Transverse Shear Conditions Research Articles

Refined Nonlinear Deformation Model of Sandwich Plates with Composite Facings and Transversal-Soft Core

Following up on the results obtained earlier, a refined nonlinear model of static deformation of sandwich plates with transversal-soft core and facings with low stiffness of transverse shear and transverse compression is constructed for the case of cylindrical bending. It is based on the use of linear approximations in thickness for deflections of the external layers, cubic approximation in thickness for tangential displacements, and simplified three-dimensional equations of elasticity theory that can be integrated along the transverse coordinate with introduction of two unknown functions representing constant transverse tangential stresses in thickness for transversal-soft core. The kinematic relations for the facings are constructed in a geometrically nonlinear quadratic approximation. They allow, taking into account physical nonlinear behavior of the material under transverse shear conditions, the description of non-classical transverse-shear forms of stability loss (FSL) in both compression and bending conditions. Based on the generalized Lagrange variational principle, one-dimensional nonlinear equations of equilibrium and conjugation of the facings with the core by tangential displacements are constructed to describe the static deformation process with high rates of variability of the parameters of the stress-strain state (SSS).

MODELLING OF CRACK DEVELOPMENT PROCESSES IN COMPOSITE ELEMENTS BASED ON VIRTUAL CRACK CLOSURE TECHNIQUE AND COHESIVE ZONE MODEL

Fiber composites based on polymer matrices are promising structural materials that meet high requirements for strength, reliability, durability, and hardness. Therefore, composite materials are widely used as structural materials for aerospace products. The problems associated with the destruction of fiber composites were relevant at all stages of technology development. A variety of reinforcing fibers and polymer binders, as well as reinforcement schemes, allow directional control of strength, stiffness, level of working temperatures and other properties of polymer composite materials. This article discusses a methodology for experimental determination of the mechanical properties of carbon-based fiber-reinforced polymer composite materials, including the determination of the interlayer fracture toughness under loading under separation conditions using the doublecantilever beam method (DCB) and the fracture toughness under transverse shear conditions using the ENF (End-Notched Flexure) method and interlayer strength. The test results of samples of polymer composite materials with a carbon reinforcing filler with different surface densities are presented. The experimental data were used to identify the parameters of the VCCT (Virtual Crack Closure Technique) and CZM (Cohesive Zone Model) closure models used to describe the development of cracks in the composites under consideration. It was found that the parameters determining the strength of layered composites are such characteristics as interlayer strength and crack resistance. It was found that the decrease in the strength of individual layers of the composite does not always affect the current stress state of the entire structure, which is often difficult to detect experimentally, but can significantly affect the further behavior of the object under study provided that the crack develops further.

Specimen for the Determination of Fatigue Thresholds Under Cyclic Transverse Shear

We develop a basic element of the procedure of construction of the near-threshold part of the diagram of fatigue fracture for metallic materials under the conditions of transverse shear. It is proposed to use a square sample with edge cut and a force scheme of its cyclic loading. We determine the strain-stress state of a square plate with edge crack (regarded as a prototype of the proposed specimen) under the conditions of transverse shear by two independent methods (finite-element method and the method of singular integral equations). The stress intensity factor KII is determined for a broad interval of relative crack lengths with regard for the smooth contact of the crack faces and the presence of friction between the faces.

Conditions of Self-Similarity of Edge Transverse Shear Cracks in a Square Plate

We determine the stress-strain state of a rectangular plate with edge crack under the conditions of transverse shear. The conditions of self-similar crack propagation are established. We deduce a formula for the evaluation of the stress intensity factors KII via the shear stresses.

Fatigue Crack-Growth Resistance of Thermally Hardened 65G Steel Under Transverse Shear

We plot the kinetic diagrams of fatigue fracture of 65G steel under the conditions of transverse shear after different modes of heat treatment within the range of fatigue crack-growth rates covering six orders of magnitude with the use of the stress intensity factor for the evaluation of the stress-strain state in the vicinity of the crack tip. The main and auxiliary characteristics of cyclic crack-growth resistance are determined with regard for the friction of the lips of a fatigue crack. We construct the diagrams of structural strength and confirm the hypothesis that the fatigue thresholds increase with the yield strength of 65G steel under the conditions of shear.

Strength analysis of fillet welds under longitudinal and transverse shear conditions

In support of the development of improved fillet weld sizing criteria for lightweight shipboard structures, a comprehensive static strength test program using longitudinal and transverse shear specimens according to AWS B4.0 Standards has been conducted. This test program covers base material with strength ranging from 71 ksi (490 MPa) to 96 ksi (660 MPa) and weld size ranging from 1/8″ (3 mm) to 3/8″ (10 mm). This paper focuses on a traction stress based analysis of the test data as an effort to establish a unified shear strength definition for load-carrying fillet weld specimens regardless of shear loading conditions. The proposed shear strength definition proves to be effective in correlating the fillet weld strength test data of the longitudinal and transverse shear specimens. The results of this investigation demonstrate that existing shear strength definitions used by various weld sizing criteria such as those given by Class Societies have two major limitations: (1) it cannot be related to a critical stress state on experimentally observed failure plane in transverse shear specimens; (2) it underestimates shear stress at failure due to severe stress concentration at weld end in typical longitudinal shear specimens. These two limitations have been shown to be the major cause for having two significantly different shear strength values: one is transverse shear strength obtained from transverse shear specimens and the other is longitudinal shear strength obtained from longitudinal shear specimens.

Flexural behavior of general laminated composite and sandwich plates using a secant function based shear deformation theory

A secant function based shear deformable finite element model is developed for the flexural behavior of laminated composite and sandwich plates with various conditions. The structural kinematics of the plate is expressed by means of secant function based shear deformation theory newly developed by the authors. The theory possesses non-linear shear deformation and also satisfies the zero transverse shear conditions on top and bottom surfaces of the plate. The field variables are elegantly utilized in order to ensure C0 continuity requirement. Penalty parameter is implemented to secure the constraints arising due to independent field variables. A biquadratic quadrilateral element with eight nodes and 56 degrees of freedom is employed to discretize the domain. Extensive numerical tests for the flexural behavior of laminated composite and sandwich plates are conducted to affirm the validity of the present finite element model in conjunction with the improved structural kinematics. Influences of boundary conditions, loading conditions, lamination sequences, aspect ratio, span-thickness ratio, etc on the flexural behavior are investigated specifically and compared with the existing results in order to indicate the performance of the present mathematical treatment.

Determination of the Characteristics of Cyclic Crack Resistance of Steels Under Transverse Shear (A Survey)

We present a survey of works devoted to the investigation of the fatigue fracture of steels under the conditions of transverse shear. Numerous methods aimed at the determination of the characteristics of cyclic crack resistance of structural steels of different strength classes are analyzed. The analysis of the results of investigations enables us to make a conclusion about the necessity of improvement of the available methods and development of new methods for the construction of the kinetic diagrams of fatigue fracture with regard for the influence of friction of the lips of fatigue cracks on the stress intensity factor K II and the elimination of stresses in the vicinity of the crack tip.

Determination of the Stress Intensity Factor for a Transverse Shear Crack in a Beam Specimen

By the method of superposition of stressed states, we deduce a formula for the stress intensity factor KІІ under the conditions of transverse shear of an I-beam specimen. The comparison of the results of calculations with the theoretical data obtained earlier by the finite-element method reveals their satisfactory convergence within a broad range of relative crack lengths.

Free vibration and buckling characteristics of laminated composite and sandwich plates implementing a secant function based shear deformation theory

A generalized finite element modeling of recently developed secant function based shear deformation theory is formulated and implemented for free vibration and buckling characteristics of laminated-composite and sandwich plates. The shear deformation is expressed in terms of a secant function of thickness coordinate. The theory inherently satisfies the zero transverse shear conditions on top and bottom surfaces of the plate. An eight-noded C0 continuous element is chosen by an adequate choice of nodal field variables. The governing equations are obtained for the free vibration and buckling responses of laminated-composite and sandwich plates. Intensive numerical experiments are conducted to investigate the influence of span-thickness ratio, boundary conditions, etc. on the free vibration and buckling behavior. The comparison of present results with the published results indicates the performance and range of applicability of the present theory in the framework of finite element analysis.

Methods for the Construction of the Kinetic Diagrams of Fatigue Fracture for Steels Under the Conditions of Trаnsverse Shear with Regard for the Friction of Crack Lips

We propose the design of a specimen for the investigation of the fatigue fracture of steels under trans- verse shear. A formula for the determination of the stress intensity factor with regard for the friction of crack lips is obtained with the use of the finite-element method. The methods aimed at the construction of the kinetic diagrams of fatigue fracture under the conditions of transverse shear are developed and tested on specimens of 65G structural steel. We plot the kinetic diagram of fatigue fracture and approx- imate its middle segment by a linear dependence in the established parameters. The life of structural elements with sharp concentrators operating the under conditions of shear stresses should be evaluated on the basis of the approaches of fatigue fracture mechanics under the conditions of trans- verse shear. This is why it is necessary to develop methodical recommendations for the reliable determination of the characteristics of cyclic crack resistance (CCCR) of the materials in transverse shear. In the case of mode I fatigue fracture of metallic materials, the methods aimed at the determination of the CCCR were standardized in (1). Some experimental investigations of the mode II fatigue fracture of steels based on the models neglecting the stage of stable growth of fatigue cracks or the friction of their lips are also known (2-5). This negatively affects the analysis of the stress-strain state (SSS) near the crack tip, the determi- nation of the CCCR of materials, and the evaluation of the service life of structural elements as a whole, which should be taken into account in the development of new methods for the construction of the kinetic diagram of fatigue fracture (KDFF) in transverse shear. The aim of the present work is to develop new methods for the construction of the KDFF and evaluation of the CCCR of steels in transverse shear with regard for the friction of crack lips.

Determination of the Parameters of Crack Resistance for 17g1s Steel Under Transverse Shear

We determine the static crack resistance of compact Richard’s specimens made of 17G1S steel and the critical crack opening displacement under the conditions of transverse shear (mode II). The specimens are tested under cyclic loading. Richard’s specimens are modernized with an aim to improve the conditions for the initiation and growth of mode II cracks. By using the digital image correlation method, we determine the distribution of strains near the notch tip.

Effect of Closure of a Crack Caused by the Roughness of Its Surfaces on Fatigue Fracture under the Conditions of Transverse Shear

We develop a model aimed at the prediction of propagation of mode II fatigue cracks with regard for the interaction of their lips caused by the roughness of the fracture surfaces. In this model, the relationship between normal and shear contact stresses is described by the Amonton's law of friction and the plastic yield of the material in the prefracture zone is taken into account with the help of the model of thin plastic strips. The method of singular integral equations is used to solve the corresponding boundary-value problem for a plate with cracks propagating from two semiinfinite collinear notches. The distribution of contact stresses is determined and the stress intensity factors and displacements of the crack lips are evaluated. The proposed example is used to analyze the basic specific features of the influence of contact of the crack lips on fatigue fracture under the action of shear loads. The obtained results are confirmed by the experimental data on the propagation of mode II fatigue cracks in specimens of HY-130 steel.

Contribution to the nonlinear theory of multilayered composite shells featuring damaged interfaces

Based on a displacement field which: (i) accounts for an arbitrary distribution of the tangential displacements through the shell thickness; (ii) fulfills a priori the continuity conditions on the transverse shear stresses at the interfaces between the layers; (iii) fulfills the zero transverse shear conditions on the top and bottom surfaces; and (iv) allows for jumps in the tangential displacements when interlayer slips are present, the equations governing the geometrically nonlinear elastodynamic behavior of multilayered composite shallow shells are derived by using the virtual work principle. First-order and third-order shallow shells models are obtained as special cases. The work is an extension of the multilayered composite shallow shells of a recently developed model for multilayered composite plates featuring damaged interfaces [AIAA J, 35(11) (1997) 1753].

Main crack in the field of microdefects in transverse shear conditions

1. We formulated the boundary conditions and presented a method of solving a problem of the interaction of a crack with a field of microcracks taking into account possible contact between the crack edges.