimeter-and micrometer-sized MGs can be described by the ellipse fracture criterion as originally proposed for the tension fracture.The deviation from the circumferential shear plane under torsion is further shown to intrinsically relate to the fracture toughness of MGs.The tougher MG tends to have a smaller fracture angle with respect to the maximum shear plane,and vice versa,indicating a correlation between the fracture toughness and pressure/normal stress sensitivity in MGs.Our results provide new insights on the fracture mechanism and are helpful to design and control the deformation and fracture behavior of MGs under torsion loading.     

Multi-cell carbon fibre composite box beams subjected to torsion with variable twist

The structural performance of multi-cell carbon fibre composite box beams when subjected to constrained torsional loading is examined in this paper. A simplified analytical procedure for determining the constrained torsional response of a specific class of multi-cell carbon fibre composite box beams is outlined in some detail. The constrained condition analysed is that of the cantilevered multi-cell beam with torque applied at the free end of the beam. Overall elastic couplings in the beams between bending, torsion and axial effects are eliminated from the analysis process through the use of constituent laminates for the thin walls of the cross-sections which are symmetrically layed-up about their own mid-planes and in such a manner that they possess in-plane orthotropy. The analysis procedure employed makes use, essentially, of the existing theories of torsion developed for isotropic construction and these are then suitably modified to account for the non-isotropic nature of the typical carbon fibre composite material. The resulting approach is shown to be able to predict the structural response of the multi-cell composite beams with a considerable degree of accuracy and comparisons between the theory and the results from finite element numerical modelling are shown to give close agreement. The torsional and warping rigidities of the composite multi-cell beams are calculated in a procedure which makes use of the appropriate membrane engineering elastic constants of the individual thin composite walls and the constituent thin walls can have different lay-up configurations provided the stiffness distribution around the sections is of a symmetrically disposed nature in order to preclude the influence of overall elastic couplings.     

Comparison between solid and hollow reinforced concrete beams

Comparison between test results of seven hollow and seven solid reinforced concrete beams is presented. All of the fourteen beams were designed as hollow sections to resist combined load of bending, torsion and shear. Every pair (one hollow and one solid) was designed for the same load combinations and received similar reinforcement. The beams were 300 × 300 mm cross-section and 3,800 mm length. The internal hollow core for the hollow beams was 200 × 200 mm creating a peripheral wall thickness of 50 mm. The main variables studied were the ratio of bending to torsion which was varied between 0.19 and 2.62 and the ratio in the web of shear stress due to torsion to shear stress due to shear force which was varied between 0.59 and 6.84. It was found that the concrete core participates in the beams’ behaviour and strength and cannot be ignored when combined load of bending, shear and torsion are present. Its participation depends partly on the ratio of the torsion to bending moment and the ratio of shear stress due to torsion to the shear stress due to shear force. All solid beams cracked and failed at higher loads than their counterpart hollow beams. The smaller the ratio of torsion to bending the larger the differences in failure loads between the hollow and solid beams. The longitudinal steel yielded while the transverse steel experienced lower strain values.     

晶尚名苑短肢剪力墙结构设计

通过工程实践简述短肢剪力墙结构体系的构成、特点,以及利用该结构进行实际设计工作应注意的一些问题,比如计算方法、剪力墙布置方式、配筋方式以及连梁、转角窗的设计等。可供工程设计应用时参考。     

Torsion analysis of thin-walled beams including shear deformation effects

The first part of the paper develops a theory for the torsional analysis for open thin-walled beams of general cross-sections which accounts for shear deformation effects. Statically admissible stress fields are postulated in agreement with those resulting from the Vlasov thin-walled beam theory. The principle of stationary complementary energy is then adopted to formulate the governing field compatibility condition under the stress fields postulated. The naturally arising boundary terms are found to relate the warping deformations to the internal force fields. A torsion beam example is solved using the new theory in order to illustrate its applicability to practical problems. The second part of the paper implements the solution numerically in a force-based finite element context. Two finite elements are developed by assuming linear and hyperbolic bimoment fields. The FEA solutions are shown to provide lower bound representations of the stiffness when compared to those based on conventional beam theories founded on postulated kinematic assumptions.     

Stability of circular cylindrical steel shells under combined loading

Circular cylindrical shells made of steel are used in a large variety of civil engineering structures, e.g. in off-shore platforms, chimneys, silos, tanks, pipelines, bridge arches or wind turbine towers. They are often subjected to combined loading inducing membrane compressive and/or shear stress states which endanger the local structural stability (shell buckling). A comprehensive experimental and numerical investigation of cylindrical shells under combined loading has been performed which yielded a deeper insight into the real buckling behaviour under combined loading . Beyond that, it provided rules how to simulate numerically the realistic buckling behaviour by means of substitute geometric imperfections. A comparison with existing design codes for interactive shell buckling reveals significant shortcomings. A proposal for improved design rules is put forward.