Finite Element Analysis and Experiments for Predicting Fatigue and Rolling Contact Fatigue Behavior of Spur Gears

This paper presents the Finite Element (FE) analyses carried out with the aim to predict the tooth root fatigue and Rolling Contact Fatigue (RCF) behavior of spur gears, in terms of crack propagation maximum number of cycles. The combination of different materials, i.e. steel and titanium, and surface treatments, i.e. case-hardening and application of surface layers by Physical Vapor Deposition (PVD), are investigated. The residual stresses induced by the deposition of the coating are modelled. The stress intensity is described by linear elastic relations based on the crack tip opening displacement and the crack propagation in the case-hardened spur gears is described with the help of mathematical models. Experiments are carried out to evaluate tooth damage under RCF for different treated gears. The best solutions in terms of bulk material – treatment combination among the ones investigated are identified, also highlighting innovative possibilities which can guarantee appreciable performance

Numerical and theoretical models to predict fatigue life in aggressive environments from experimental data

Corrosion fatigue produce sensible effects in the fracture mechanics of structural materials. Aggressive environments in presence of dynamic fatigue load are indeed responsible of multiple effects, regarding crack nucleation and propagation rates. Considering Ti-6Al-4V in air, inert paraffin oil and 3.5 wt.% NaCl mixture, environmental effects are sensible in terms of acceleration of Fatigue Crack Growth Rate – i.e. da/dN vs. stress intensity factor ΔK. Several literature studies dealt with the topic in the past years. However, research has been focused mainly on the FCGR description, and the prediction of number of cycles to failure in aggressive environments is not addressed. In the presented poster, a methodology to obtain a numeric model which reconstruct da/dN vs ΔK from experimental results, including crack length and applied stress, is presented and compared against literature data. Results are related to R = 0.1 axial test involving smooth and notched flat dogbone specimens, with varying notch radius. The proposed model is used to reconstruct the number of cycles to failure of the tested specimens, resulting in a satisfactory correlation with experimental data. Comparison with other literature models highlights the necessity to develop a proper numerical model with each test case. Please click Additional Files below to see the full abstract

study on a new mobile anti terror barrier

Abstract The vehicle-ramming terror attacks in Berlin, Barcelona, London and Nice highlighted our vulnerability: all of us could be wounded or killed during a walk in a crowded place, it is sufficient a car, a van or a truck. The authors of this paper designed a planter full of water and mainly made of steel and cast iron. For this reason, this device serves as both mobile anti-terror barrier and street furniture. This barrier can stop a 3500 kg vehicle running at 64 km/h and the system itself in less than five meters as demonstrated by the experimental crash test. Starting from these considerations, a simplified mathematical model of the impact was developed and a finite element model was calibrated. The first one points out the main features needed by the obstacle; the second one is a good base for further analyses

A Numerical Method to Predict the RCF Behaviour of PVD-coated Transmission Gears and Experimental Results

This work studies the rolling contact fatigue (RCF) behaviour of case-hardened transmission gears for racing motorcycles both numerically and experimentally. Both as-produced and PVD-WC/C coated conditions are analyzed. Finite element models of the gears were developed and a calculation procedure was applied to predict their RCF life. The Ti-6Al-4 V alloy was also considered to investigate the mass decrease of the components. RCF tests were carried out in both dry and lubricated conditions. The experimental results were compared with the numerical ones to check the reliability of the predictive method proposed

Multifactorial Activation of NLRP3 Inflammasome: Relevance for a Precision Approach to Atherosclerotic Cardiovascular Risk and Disease

Chronic low-grade inflammation, through the specific activation of the NACHT leucine-rich repeat- and PYD-containing (NLRP)3 inflammasome-interleukin (IL)-1\u3b2 pathway, is an important contributor to the development of atherosclerotic cardiovascular disease (ASCVD), being triggered by intracellular cholesterol accumulation within cells. Within this pathological context, this complex pathway is activated by a number of factors, such as unhealthy nutrition, altered gut and oral microbiota, and elevated cholesterol itself. Moreover, evidence from autoinflammatory diseases, like psoriasis and others, which are also associated with higher cardiovascular disease (CVD) risk, suggests that variants of NLRP3 pathway-related genes (like NLRP3 itself, caspase recruitment domain-containing protein (CARD)8, caspase-1 and IL-1\u3b2) may carry gain-of-function mutations leading, in some individuals, to a constitutive pro-inflammatory pattern. Indeed, some reports have recently associated the presence of specific single nucleotide polymorphisms (SNPs) on such genes with greater ASCVD prevalence. Based on these observations, a potential effective strategy in this context may be the identification of carriers of these NLRP3-related SNPs, to generate a genomic score, potentially useful for a better CVD risk prediction, and, possibly, for personalized therapeutic approaches targeted to the NLRP3-IL-1\u3b2 pathway. View Full-Tex

A numerical model to assess the role of crack-tip hydrostatic stress and plastic deformation in Environmental Assisted Fatigue Cracking

To better understand the mechanics of environmentally assisted cracking, and particularly hydrogen embrittlement, a correct description of the hydrostatic stress field is indispensable. The concentration of hydrogen in the proximity of the crack tip is indeed dependent of the hydrostatic stress effect on the microstructural lattice of the material. The overall parameters of the hydrostatic stress, including peak value, its location, gradient and distribution size are fundamental to assess the effect on hydrogen distribution near the crack tip. H concentration show indeed an exponential dependence on hydrostatic stress, so that even a moderate increase in the applied stress is traduced in a dramatic rise of hydrogen concentration. In order to investigate the mechanism beneath hydrogen embrittlement, a proper modelling of the hydrostatic stress is mandatory. Moreover, strain hardening might significantly interfere with the actual stress distribution, thus becoming a relevant parameter. The stress and strain field is also deeply affected by the presence of sharp notches. In the present work, a detailed Finite Element model, based on actual fatigue testing of notched Ti-6Al-4V specimens is proposed, providing a deeply informative tool to assess the hydrostatic stress and the plastic strain in the proximity of the crack tip. The data from the model are compared to available results and experiences in literature. Please click Additional Files below to see the full abstract

Fatigue behavior of notched Ti-6Al-4V in air and corrosive environment

Abstract The broad use of titanium alloys in naval, automotive and aerospace applications expects the current research to shed light on the fatigue behavior of these materials in corrosive media and notched condition. In this respect, the fatigue behavior in air and NaCl solution of notched Ti-6Al-4 V flat dogbone samples was investigated. A step-loading method was used to generate data points on fatigue limit stress vs. Kt diagrams for a constant life of 200,000 load cycles at R = 0.1. Fracture surfaces were observed using stereoscopic microscope

Effects of environment and stress concentration factor on Ti-6Al-4V specimens subjected to quasi-static loading

Abstract The bimodal titanium alloy Ti-6Al-4V is a well-known high strength-to-mass ratio material in different engineering sectors. Furthermore, the rapid oxidation of the surface protects the base material from the interaction with a wide spectrum of corrosive environments. However, the presence of surface defects and the mechanical loading may compromise the effectiveness of the oxide film. Quasi-static loading tests were carried out on different smooth and notched Ti-6Al-4V specimens in order to analyze the role of environment and stress concentration factor

Targeting Immunity in End-Stage Renal Disease

Background: Despite the stable incidence of end-stage renal disease (ESRD), it continues to be associated with an unacceptably high cardiovascular risk. Summary: ESRD is characterized by enhanced oxidative stress and severe inflammation, which boost cardiovascular risk, thus increasing cardiovascular-associated mortality rate. While substantial effort has been made in the technological innovation of dialytic techniques, few significant advances have been made to reduce inflammation in patients with ESRD. Indeed, this contrasts with the extensive scientific breakthroughs made in the basic field of science in targeting inflammation. There is thus a pressing need for clinical trials to test the effect of reducing inflammation in patients with ESRD. Here, we will revisit the negative effect of ESRD on inflammation and explore the impact of enhanced inflammation on cardiovascular outcomes and survival in patients with ESRD. Finally, we will discuss the need for clinical trials that target inflammation in ESRD, as well as weigh potential disadvantages and offer novel innovative approaches. Key Message: We will try to understand why the issue of inflammation has not been successfully addressed thus far in patients with ESRD, while at the same time weighing the potential disadvantages and offering novel innovative approaches for targeting inflammation in patients with ESRD

Effects of FOD on fatigue strength of 7075-T6 hourglass specimens

The term "Foreign Object Damage (FOD)" refers to the damage associated with the impact of particles on aircraft engine components that causes changes in fatigue strength as a result of induced stress concentrations, residual stresses and microstructural changes. This paper presents the Finite Element (FE) models created to study the stress field induced by the impacts of a steel sphere on a 7075-T6 hourglass specimen. The impacts occur at the minimum cross section, in the normal and oblique directions. The results reveal that in the event of an oblique impact the axial tensile stresses are greater and closer to the crater created by the impact. The superposition of the residual axial stresses to the bending stresses by fatigue test allows to identify the areas in which the maximum stresses are reached and therefore crack initiation is expected