A modified X-ray diffraction method to measure residual normal and shear stresses of machined surfaces

X-ray diffraction has been widely used in measuring surface residual stresses. A drawback of the conventional d ~ sin2ψ method is the increased uncertainty arising from sin2ψ splitting when a significant residual shear stress co-exists with a residual normal stress. In particular, the conventional method can only be applied to measure the residual normal stress while leaving the residual shear stress unknown. In this paper, we propose a new approach to make simultaneous measurement of both residual normal and shear stresses. Theoretical development of the new approach is described in detail, which includes two linear regressions, $$\frac{{d}_{\psi }+ {d}_{-\psi }}{2}$$ d ψ + d - ψ 2 ~sin2ψ and {dψ-d-ψ} ~ sin(2ψ), to determine the residual normal and shear stresses separately. Several samples were employed to demonstrate the new method, including turning-machined and grinding-machined cylindrical bars of a high strength steel as well as a flat sample of magnetron sputtered TiN coating. The machined samples were determined to have residual compressive normal stresses at both the axial and hoop directions as well as various scales of residual shear stresses. The TiN coating showed a high scale of residual compressive (normal) stress whereas the measured residual shear stress was extremely low. The new method showed significantly increased precision as compared to the conventional d ~ sin2ψ method.

MODELING OF SCHEMES OF CRACK DEVELOPMENT IN SHAPE SHELLS BASED ON TRAJECTORIES OF THE LARGEST TENSION STRESS

В статье для пологой оболочки, загруженной равномерно распределенной нагрузкой, со схемой опирания на шарнирные опоры получено аналитическое решение. Нагрузка и неизвестные функции прогиба и напряжений представлены с помощью двойных тригонометрических рядов. Выполнены расчеты напряженно-деформированного состояния, определены усилия и перемещения. Дана оценка точности суммирования рядов по перемещениям и усилиям. В окрестности точек нижней, срединной и верхней поверхностей оболочки вычислены нормальные и касательные напряжения, а также главные напряжения и главные площадки. Показана картина двухосного напряженного состояния и на ее основе построены графики траекторий наибольших растягивающих напряжений. Графики траекторий на нижней поверхности оболочки сопоставлены с экспериментальными схемами развития трещин. По траекториям наибольших растягивающих напряжений, построенных в точках нижней поверхности, делается прогноз о месте, направлении и последовательности появления трещин в оболочке. An analytical solution is obtained in the article for a shallow shell loaded with a uniformly distributed load, with a scheme of bearing on hinged supports. Load and unknown deflection and stress functions are represented using double trigonometric series. Calculations of the stress-strain state were performed, forces and displacements were determined. An assessment of the accuracy of summation of the series of displacements and efforts is given. In the vicinity of the points of the lower, middle and upper surfaces of the shell, normal and shear stresses, as well as principal stresses and principal areas, are calculated. The picture of the biaxial stress state is shown and on its basis, the graphs of the trajectories of the highest tensile stresses are constructed. The trajectory plots on the lower surface of the shell are compared with the experimental crack propagation schemes. The trajectories of the highest tensile stresses plotted at the points of the lower surface are used to predict the location, direction, and sequence of cracks in the shell.

Fatigue Damage Map of AZ31B-F Magnesium Alloys under Multiaxial Loading Conditions

In this work, the mechanical behavior of the AZ31B-F magnesium alloy under cyclic loading is analyzed with the goal of contributing to the advancement of its use in the design of AZ31B-F components and structures. To achieve this goal, an experimental program was implemented to evaluate the cyclic response of the AZ31B-F under specific proportional loads with different stress amplitude ratios. Afterwards, regression methods were applied to extend the experimental data to a wide range of proportional loads. As a result, the AZ31B-F damage map, a material property that stablishes the damage scale between normal and shear stresses for finite life loading regimes, was obtained. In addition, a safety factor was developed for the AZ31B-F material when subjected to proportional loading. The achieved results have a direct application in mechanical design of components/structures made of AZ31B-F contributing to its reliability.

THE RIGIDITY OF THE EXTERNAL WALL PANEL WITH OPENING OF RESIDENTIAL BUILDING I-515/5 SERIES IN CASE BIAS

There were a number of characteristic damages and defects in typical panel houses when examine, one of which are tilts and biases of wall panels. The stiffness of the wall panel with the opening of residential building I-515/5 series has been determined at a given bias in its plane. The panel was calculated numerically using a nonlinear deformation model by the finite element method and analytically. The software package, LIRA-SAPR 2017, was used in this investigation. The calculation was carried out taking into account the nonlinearity and material creep. As a result, the fields of normal and shear stresses in the panel were obtained and the shear rigidity was calculated. The analysis of the obtained results showed that a possible decrease of the actual stiffness of the panel should take into account against the calculated stiffness was obtained according to the standards.

Anisotropy Effect of Masonry on the Behaviour and Bearing Capacity of Masonry Walls

Firstly, an updated numerical model for the numerical analysis of planar unreinforced and confined masonry walls is presented. The model can simulate the main nonlinear material effects of masonry and reinforced concrete. A simplified anisotropic constitutive model for masonry is developed and presented. The criteria for the limit bearing capacity and collapse of masonry are separately defined for normal stresses only and for normal and shear stresses. The presented numerical model is verified and used to analyse the anisotropy effect of masonry on the behaviour of unreinforced and confined two-story anisotropic masonry walls with different coefficients of anisotropy, wall lengths, and quality of masonry under horizontal static forces. The influence of the anisotropy coefficient of the masonry on the response of the walls is discussed in detail, and the main conclusions are given.

Failure conditions of solid wood on off-axis compression testing

Off-axis compression tests (OACT) were conducted on solid wood from six tree species, and the relationship between the off-axis compressive strength (OACStr) and the off-axis angle was predicted under the conventional Hill-type quadratic failure conditions, off-axis special failure conditions, and under a condition proposed in this study, which contains terms of interaction between the normal and shear stresses. The latter was an effective approach for accurately predicting the OACStr, although the physical meaning of the interaction terms is not yet clear. Under the off-axis specialized conditions, the approach was simple and accurate for predicting the OACStr, which includes the 45° off-axis angle.