1,721,017 research outputs found
La ricostruzione dello scenario di incendio parte dall'analisi dei reperti in metallo
No full textLe potenzialità dell’analisi metallurgica e metallografica
dei reperti provenienti dalle zone coinvolte in un incendio.
Dalle simulazioni d’incendio su componenti, realizzati in lega d’alluminio, in rame o lega di rame, sono stati ottenuti dei campioni, poi esaminati in laboratorio tramite microscopia ottica e microscopia elettronica a scansione
(SEM) con microsonda a dispersione d’energia (EDS)
Dai reperti in metallo la radiografia dell'incendio
No full textL'analisi metallurgica di questi materiali rappresenta un utile metodo di indagine per individuare le temperature sviluppate durante un incident
Influence of Heat of Non-Ferrous Objects: Metallurgical Analysis in Fire Science Investigations
No full textNFPA 921 is a widely accepted standard to perform fire and arson analysis: it states that heat damage on items and components must be recognized to perform a more careful analysis of fire spread and to better define area and point of origin. With reference to metallic materials involved in a fire scene, NFPA 921 only indicate two useful parameters for temperature estimation, i.e. melting temperature and surface oxidation. However, the melting point of metals and alloys may define a wide range of temperatures (for example iron-based alloys normally melt between 1500 and 1600°C); in addition surface oxidation colors can only inform in a qualitative way. To better estimate the temperature range experienced by various items, much more information can be inferred from in-depth metallurgical analyses. Intergranular oxidation, recrystallization, second phase precipitations and incipient melting were some of the metallurgical features easily observable: if the investigator knows the approximate temperature of these microstructure modifications, a better estimate can be done of the “effective fire temperature” that the material might have reached. To this aim some components that can be found in fire a scene (aluminium airshaft, brass tap and copper gas pipe) were exposed to simulated fire conditions of known time durations and peak temperatures. The collected items were then examined by metallurgical techniques, identifying reference temperatures. The obtained results can give useful information to understand the fire scene
Gli acciai per cuscinetti a rotolamento
No full textLa corretta scelta di un cuscinetto a rotolamento è un aspetto di vitale importanza, considerato
il ruolo fondamentale da esso svolto all’interno delle macchine o dei sistemi meccanici.
Conseguentemente, sia l’acciaio utilizzato sia le tecnologie di produzione impiegate devono essere
valutate con attenzione per ottenere livelli di qualità ripetibili e caratteristiche sempre più performanti
In-depth approach to fire investigations: microstructural analysis of metallic materials
Full text linkFailure analysis normally requires many forms of investigation, but visual examination is the most used amongst all possible techniques. However, as the legal climate for fire investigation is becoming more rigorous, fire researchers need to work differently. In other words, to be technically defensible, expert testimony must be built on scientific data. To this aim, in-depth microstructural analyses of materials are particularly suitable to define the fire scene. This paper discusses some of the basic metallurgical theories used in failure analysis of copper, steel and aluminium alloy components involved in fire situations. Some components that can be easily found in fire and arson scene were submitted to simulated fire for indicated time and temperature. The collected samples were than examined by optical microscopy, scanning electron microscopy and energy-dispersive spectroscopy. Oxidation, recrystallization, second-phase precipitation and melting were some of the features observed on samples that can be strictly related to the thermal effect of fire. On the basis of these metallurgical results and starting from the evidence that different exposure temperatures can induce different metallurgical modifications, it is possible to define the temperature range experienced by various components, thus suggesting the fire dynamic during the incident
Fenomeni di danneggiamento dei materiali metallici dovuti all’esercizio (Failure Analysis)
No full text
On the peak strength of 7050 aluminum alloy: mechanical and corrosion resistance
Full text linkThis work consists of an experimental study on the ageing response and resulting properties of AA7050 plate material. New heat treatments are investigated for achieving a peak-aged temper, as a T6 temper may be said to be, that achieves yield and tensile strengths superior to those of the documented T7 treatments. For this alloy, the Standard establishes T7X tempers which were developed to obtain a very good compromise between mechanical strength and corrosion resistance. Nevertheless, for all those applications in which the environment is not considered critical for corrosion behaviour, the peak strength condition could be beneficial. In this experimental work, the authors use standard hardness testing to investigate mechanical response as a function of ageing time at several ageing temperatures, all applied immediately after solution. Upon identifying specific times and temperatures of interest, specimens aged under the selected treatments were subjected to tensile testing and intergranular corrosion testing. The results show that a single-step ageing heat treatment is able to produce a significantly high both yield and ultimate tensile strength. Moreover, the corrosion test data indicates that this new heat treatment produces corrosion resistance similar to that of the T76 heat treatment
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