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The strength of a shaft-hub hybrid joint is affected by several factors, such as working temperature, interference level and coupling procedure. The first part of this study deals with temperature effect on the static response of shaft-hub hybrid joints. LOCTITE 648 anaerobic adhesive was applied for coupling 42CrMo4 tempered steel shafts to 16CrNi4Pb hardening steel hubs. The performance up to 100°C was experimentally investigated, involving press-fitted as well as shrink-fitted joints with interference up to 0.2%. Adhesive stripping upon coupling, adhesive degradation at high temperature and also frictional contribution decrease were highlighted. Afterwards, in the second part, the question of the adhesive being teared off under high interference was tackled. A hoop-channeled geometry was proposed, to increase the amount of adhesive remaining trapped at the joint interface. Hoop channels in the shafts proved to act as adhesive reservoir, thus facilitating adhesive dragging over the entire engagement length. Their effects on the joint strength were experimentally determined for both press-fitting and shrink-fitting coupling methods. The results, processed by the statistical tools of Analysis of Variance, orthogonality and pairwise tests, indicate the modified geometry is significantly beneficial for high interference press-fitted joints. Conversely, it may even be detrimental for shrink-fitted ones. [ABSTRACT FROM AUTHOR]

To prevent the preload loss, threadlockers are frequently used in threaded connections (e.g. to avoid self-loosening). Threadlockers are generally anaerobic adhesives and are commercially available either as semi-solid (pre-applied) or as liquid (to be applied just before tightening). Previous research deals with the frictional behavior of threaded joints with applied threadlocker. However, fasteners with applied threadlocker may sometimes operate at variable levels of temperature and humidity. A literature survey indicates there is a lack of data about the strength of joints with added threadlocker when they operate at different temperature/humidity levels with respect to conventional environmental conditions. In this research, the aforementioned issue has been tackled by means of an experimental campaign performed on liquid medium/high strength anaerobic adhesives (respectively, Loctite 243 and Loctite 270) applied to M10, 8.8 grade, zinc-coated screws. Following complete adhesive polymerization, the joints were aged in an environmental chamber, accounting for four combinations of temperature (room temperature – 90°C) and humidity (20–90%) for one week. The joints were then untightened, sampling the breakaway torque. Statistical analyses of the data were carried out, to assess the influence of each parameter on the breakaway torque of the aged joint, thus deriving useful data for design. [ABSTRACT FROM AUTHOR]

This paper focuses on cross-section optimization of both rectilinear and curvilinear beams. In particular, analytical models were developed, in order to detect how circular section resistance can be modified following a suitable cut. In fact, removing material from the furthest zone from the neutral axis, may even result in an increase of the section resistance modulus, with consequent beneficial reduction of the maximum stresses. The analytical model outcomes were confirmed by numerical analyses. This study deals with several applicative cases: in almost all of them a stress reduction was achieved, except for removing material from the extrados. [ABSTRACT FROM AUTHOR]

This study aims at developing an experimental tool useful to define accurately the friction coefficients in bolted joints and, therefore, at relating precisely the tightening torque to the bolt preloading force in some special components used in front motorbike suspensions. The components under investigation are some clamped joints made of aluminium alloy. The preloading force is achieved by applying a torque wrench to the bolt head. Some specific specimens have been appropriately designed and realized in order to study the tribological aspects of the tightening phase. Experimental tests have been performed by applying the Design of Experiment (DOE) method in order to obtain a mathematical model for the friction coefficients. Three replicas of a full factorial DOE at two levels for each variable have been carried out. The levels include cast versus forged aluminium alloy, anodized versus spray-painted surface, lubricated versus unlubricated screw, and first tightening (fresh unspoiled surfaces) versus sixth tightening (spoiled surfaces). The study considers M8x1.25 8.8 galvanized screws.

Clamped joints are shaft-hub connections used, as an instance, in front motorbike suspensions to lock the steering plates with the legs and the legs with the wheel pin, by means of one or two bolts. The preloading force, produced during the tightening process, should be evaluated accurately, since it must lock safely the shaft, without overcoming the yielding point of the hub. Firstly, friction coefficients have been evaluated on “ad-hoc designed” specimens, by applying the Design of Experiment approach: the applied tightening torque has been precisely related to the imposed preloading force. Then, the tensile state of clamps have been evaluated both via FEM and by leveraging some design formulae proposed by the Authors as function of the preloading force and of the clamp geometry. Finally, the results have been compared to those given by some strain gauges applied on the tested clamps: the discrepancies between numerical analyses, the design formulae and the experimental results remains under a threshold of 10%.

The aim of this research is to study the effect of the interference level and of the coupling procedure on the shear strength of Loctite 648 anaerobic adhesive. The tests involved shaft-hub joints with a quite large interference range and joined by a broad range of coupling strategies, which is one of the main issues of novelty of this research. 42CrMo4 tempered steel shaft specimens and 16CrNi4Pb hardening steel hub samples were used. Two factors were considered: the interference level and the assembly strategy. Four different levels of specific interference were analyzed up to a maximum value of 0.22%, performing five replications per level. Experimental trials were carried out with different coupling procedures: using press-fitted and shrink-fitted joints. Using the first procedure, a high level of interference induces scratches on the sample surfaces. These are conversely not produced by shrink-fitting. Some tests were devoted to friction coefficient estimation, thus also assessing the lubricating properties of the adhesive. Particularly, dry couplings and couplings and de-couplings with not yet cured adhesive were run to address this point. The results were processed by statistical methods, to assess the influence of the studied factors on the adhesive strength. [ABSTRACT FROM AUTHOR]

Threaded joints are widely used in the automotive industry, where threadlockers can be applied to prevent self-loosening and to possibly achieve a friction drop upon tightening. This study deals with this topic, investigating threadlocker tribological response before polymerization takes place. These lubricating properties are usually not considered in adhesive datasheets, but can be highly beneficial from the point of view of the achievable preload, thus preventing self-loosening. The topic was tackled experimentally, running an extensive campaign that involved a medium and a strong threadlocker (LOCTITE 243 and LOCTITE 270, respectively), used for tightening zinc-plated and black-oxidized screws. The testing procedure was inspired by a protocol being used by most manufacturers in the automotive field: in particular, the impacts of pre-tightening speed and of the time interval between pre-tightening and final tightening were investigated. The retrieved results indicate a lubricating effect of the medium threadlocker with achievable friction coefficients in the order of 0.11. Moreover, for both the threadlockers, a generally decreasing trend for the thread friction upon tightening for increasing time interval before tightening was observed. This is a particularly original outcome that could have remarkable implications for optimizing the assembly tasks of large sets of bolts. [ABSTRACT FROM AUTHOR]

This article focuses on the static structural analysis of a tibial intramedullary nail, carried out by the finite element method. The investigated subject is concerned with the issue of frictional contacts that, generating a non-linear problem, play an important role in numerical analyses. Experimental tests were also developed on tibial intramedullary nail specimens. The experimental results, in terms of force–displacement, were used to calibrate and validate the finite element analysis, by tuning the contact parameters available in the software. [ABSTRACT FROM AUTHOR]

The present paper deals with the structural analysis and the re-design of a cutting head for an automatic crosscutting machine. The machine is already marketed, and can process rectangular section wooden slats. The principal goal of this work is to develop a new mechanism capable of enhancing the productivity of the machine by around 80%. The work has been carried out by means of both numerical finite element analysis tools and analytical models. In fact, a secondary aim of the research is to define an analytical model which can capture the dynamic behavior of the device: this tool will be helpful to the design engineer in order to save costs associated with the development of future head designs. [ABSTRACT FROM AUTHOR]