Interference fit effect on holed single plates loaded with tension-tension stresses

This paper deals with the influence of interference fit coupling on the fatigue strength of holed plates. The effect was investigated both experimentally and numerically. Axial fatigue tests have been carried out on holed specimens made of high performance steel (1075MPa of Ultimate strength and 990MPa of Yield strength) with or without a pin, made of the same material, press fitted into their central hole. Three different conditions have been investigated: free hole specimens, specimens with 0.6% of nominal specific interference and specimens with 2% of nominal specific interference. The experimental stress-life (S–N) curves pointed out an increased fatigue life of the interference fit specimens compared with the free hole ones. The numericalinvestigation was performed in order to analyse the stress fields by applying an elastic plastic 2D simulation witha commercial Finite Element software. The stress history and distribution along the contact interference of the fitted samples indicates a significant reduction of the local stress range due to the externally applied loading (remote stress) since a residual and compressive stress field is generated by the pin insertion

Interference fit effect on holed single plates loaded with tension-tension stresses

This paper deals with the influence of interference fit coupling on the fatigue strength of holed plates. The effect was investigated both experimentally and numerically. Axial fatigue tests have been carried out on holed specimens made of high performance steel (1075MPa of Ultimate strength and 990MPa of Yield strength) with or without a pin, made of the same material, press fitted into their central hole. Three different conditions have been investigated: free hole specimens, specimens with 0.6% of nominal specific interference and specimens with 2% of nominal specific interference. The experimental stress-life (S–N) curves pointed out an increased fatigue life of the interference fit specimens compared with the free hole ones. The numerical investigation was performed in order to analyse the stress fields by applying an elastic plastic 2D simulation with a commercial Finite Element software. The stress history and distribution along the contact interference of the fitted samples indicates a significant reduction of the local stress range due to the externally applied loading (remote stress) since a residual and compressive stress field is generated by the pin insertion

Characterization of anisotropic nano-particles by using depolarized dynamic light scattering in the near field

Light scattering techniques are widely used in many fields of condensed and sof t matter physics. Usually these methods are based on the study of the scattered light in the far field. Recently, a new family of near field detection schemes has been developed, mainly for the study of small angle light scattering. These techniques are based on the detection of the light intensity near to the sample, where light scattered at different directions overlaps but can be distinguished by Fourier transform analysis. Here we report for the first time data obtained with a dynamic near field scattering instrument, measuring both polarized and depolarized scattered light. Advantages of this procedure over the traditional far field detection include the immunity to stray light problems and the possibility to obtain a large number of statistical samples for many different wave vectors in a single instantaneous measurement. By using the proposed technique we have measured the translational and rotational diffusion coefficients of rod-like colloidal particles. The obtained data are in very good agreement with the data acquired with a traditional light scattering apparatus.Comment: Published in Optics Express. This version has changes in bibliograph

Nanoparticle characterization by using Tilted Laser Microscopy: back scattering measurement in near field

By using scattering in near field techniques, a microscope can be easily turned into a device measuring static and dynamic light scattering, very useful for the characterization of nanoparticle dispersions. Up to now, microscopy based techniques have been limited to forward scattering, up to a maximum of 30 degrees. In this paper we present a novel optical scheme that overcomes this limitation, extending the detection range to angles larger than 90 degrees (back-scattering). Our optical scheme is based on a microscope, a wide numerical aperture objective, and a laser illumination, with the collimated beam positioned at a large angle with respect to the optical axis of the objective (Tilted Laser Microscopy, TLM). We present here an extension of the theory for near field scattering, which usually applies only to paraxial scattering, to our strongly out-of-axis s ituation. We tested our instrument and our calculations with calibrated spherical nanoparticles of several different diameters, performing static and dynamic scattering measurements up to 110 degrees. The measured static spectra and decay times are compatible with the Mie theory and the diffusion coefficients provided by the Stokes-Einstein equation. The ability of performing backscattering measurements with this modified microscope opens the way to new applications of scattering in near field techniques to the measurement of systems with strongly angle dependent scattering.Comment: 18 pages, 10 figures. Accepted for publication in Optics Express, vol. 17, no. 17 (08/17/2009

Effect of different underhead shot-peening and lubrication conditions on high-strength screws undergoing multiple tightenings

This study investigates the effect of shot-peening on the bearing friction coefficient of 42CrMoV grade 14.9 screws. An experimental campaign was conducted on a tribological testing rig, investigating the combined effects of shot peening treatments, lubrication conditions, and number of tightenings on the frictional coefficient. A first set of tests was performed, considering the same shot-peening conditions as in a previous study to highlight the role of different material. A second campaign was carried out, adjusting the process parameters to enhance the tribological response. Small shots and high-impact energy are suitable for tightening with lubricant, whereas, in dry conditions, larger shots and lower-impact energy lead to particularly low friction coefficients that are well aligned to those achievable when using lubricants

Effects of infill temperature on the tensile properties and warping of 3D-printed polylactic acid

Although extensive research has been carried out on the effects of temperature on the properties of parts by fused filament fabrication, no study considered the opportunity to use different temperatures and cooling strategies for the contour and the infill region. The purpose of this investigation is to explore such an opportunity through an experimental campaign on polylactic acid. Specifically, the variations in tensile properties and warping occurring with different infill temperatures and cooling methods are documented. The results demonstrate that diversifying process parameters used for the contour and infill of the part allow for significant improvements in mechanical properties without affecting the distortion of the manufactured samples. This result can be achieved by either increasing the nozzle temperature or switching off the cooling fan during infilling

On the impact strength of adhesive bonded pin-and-collar joints

Nowadays, the adhesive technology is gaining relevance in industrial sectors where impact operating conditions are very common. At the same time, tests on cylindrical joints represent a well-established method for determining the static strength of structural adhesives. This work aims at assessing the impact properties of structural adhesives by means of cylindrical joints. The investigation involved two adhesive formulations (an epoxy resin and an anaerobic) and has been carried out under static, quasi-static and low-velocity impact conditions. The main outcomes of the work are: (i) the pin-collar specimen is well suited to analyzing the impact properties of adhesives; (ii) both adhesives showed a dependence of the strength and stiffness properties on the strain rate; (iii) the epoxy product showed a greater impact toughness than the anaerobic. In appendix, the authors report the tuning procedure of a CZM numerical model in a commercial FE package, based on the experimental results

Interference fit effect on holed single plates loaded with tension-tension stresses

This paper deals with the influence of interference fit coupling on the fatigue strength of holed plates. The effect was investigated both experimentally and numerically. Axial fatigue tests have been carried out on holed specimens made of high performance steel (1075MPa of Ultimate strength and 990MPa of Yield strength) with or without a pin, made of the same material, press fitted into their central hole. Three different conditions have been investigated: free hole specimens, specimens with 0.6% of nominal specific interference and specimens with 2% of nominal specific interference. The experimental stress-life (S–N) curves pointed out an increased fatigue life of the interference fit specimens compared with the free hole ones. The numericalinvestigation was performed in order to analyse the stress fields by applying an elastic plastic 2D simulation witha commercial Finite Element software. The stress history and distribution along the contact interference of the fitted samples indicates a significant reduction of the local stress range due to the externally applied loading (remote stress) since a residual and compressive stress field is generated by the pin insertion

Effect of the Position in the Build Chamber on the Fatigue Strength of Additively Manufactured Maraging Steel MS1

The quality of additively produced parts and the achievable mechanical response may be affected by several factors, such as build orientation, heat treatment, or machining. A further rarely investigated factor is the position of the built part in the chamber with respect to inert gas flow. Previous studies have highlighted that the interaction between gas flow and laser track may induce an intense vaporization with consequent lack of fusion, particle entrainment, drop in density and denudation of the produced part, which is likely to detrimentally affect mechanical properties. This study addresses the effect of part position on the fatigue strength of heat-treated maraging steel MS1 produced by an EOSINT M280 machine in a nitrogen environment. Novelty arises from the lack of studies in this field, especially under fatigue. A factorial plan with subsequent statistical analysis highlighted that positioning the part upstream with respect to the gas flow leads to a slightly lower fatigue strength; however, no significant differences are observed. The failure mode, involving initiation from subsurface porosities of the same size, is also unaffected. Finally, a fatigue limit of 26% of the ultimate tensile strength is found, which is consistent with previous outcomes

Design and Optimization of a Pneumatic Clamping System for Direct-Driven Rotary Tables

Modern direct-driven and high-speed rotary tables with torque motor are optimally suited for all handling and assembly applications that require the shortest indexing times and flexible positioning. The following paper is devoted to the study, the design, and the optimization of an innovative table clamping system (brake for accurate positioning) actuated by pneumatic energy, working at a maximum clamping pressure of 6 bar. The challenge for the aforementioned application is related to developing a solution able to provide a maximum tangential torque (with clamping actuated) in the range of thousands of Nm without leveraging the use of high-pressure hydraulic energy. The optimization of the proposed solution is based on the precise calculation of the stresses in order to perform a fatigue assessment and on the elastic deformation of the clamps in order to set the correct tolerances between the mating parts. Eventually, an experimental campaign is carried out in order to tune the numerical model, which is then used to validate the proposed design solution