L. Solazzi

The effect of block braking on the residual stress state of a solid railway wheel

Abstract A finite element, numerical model of a solid railway wheel was perfected permitting the simulation of a block braking operation. The analyses performed, backed by experimental tests, permitted the degree of variation in the residual stress state (induced by differential quenching heat treatment and successive tempering) caused by particularly heavy braking to be evaluated. The results highlight the influence of the main braking parameters (force and time) and the thermal history previously suffered by the wheel. Finally, the thermal fatigue strength of the component, although in an approximate way, was checked on the basis of the calculated stress state and through the introduction of the data of a real and particularly significant route into the model. This demonstrated the broad safety margin with which the wheel operates and also brought to light the dangerous nature of particularly severe braking which can drastically modify the residual stresses induced by the heat treatment, moving them towards tensile stresses.

Effect of Different Corrosion Levels on the Mechanical Behavior and Failure of Threaded Elements

This research concerns the study of corrosion effects on different threaded elements to analyse bolted joints working in a saline environment. In particular, this article examines the mechanical behavior of a M8 junction realized by different steels and subjected to different degrees of corrosion. Four materials were investigated: a low-alloyed structural steel in the original condition and the same after zinc-plating; a quenched and tempered steel; and an austenitic stainless steel. For each steel were tested a certain number of threaded rods exposed to a saline water solution, simulating the atmospheric exposure to an aggressive environment. The samples were characterized by different intervals of exposure. During these periods, the threaded elements (threaded rods) were kept in tension applying a tightening torque proportional to the yield strength of the tested steel, to evaluate their susceptibility to stress corrosion cracking. Before and after the different corrosion steps, some metallographic analyses, static tensile and fatigue tests, were carried out to determine, for each sample, the degree of corrosion and its influence on the reduction of the junction resistance. In order to evaluate the stress-intensifying factor and its variation with the imposed degree of corrosion was carried out a FEM analysis.

Estimation Of The Dynamic Effect In The Lifting Operations Of A Boom Crane.

This paper describes a model for the study of the dynamic behavior of lifting equipments. The model here proposed allows to evaluate the fluctuations of the load arising from the elasticity of the rope and from the type of the motion command imposed by the winch. A calculation software was developed in order to determine the actual acceleration of the lifted mass and the dynamic overload inside the rope during the lifting phase. In the final part of the article an application example is presented, with the aim of showing the correlation between the magnitude of the stress and the type of the employed motion command.

Wheel rims for industrial vehicles: comparative experimental analyses

This work presents the results of a series of experimental analyses intended to define two different types of wheel rim for industrial vehicles. The main tests carried out were the following: testing on a rotating bending machine; testing on a rolling machine; in the field, namely a series of experiments on wheel rims placed on a hydraulic dump hoist that was subjected to defined loading conditions. These analyses revealed that the extent and nature of the stress on the wheel rims imposed by the three tests were not particularly correlated. The axial and radial rigidity of the rims meant that certain tests stressed one wheel rim more than another.

Effect of shot peening on carburised surfaces

The aim of this work is to examine the residual stress distribution in carburised steel components subjected to shot peening. A numerical model of the shot peening was developed by means of the ABAQUS explicit code, taking into account the variation in the material mechanical properties from the surface towards the core, defined on the base of the microhardness profile experimentally measured. The rate dependent hardening of the material was also considered for these analyses, together with the softening due to the heat generation during the impact. The model was verified by experimental residual stress measurements carried out on disk specimens, carburised and shot peened as in a typical industrial application. The analyses, repeated for different values of shot velocity and dimensions, show the influence of these parameters and that of the carburising depth on the final residual stress distribution.

New design concept of a downhill mountain bike frame made of a natural composite material

In this work, the design of a new downhill mountain bike frame, made with an innovative natural composite, is presented. The study is based on an early finite element analysis of the characteristics and performance of a standard frame made of aluminum, allowing to define the loading conditions and to provide a design optimization of the frame in different race situations. The model was later implemented with the properties of a natural reinforced composite. The results obtained show that the new composite allows a weight reduction with a stiffness and a safety coefficient comparable to the standard aluminum frame.

Influence of the Manufacturing Process on Defects in the Galvanized Coating of High Carbon Steel Wires

This study is a detailed failure analysis of galvanized high carbon steel wires, which developed coating cracks during the torsion test performed as a quality control at the end of the manufacturing process. Careful visual inspections showed that the cracks are already present in the coating before the torsion test. In order to explain the origin of these cracks, systematic metallographic investigations were performed by means of optical and scanning electron microscope on both the wires and the rods that have been cold drawn to produce the wire. The chemical composition of the galvanized coatings was evaluated by means of energy dispersive spectroscopy. Micro bidimensional X-ray diffraction experiments were also performed to measure the residual stresses in the galvanized coating. The results showed that the failure is related to two main factors: the relatively high content of silicon in the steel and the unsuitable cooling rate of the rods at the exit from the galvanizing bath. The mechanism proposed to explain the origin of the defects was supported by Finite Elements Methods simulations and verified with in-plant tests. The proper countermeasures were then applied and the problem successfully solved.

Failure Analysis of a Cyclic Contact Testing Machine Pin

The goal of this paper is to investigate the failure of a mandrel pin mounted on a rolling contact test bench. For this purpose, different methods of analysis were conducted, including metallography and stress analysis. The stress values in the failed pin were determined by Finite Elements. The high notch effect and the incorrect mounting of the specimens were identified as the failure causes. A pin design change is proposed to reduce the maximum stress even in the case of incorrect specimen mounting.

Experimental Investigation on the Crack Closure Phenomenon Using Barkhausen Noise Method

This paper presents an experimental investigation on a middle tension (MT) specimen made of a low carbon structural steel subjected to cyclic loading. The work was aimed to assess the effectiveness of Barkhausen Noise method in detecting the crack closure phenomenon. The Influence of probe orientation and position ahead the crack tip was examined, in order to optimize the magnetic measurements. A filtering procedure was also used to treat the Barkhausen Noise signal. A procedure was proposed to determine the crack-opening load from it. On the same specimen, some strain gauge measurements were carried out to determine the crack-opening load by the local compliance method. The results showed a good agreement of the results obtained with the two experimental techniques.

Dynamic and acoustic properties of a joisted floor

Lightweight structures find more and more applications in both vehicle and ship industries. To meet a growing demand, a variety of different types of joisted panels have been developed during the last few decades. One of the problems to deal with is the assessment of the acoustic performances of such panels once they are already mounted in their final place. In this case, it can be of importance to find a way to characterise their dynamic and acoustic properties, such as bending stiffness, internal losses and sound reduction index through non-destructive testing. A method for a quick determination of the bending stiffness of a lightweight joisted floor is presented. On the basis of the apparent bending stiffness and of the losses, it is possible to predict the sound reduction index of the panel in a fairly simple way. The results obtained from the mobility tests have been compared to the measurements carried out according to the ISO standard procedure.