On the peak strength of 7050 aluminum alloy: mechanical and corrosion resistance

This 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

A simplified formula to estimate the load history due to ballistic impacts with bullet splash. Development and validation for finite element simulation of 9x21mm full metal jacket bullets

An original simplified formula is proposed to estimate the load history caused by ballistic impacts characterized by the so-called bullet splash phenomenon, consisting in the complete bullet fragmentation with no penetration of the target. The formula is based on the progressive momentum variation of the mass of the bullet impacting on a planar plate normal to the impact direction. The method aims at creating a simplified approach to assess the response of structures by means of explicit finite element simulations without the need of modelling the interaction between impactor and target. The results demonstrate that the proposed method can be used to estimate the forces generated by bullet-splash phenomena of 9x21mm full metal jacket bullets and effectively applied to finite element simulations allowing significant reductions in computational cost

FENOMENI DI FRETTING-FATIGUE SU UN CONDUTTORE ELETTRICO

I conduttori elettrici aerei per linee di alta tensione sono funi metalliche costituite da più fili avvolti ad elica in strati successivi attorno a un filo/anima centrale. La vita in servizio di questi componenti spesso è drasticamente ridotta dalle vibrazioni eoliche che generano, nella vicinanza dei morsetti di sospensione e dei dispositivi di ancoraggio, movimenti di scorrimento relativo di piccola ampiezza tra le superfici dei singoli fili a contatto tra loro. Questo fenomeno provoca sul componente il danneggiamento denominato fretting-fatigue, che rappresenta una delle cause principali di rottura dei fili dei conduttori e, in condizioni eccezionali, dell’intera fune. Scopo dell’attività di failure analysis qui descritta è identificare la morfologia nonchè comprendere la natura e le cause dei fenomeni coinvolti nel cedimento di un conduttore di tipo AAAC (in lega di alluminio 6101), composto da 61 fili (su quattro strati concentrici) appartenente ad una linea ad alta tensione a fascio binato senza ammortizzatori di vibrazione né distanziatori. Per lo svolgimento dell’attività è stata seguita una tipica procedura di failure analysis, prendendo in considerazione sia il conduttore danneggiatosi in esercizio che un conduttore nuovo delle medesime caratteristiche. L’analisi visiva e l’esame frattografico hanno evidenziato le tipiche caratteristiche morfologiche del fenomeno di fretting-fatigue; le prove di trazione e le analisi chimiche eseguite sia sul conduttore nuovo che su quello esercito hanno escluso la presenza di difetti o anomalie nel materiale. L’insieme degli esami effettuati ha permesso di identificare nei fenomeni di vibrazione eolica la causa scatenante del danneggiamento. Per evitare il ripetersi del fenomeno, si è consigliato l’attrezzamento della linea con distanziatori e ammortizzatori: tali accorgimenti hanno risolto in modo definitivo il problema lamentato

FENOMENI DI FRETTING-FATIGUE SU UN CONDUTTORE ELETTRICO

I conduttori elettrici aerei per linee di alta tensione sono funi metalliche costituite da più fili avvolti ad elica in strati successivi attorno a un filo/anima centrale. La vita in servizio di questi componenti spesso è drasticamente ridotta dalle vibrazioni eoliche che generano, nella vicinanza dei morsetti di sospensione e dei dispositivi di ancoraggio, movimenti di scorrimento relativo di piccola ampiezza tra le superfici dei singoli fili a contatto tra loro. Questo fenomeno provoca sul componente il danneggiamento denominato fretting-fatigue, che rappresenta una delle cause principali di rottura dei fili dei conduttori e, in condizioni eccezionali, dell’intera fune. Scopo dell’attività di failure analysis qui descritta è identificare la morfologia nonchè comprendere la natura e le cause dei fenomeni coinvolti nel cedimento di un conduttore di tipo AAAC (in lega di alluminio 6101), composto da 61 fili (su quattro strati concentrici) appartenente ad una linea ad alta tensione a fascio binato senza ammortizzatori di vibrazione né distanziatori. Per lo svolgimento dell’attività è stata seguita una tipica procedura di failure analysis, prendendo in considerazione sia il conduttore danneggiatosi in esercizio che un conduttore nuovo delle medesime caratteristiche. L’analisi visiva e l’esame frattografico hanno evidenziato le tipiche caratteristiche morfologiche del fenomeno di fretting-fatigue; le prove di trazione e le analisi chimiche eseguite sia sul conduttore nuovo che su quello esercito hanno escluso la presenza di difetti o anomalie nel materiale. L’insieme degli esami effettuati ha permesso di identificare nei fenomeni di vibrazione eolica la causa scatenante del danneggiamento. Per evitare il ripetersi del fenomeno, si è consigliato l’attrezzamento della linea con distanziatori e ammortizzatori: tali accorgimenti hanno risolto in modo definitivo il problema lamentato

Living Lab Experience in Turin: Lifestyles and Exposure to Black Carbon

State-of-the-art, continuous personal monitoring is a reference point for assessing exposure to air pollution. European air-quality standards for particulate matter (PM) use mass concentration of PM (PM with aerodynamic diameters ≤ 10 µm (PM10) or ≤2.5 µm (PM2.5)) as the metric. It would be desirable to determine whether black carbon (BC) can be used as a better, newer indicator than PM10 and PM2.5. This article discusses the preliminary results of one of the three living laboratories developed in the project “Combination of traditional air quality indicators with an additional traffic proxy: Black Carbon (BC)”. The Living Lab#1 (LL#1) involved 15 users in the city of Turin, Italy. Three portable aethalometers (AE51) were used to detect personal equivalent black carbon (eBC) concentrations in the respiratory area of volunteers at 10-s intervals as they went about their normal daily activities. The Geo-Tracker App and a longitudinal temporal activity diary were used to track users’ movements. The sampling campaign was performed in November for one week. and each user was investigated for 24 h. A total of 8640 eBC measurements were obtained with an average daily personal exposure of 3.1 µg/m3 (±SD 1.3). The change in movement patterns and the variability of microenvironments were decisive determinants of exposure. Preliminary results highlight the potential utility of Living Labs to promote innovative approaches to design an urban-scale air-quality management plan which also includes BC as a new indicator

A Simplified ALE model for finite element simulation of ballistic impacts with bullet splash – development and experimental validation

An original simplified finite element model is proposed to simulate the effects of non-penetrating ballistic impacts causing the so-called bullet splash phenomenon (complete bullet fragmentation), while no fragmentation is caused to the target. The model is based on the Arbitrary Lagrangian Eulerian formulation (ALE) and it simulates the impact as a fluid-structure interaction. The bullet splash phenomenon has been tested by experimental analyses of AISI 304L plates impacted by 9x21 FMJ (full metal jacket) bullets. The model has been developed with the aim of creating a simplified approach to be used in the industry and forensic sciences to simulate the non-penetrating interaction of soft impactors with hard targets. Comparisons between evidence and simulation results lead to the conclusion that the proposed approach can be used in a conservative way to estimate both local and global effects of bullet-splash phenomena

A simplified constitutive model for a SEBS gel muscle simulant - Development and experimental validation for finite elements simulations of handgun and rifle ballistic impacts

An original simplified constitutive model is proposed to simulate the effects of ballistic impacts on blocks of synthetic muscle simulant based on mineral oil and styrene ethylene-butylene styrene polymers (SEBS) as a convenient substitute for Fackler ballistic gelatin. The model is based on a quasi-static elastic-plastic model associated with hydrodynamic properties regulated by a polynomial equation of state. The paper illustrates the development and experimental validation of the model to simulate 9x21mm FMJ round-nose, 7.62x39 mm FMJ, and 5.56x45 mm NATO bullets penetrating 145x145x400 mm gel blocks. All material parameters are provided to be implemented in built-in LS-Dyna keywords. The validation confirms the effectiveness of the model and suggests possible further developments. The work also confirms the tested synthetic gel as a valid and convenient substitute for Fackler 10% ballistic gelatin at 4 °C

Failure analysis of boron steel components for automotive applications

The automotive industry is continuously looking for an innovative mix of new steels and manufacturing techniques in order to improve process chain efficiency and cost reduction. To this aim, boron steels are becoming increasingly popular thanks to their high hardenability and machinability. Due to their reduced finishing steps, boron steels are commonly processed using fine blanking technologies. The success of fine blanking on boron steel components is due to heat treatments which must be carefully designed to avoid precipitation of boron-rich compounds that would lower steel hardenability. At high temperature, boron is very reactive with oxygen and nitrogen. The main focus of this paper is to show some drawbacks that can occur during heat treatments of automotive components. An experimental campaign was performed on two different boron steels, namely EN 34MnB5 and EN 22MnB5. The steel samples were previously spheroidized annealed in a neutral environment (hydrogen/nitrogen atmosphere), and then fine blanked to obtain specific automotive components which were subsequently quenched and tempered. Experimental tests revealed precipitation of nanometric compounds, causing strong grain refinement and localized decrease of steel hardenability. Hardenability problems were brought back to nitrogen pick-up during initial spheroidize annealing treatments