A Data-Driven Method for Predicting Deformation of Machined Parts Using Sparse Monitored Deformation Data

In the aircraft industry, where high precision geometric control is vital, unexpected component deformation, due to the release of internal residual stress, can limit geometric accuracy and presents process control challenges. Prediction of component deformation is necessary so that corrective control strategy can be defined. However, existing prediction methods, that are mainly based on the prediction or measurement of residual stress, are limited and accurate deformation prediction is still a research challenge. To address this issue, this paper presents a data-driven method for deformation prediction based on the use of in-process monitored deformation data. Deformation, which is caused by an unbalanced internal residual stress field, can be accurately monitored during the machining process via an instrumented fixture device. The state of the internal stress field within the part is first estimated by the using the part deformation data collected during machining process, and then, the deformation caused by a subsequent machining process is predicted. Deep learning is used to establish the estimating module and predicting module. The estimating module is used to infer the unobservable residual stress field as vectors by using sparse deformation data. The inferred vector is then used to predict the deformation in the predicting module. The proposed method provides an effective way to predict deformation during the machining of monolithic components, which is demonstrated experimentally.

Width Design of Small Coal Pillar of Gob-Side Entry Driving in Soft Rock Working Face and Its Application of Zaoquan Coal Mine

Reasonable width of gob-side coal pillar can reduce the waste of coal resources and is conducive to roadway stability. According to the distribution of internal and external stress fields at the working face, a method for determining the width of gob-side coal pillar was proposed. The coal pillar and roadway should be set within the internal stress field, and support is provided through the anchored part and the intact part of the coal pillar. The method was used in the design of the coal pillar at No. 130205 working face of Zaoquan Coal Mine. The calculation results indicated that the width of a coal pillar suitable for gob-side entry is 6.0 m. It is reasonable to arrange the roadway and coal pillar in the low-stress zone with a width of 11 m. During tunnelling of roadway and stoping of the working face, the deformation of the roadway increased with a reduction in the distance from the working face. Even during stoping of the working face, there was an approximately 1.5 m intact zone in the coal pillar. This indicates that the proposed method of designing small coal pillar of gob-side entry driving is reliable.

ANALYSIS OF LOCAL FIELDS OF ELASTIC STRESS GENERATED BY ROTATIONAL-SHEAR MESODEFECTS NEAR THE JUNCTIONS OF GRAINS

The work is devoted to the study of the structure of the elastic stress field in the area of junctions of grain boundaries containing strain-induced rotational-shear mesodefects. The jumps in plastic distortion of grains when passing through grain boundaries create additional misorientations on them, the mismatch of which at the junctions of grains leads to the appearance of linear mesodefects of the rotational type – junction disclinations. Planar mesodefects of the shear type appear on the flat sections of the boundaries, which are plastic shears uniformly distributed along the boundaries. These mesodefects create spatially inhomogeneous elastic stress fields near the junctions and ledges of the grains. They increase during plastic deformation and, at sufficiently large value of strain, initiate the formation of a fragmented material structure. Rotational-shear mesodefects are also the cause of the nucleation and accumulation of microcracks at the stage of viscous fracture of polycrystalline solids. In this work, asymptotic formulas are obtained that make it possible to analyze the distribution and anisotropy of the internal stress field in the vicinity of the grain junction from rotational-shear mesodefects. It was found that the components of the stress field weakly depend (logarithmically) on the length of the grain boundaries formatting junction of the grains. It is shown that the screening disclination of the dipole leads to the appearance of an angular dependence of the diagonal components of the elastic stress tensor in the vicinity of the junctions and its contribution to the elastic field of the disclinations dipole is about 10–15%. The obtained asymptotic expressions can be used to study the kinetics of a dislocation ensemble and to analyze the conditions for the nucleation of microcracks in the vicinity of joints and ledges of grains.

FEA Modelling of the Combined Hard TurningRolling Process Used at Bearing Rings

In general, the production of bearings is a very large series production, which is why in production the technological lines are designed to process a single size of bearings. Changing the production line for different types of bearings is expensive and time consuming, especially where grinding and honing processes are required. An alternative to these abrasive processes is hard turning. The literature indicates that due to highprecision machines, the accuracy of hard-turned parts is comparable to grinding processes. It is also indicated that the integrity of the surface and the topography of the surface together with the residual induced stresses are parameters of interest and that influence the performance of the bearings. So one method of increasing the durability of the bearings is to ensure a low roughness of the elements and high residual induced stresses. Deep rolling is considered as an alternative to honing and rectification processes. Rolling can induce higher surface stresses in the material compared to honing and grinding. The present paper proposes a combined cutting tool made of a hard turning head and a rolling cutting tool for machining bearing rings. A simulation of this combined process is performed with the help of the finite element and thus the internal stress field, the temperature fieldand the topography of the processed surface aredetermined.

Uniformity of stresses inside a non-elliptical inhomogeneity interacting with a mode III crack

Using conformal mapping techniques and the theory of Cauchy singular integral equations, we prove that it is possible to maintain a uniform internal stress field inside a non-elliptical elastic inhomogeneity embedded in an infinite matrix subjected to uniform remote stress despite the fact that the inhomogeneity interacts with a finite mode III crack. The crack can be modelled either as a Griffith crack or as a Zener–Stroh crack. Our analysis further indicates that the existence of the crack plays a key role in influencing the shape of the corresponding inhomogeneity but not the internal uniform stress field inside the inhomogeneity. Numerical examples are presented to demonstrate the solution.

Continuous Modeling of Dislocation Cores Using a Mechanical Theory of Dislocation Fields

A one-dimensional model of an elasto-plastic theory of dislocation fields is developed to model planar dislocation core structures. This theory is based on the evolution of polar dislocation densities. The motion of dislocations is accounted for by a dislocation density transport equation where dislocation velocities derive from Peach-Koehler type driving forces. Initial narrow dislocation cores are shown to spread out by transport under their own internal stress field and no relaxed configuration is found. A restoring stress of the lattice is necessary to stop this infinite relaxation and it is derived from periodic sinusoidal energy of the crystal. When using the Peierls sinusoidal potential, a compact equilibrium core configuration corresponding to the Peierls analytical solution is obtained. The model is then extended to use generalized planar stacking fault energies as an input and is applied to the determination of properties of planar dislocation cores in crystalline materials. Dissociations of edge and screw dislocation cores in basal and prismatic planes of Zirconium are shown.