A revised method to calculate time-varying mesh stiffness of helical gear

Time-varying mesh stiffness (TVMS) of gear plays vital role in analysing dynamic characteristic of gear transmission. So accurately evaluating the TVMS is important and essential. In this paper, a revised method to calculate the TVMS of helical gear is proposed. Based on slice method, the helical gear is sliced into pieces along the tooth width direction. The proposed method corrects the fillet foundation stiffness within multi-tooth in contact and considers the non-linearity and load-dependence of the Hertzian contact stiffness. The effect of the axial mesh force is considered. Finally, an equivalent helical gear model is established in ANSYS to study the mesh stiffness. The results show the proposed method has high effectiveness compared with FEM (finite element method).

Technical solution for evaluation of contact stiffness and strength of the joint surfaces of injector

От работоспособности форсунки зависит качество работы двигателя, его долговечность, соответствие экологическим нормам и требованиям, а от контактной прочности, жесткости и работоспособности ее сопрягаемых поверхностей (различных соединений, которые можно отнести к условно-неподвижным) – нормальная эксплуатация рассматриваемой конструкции в целом. На базе существующей технологии производства форсунок и с использованием физико-математической модели упругопластического контактирования, созданной авторами, предложено техническое решение для оценки контактной жесткости и прочности стыковых поверхностей форсунки для распыления топлива. Авторами установлено, что работа двигателя в целом зависит от характеристик контактирующих поверхностей форсунки, а именно параметров микрогеометрии шероховатого слоя, фактической площади соприкосновения, податливости, физико-механических свойств материалов контактной пары, условий нагружения. На основе проведенных авторами исследований и комплексного анализа при заданных геометрических размерах конструкции форсунки двигателя внутреннего сгорания и условий работы ДВС разработано техническое решение, позволяющее повысить контактную жесткость стыковых сопряжений форсунки для распыления топлива и равномерного его распределения в камере сгорания дизеля в 1,2–1,5 раза. Таким образом, предлагаемое авторами решение показало свою эффективность, и его можно рекомендовать для применения в ДВС, в том числе в судовых двигателях.

Analytical Solution for Circular Tunnel under Obliquely Incident P Waves considering Different Contact Conditions

An analytical solution for the seismic-induced thrust and moment of the circular tunnel in half-space under obliquely incident P waves is developed in this study, which is the superposition of the solution for deep tunnels under incident and reflected P waves and the reflected SV waves. To consider tangential contact stiffness at the ground-tunnel interface, a spring-type stiffness coefficient is introduced into the force-displacement relationship. Moreover, the tunnel lining is treated as the thick-wall cylinder, providing more precise forecasts than beam or shell models used in previous analytical solution, especially for tunnels with thick lining. The reliability of the proposed analytical solution is assessed by comparing with the dynamic numerical results. Based on the proposed analytical solution, parametrical studies are conducted to investigate the effect of some critical factors on the tunnel’s seismic response, including the incident angles, the tangential contact stiffness at the ground-tunnel interface, and the relative stiffness between the ground and the tunnel. The results demonstrate that the proposed analytical solution performs well and can be adopted to predict the internal forces of circular tunnels under obliquely incident P waves in seismic design.

Static and Impact Response of a Single-Span Stone Masonry Arch

Unreinforced masonry structures are susceptible to man-made hazards such as impact and blast loading. However, the literature on this subject mainly focuses on masonry wall behavior, and there is a knowledge gap about the behavior of masonry arches under high-strain loading. In this context, this research aims to investigate both quasistatic and impact response of a dry-joint stone masonry arch using the discrete element method. Rigid blocks with noncohesive joint models are adopted to simulate dry-joint assemblages. First, the employed modeling strategy is validated utilizing the available experimental findings, and then sensitivity analyses are performed for both static and impact loading, considering the effect of joint friction angle, contact stiffness, and damping parameters. The outcomes of this research strengthen the existing knowledge in the literature regarding the computational modeling of masonry structures that are subjected to usual and extreme loading conditions. The results highlight that applied discontinuum-based numerical models are more sensitive to stiffness parameters in high-strain loading than static analysis.

Extended characterization of materials based on continuous instrumented indentation diagrams

In addition to the traditional determination of hardness and elastic moduli from continuous diagrams of instrumental indentation, it is proposed to determine the yield stress, the characteristic of plasticity, the characteristic relative size of the elastoplastic zone under the indenter, and the volumetric deformation of the material in the area of contact of the indenter with the sample. The indentation diagram shows the transition point to the unconstrained material flow under the indenter. Keywords: indentation, hardness, elastic moduli, contact stiffness, elastic-plastic strains.

Three-Dimensional Finite Element Analysis of Contact Problem in Dry Friction Clutches

We present an investigation through numerical analysis (FEM) of the solution of the contact problem in friction clutch systems during engagement manoeuver. The case of high contact pressure between the sliding elements of a clutch system (flywheel, friction clutch and pressure plate) has been also considered. A finite element model of a dry friction clutch system (single disc) to estimate the distributions of the contact pressure between the contact elements of the clutch system under different working conditions has been developed and the main findings are discussed. Furthermore, the effect of modules of elasticity (contact stiffness) on the distribution of contact pressure of the mating surfaces was investigated. Also, the results encompass the deformations of the contacting surfaces for different cases. This work could provide a fundamental intermediate step to obtain a partial solution to the thermos-elastic problem in order to compute the thermal-driven deformations and stresses in the automotive clutches and brakes under different working conditions.

Poor bone quality in patients with rheumatoid arthritis receiving long-term bisphosphonate therapy for glucocorticoid-induced osteoporosis: an iliac bone biopsy study

Background Bisphosphonates (BPs) have been shown to reduce the incidence of vertebral fractures during the first year or two of glucocorticoid (GC) treatments and are therefore recommended as a first-line treatment for the prevention and treatment of GC-induced osteoporosis (GIO). However, there are theoretical concerns about the long-term use of BPs in low-turnover osteoporosis caused by chronic GC therapy. Methods We analyzed the trabecular microarchitecture, bone metabolism, and material strength of bone biopsy samples from the iliac crest of female patients with rheumatoid arthritis (RA) receiving an average of 6.7 years of BP therapy for GIO (GIOBP group, n = 10), compared with those of age- and bone mineral density (BMD)-matched non-RA postmenopausal women with no history of anti-osteoporosis medication use (reference group, n=10). Results Patients in the GIOBP group had a significantly greater fracture severity index, as calculated by the sum of the Genant visual semiquantitative grading scores of vertebral fractures (T4-L5) compared with the reference patients. Micro-computed tomography analysis showed that the degree of mineralization and trabecular microarchitecture were significantly lower in the GIOBP group than in the BMD-matched reference patients. Patients in the GIOBP group exhibited lower bone contact stiffness, determined by micro-indentation testing, than in the reference group. The contact stiffness of the bone was negatively correlated with the fracture severity index and the daily prednisolone dosage. Immunohistochemistry and serum bone turnover markers showed decreased osteoclastic activity, impaired mineralization, and an increased fraction of empty lacunae in the GIOBP group. Conclusions Our findings indicate that patients with RA receiving long-term BP for GIO are still at high risk for fragility fractures because of poor bone quality.