Massimiliano De Agostinis

Normalization of the stress concentrations at the rounded edges of a shaft–hub interference fit: extension to the case of a hollow shaft

This work addresses the issue of stress concentrations at the rounded edges of shaft–hub interference fits. An infinitely long shaft, press fitted into a hollow hub with bore rounded edges is examined. Limited to interference fits involving a solid shaft, Strozzi and colleagues introduced a normalizing parameter, which accounts for the combined effects on the stress concentrations of the fillet radius, the shaft external radius and the interference level. The aim of this work is to extend the field of application of the said normalizing parameter, to the case of interference fits involving a hollow shaft. By means of finite element analysis, run-on geometries with different hub and shaft aspect ratios (ratio between internal and external diameters), charts for stress concentration factors as functions of the normalizing parameter were drawn. Appropriate functions are proposed, which allow obtaining the stress concentration factors valid for the case of hollow shaft, starting from the stress concentration factors valid for the case of solid shaft. The stress concentration factors predicted by means of this novel method are then compared with those provided by finite element analysis. Stress concentration factors in the presence of hollow shafts are demonstrated to be always higher than those evaluated for solid shafts. Finally, a numerical example illustrates the typical workflow to be followed in order to calculate the stress concentration factor for a defined joint.

Analysis of the Stress State in Brake Caliper Mounts of Front Motorbike Suspensions

The aim of this work is to analyze the stress and the strain fields in the brake caliper mounts of front motorbike suspensions produced by the braking action. First of all, some formulae useful to evaluate the maximum braking force in function of the vehicle features (e.g., total mass, centre of gravity position, tyre dimension, and brake disk diameter) have been developed. A mathematical model useful to calculate the axial, the bending, and the torque stresses on the braking caliper mounts has been then defined. The model has been developed by comparing the theoretical results with those obtained by some numerical analyses, based on the finite element method. An ad hoc test equipment has been, finally, designed and manufactured in order to define and analyze experimentally the strength of different types of brake caliper mounts and, at the same time, to verify the proposed model.

Fatigue Life Improvement of Holed Plates Made of an Innovative Medium C Micro-Alloyed Steel by Local Plastic Deformation

This paper deals with the influence of local plastic deformation on the fatigue strength of holed plates manufactured with an innovative medium-carbon micro-alloyed steel with high silicon content (hi-Si MCM). Local deformation around the hole is achieved by means of an interference fitted pin. The effect was investigated both experimentally and numerically. Microstructural characterization, hardness, and tensile tests were carried out first. Tension–tension fatigue tests were performed under two different conditions: open-hole (OH) specimens and specimens with a press fitted pin with 0.6% nominal specific interference. A 2D elastic–plastic finite element analyses (FEAs) investigation was done as well, in order to analyze the stress field in the vicinity of the hole. The stress history and distribution in the neighborhood of the hole indicate a significant reduction of the stress amplitude produced by the external loading (remote stress) when a residual stress field is generated by the pin insertion. In fact, experimental stress-life (SN) curves pointed out increased fatigue strength of the interference fit specimens, compared with the OH ones. Finally, scanning electron microscope (SEM) analyses of the fractured fatigue specimens were carried out, in order to investigate the mechanisms of failure and to relate them to the peculiar microstructural features that characterize this innovative steel.

The Rear Suspension Equilibrium

This chapter aims at defining the equations that govern the rear suspension in term of the overall equilibrium and loads applied for different conditions of the motorbike motion. The formulae are useful for designing a rear suspension made by a unique arm which connects the frame pin with the wheel axle. The equations are non-linear and implicit so that they can be solved by recursive methods applicable in a calc sheet. The mathematical models can be applied to different types of rear suspension but they are developed for the peculiar case of those equipped with an articulated mechanism which leads to a progressive stiffness of a single arm rear suspension.

A user-friendly computational algorithm for the structural analysis of wrapping machine rotating rings

Wrapping machines usually consist of a two- or a four-column frame, supporting a huge rotating ring, connected to a pre-stretch unit with film coil carrier. Stiffness is a key point of packaging machines, since it is strictly related to the accuracy of the wrapping task. It depends on the stiffness of the frame, which can be achieved by the four-column architecture, and on the ring constraint system. As a consequence, the ring structures are usually highly statically indeterminate. Nowadays, there is an increasing demand for higher rotational speeds and more reduced operation times. Therefore, an accurate structural analysis of the ring, considering its actual loading and constraints is more and more important. The structural analysis of the rotating ring is treated by many references; however, such a statically indeterminate constraining makes this problem highly complicated. The goal of this paper consists in the development of a general and original computational algorithm for the structural analysis of rotating rings. The results are collected in a user-friendly way in terms of normalized internal loads, so that they can be of a great help even for not expert users. This model has been experimentally validated and easily applied to case studies and optimization tasks.

Re-design of a uniplanar, monolateral external fixator

This work deals with the structural analysis of screw clamps for external fixator devices. Screw clamps are widely used in external fixators as a means to connect the half-pins to the fixator body....This work deals with the structural analysis of screw clamps for external fixator devices. Screw clamps are widely used in external fixators as a means to connect the half-pins to the fixator body. The analysis is carried out by both numerical and experimental techniques, based on the case study of a clamp produced by Citieffe (Bologna, Italy). As a preliminary activity, the tribological parameters involved in the screw-clamp interaction have been characterized by means of a mixed finite element analysis and experimental procedure. Then, an assessment of the current design of the clamp has been carried out. A re-design has been proposed, which, based on some targeted geometrical modifications, allows achieving higher strength requirements with the same overall dimensions and type of materials. A higher load-bearing capability for a given size may allow the fixator to be used on a broader population. Finally, a list of good practices for the design of this kind of clamps has been proposed.

A numerical and experimental approach to the design and failure analysis of a pinion shaft for wheel loaders

The present paper deals with the failure analysis and consequent design tips regarding a pinion shaft belonging to a differential gear for offroad machinery applications, namely wheel loaders. The motivations of the study arise from some in-field failures, which resulted in the fracture of the pinion shaft, originated at an external groove located at the end of its threaded portion. The issue has been tackled by means of analytical, numerical and experimental tools. The observed failures have been demonstrated to be due to the in-service loosening of a ring nut, whose function is to preload the tapered rolling bearings, which support the shaft. The weak points of the shaft design are highlighted and possible approaches to overcome the observed occurrence are presented at the end of the study.

DMLS Built Maraging Steel Fatigue Response Investigated for Different Build Orientations and Allowance for Machining

This work derives its motivations from the increasing interest towards Additive Manufacturing and the lack of studies, mainly in the field of fatigue. The effect of build orientation and of allowance for machining on DMLS produced Maraging Steel MS1 has been assessed. The experimental results, properly set up by tools of Design of Experiment, have been statistically processed and compared. The outcomes were that, probably due to effect of the thermal treatment, machining and material properties, the aforementioned factors do not have a significant impact on the fatigue response. This made it possible to work out a global curve, accounting for all the result. Fracture surfaces have been carefully studied as well.

Effects of Machining and Heat and Surface Treatments on as Built DMLS Processed Maraging Steel

The main motivations for this study arise from the need for an assessment of the fatigue performance of DMLS produced Maraging Steel MS1, when it is used in the “as fabricated” state. The literature indicates a lack of knowledge from this point of view, moreover the great potentials of the additive process may be more and more incremented, if an easier and cheaper procedure could be used after the building stage. The topic has been tackled experimentally, investigating the impact of heat treatment, machining and micro-shot-peening on the fatigue strength with respect to the “as built” state. The results indicate that heat treatment significantly enhances the fatigue response, probably due to the relaxation of the post-process tensile residual stresses. Machining can also be effective, but it must be followed (not preceded) by micro-shot-peening, to benefit from the compressive residual stress state generated by the latter.

The Front Suspension

In this chapter, the authors introduce the telehydraulic fork, which has become, across the years, the most common kind of front suspension for motorbikes. In chronological order, some noteworthy patents are presented, which help the reader following the main steps of the technical evolution which gave front motorbike suspensions their current shape. Then, the behaviour of some key structural elements of the fork is examined, under the assumption that the fork is subject to a bending moment acting on the front wheel mid-plane. Such a noteworthy loading condition is frequently encountered during the life cycle of a motorbike: consider, for instance, an emergency braking manoeuvre. Tests which simulate the effect of a hard braking on the fork are also part of the product validation programmes of the main motorbike producers. It is illustrated an analytical model useful for calculating the stress state of the fork legs under said loading condition. Such a model takes into account some architectural configurations as well as some characteristic geometrical parameters of the fork and of the motorbike. The model was validated referring to some production forks, both by finite element analyses and by experimental tests on the road. In the case of forks equipped with a single brake disc, the load unevenness between the legs during braking is analysed, and some strategies aimed at reducing such loading unbalance are suggested. The model presented herein could be helpful for designers who are developing new fork models, because it allows foreseeing critical issues due to legs dimensioning since the early phase of product development, when FEA techniques may be difficult to implement.