Operational control of the strength of safety parts limiting ultimate loads

A non-destructive method for determining the shear strength of parts based on the laws of elastoplastic penetration of an indenter into a test material is considered. Experiments confirmed the effectiveness of the method in practice. Keywords: non-destructive method, shear strength, elastoplastic contact, plastic hardness. [email protected]

Normal fractal contact stiffness model among three disks of rod-fastening rotor system with considering friction and the asperities interaction

Purpose The purpose of this study is to develop a normal contact stiffness (NCS) model among three disks of the assembled rotor system, which systematically considers the friction coefficient, the asperities interaction and the elastoplastic contact regime. Design/methodology/approach Based on the revised fractal theory, considering the friction effect, the elastoplastic contact regime and the asperities interaction in a simple way, the total NCS among three disks of the rod-fastening rotor bearing system is established. Effects of fractal dimension and roughness, friction coefficient, asperities interaction and material properties on the normal stiffness are investigated by simulations and the relevant comparisons are given for examining the reasonability of the proposed model. Findings NCS will decrease when asperities interaction and friction are included. As the load increases, the influences of asperities interaction and friction on stiffness become serious. NCS will be enhanced when the elastoplastic regime is considered. Originality/value A comprehensive NCS model is developed. It provides a theoretical basis for the modeling of the NCS for multi-interfaces.

Three-Dimensional Elastoplastic Contact Analysis of Rough Surface Considering a Micro-Scale Effect

The micro-surface asperity scale of grinding metal parts is within several microns. When two grinding surfaces are in contact, the unevenness of the plastic deformation of the asperities at the micro-scale leads to greater plastic hardening strength of the material. The results of the nano-indentation experiment conducted in this paper confirmed this phenomenon. Based on conventional mechanism-based strain gradient (CMSG) plasticity theory, the micro-scale plastic constitutive equation of materials is given and then is verified by the nano-indentation experiment. Finite element software abaqus and the user-defined element (UEL) subroutine are used to build three-dimensional rough surface elastoplastic contact models. By calculating the grinding rough surface contact in the macro-scale constitutive model based on J2 theory and in the CMSG plasticity constitutive model, the influence law of plastic micro-scale effect on contact performance is obtained.

Validation of the Model of Elastoplastic Contact of Spiroid Gears

The paper considers the problem of analyzing the elastoplastic contact of teeth in a heavy-loaded low-speed multi-pair spiroid gear. This problem is an integral part of the strength analysis that enables forecasting the load-carrying capacity of the product at the initial stage of its development. The relevance of the considered method and algorithm of calculating the load distribution and plastic strain of teeth is emphasized by its increased productive efficiency as compared to the widely used finite element method. The paper considers a common issue of validation of the developed algorithm, i.e. the correspondence of the obtained solution to the results of a real loading process. The main steps of the algorithm are given with account of the multi-pair contact and macro-roughnesses on the contact flanks that are represented as the set of areas (cells). The coordinates of the cell centers are calculated taking account of the factors influencing the load distribution in the spiroid gearing, such as manufacturing and/or assembly errors, surface micro- and macro-roughnesses, and deformations of the gearbox parts. To validate the algorithm, only one dominating factor — the gearwheel surface undulation — is chosen, since all the other factors are negligibly small. The object of the study is a gear in one of the mass-produced multi-turn spiroid gearboxes for pipeline valves. The criteria for the algorithm validation are formulated, namely, the plastic strain value, the area, shape and arrangement of the pattern of the plastic strain. By analyzing the results of numerical and experimental modeling it is possible to draw a conclusion on the validity of the results obtained by means of the studied numerical method of analysis. The divergence of the plastic strain value obtained experimentally and through calculation was under 10%, and the area of the plastic strain pattern was under 10%.

Stiffness model of fixed joint considering self-affinity and elastoplasticity of asperities

Purpose The purpose of this paper is to establish a stiffness model of fixed joint considering self-affinity and elastoplasticity of asperities. Design/methodology/approach The proposed model considers that asperities of different scales are interrelated rather than independent. For elastoplastic contact, a spring-damper model and an elastic deformation ratio function were proposed to calculate the contact stiffness of asperities. Findings A revised fractal asperity model was proposed to calculate the contact stiffness of fixed joint, the impacts of the fractal dimension, the fractal roughness parameter and the Meyer index on the contact stiffness were discussed, and the present experimental results and the Jiang’s experimental results showed that the stiffness can be well predicted by proposed model. Originality/value The contradiction between the Majumdar and Bhushan model and the Morag and Etsion model can be well explained by considering the interaction among asperities of different scales. For elastoplastic contact, elastic deformation ratio should be considered, and the stiffness of asperities increases first and then decreases with the increasing of interference.