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In many applications such as machining, metal forming, high-velocity impact, or high energy deposition on metals, materials are deformed at very high rates and in many cases also at high temperature. The stress–strain response of materials and structures will be a balance between the effects of hardening (due to strain and strain-rate) and thermal softening: temperature and strain-rate sensitivities are mutually related, and the thermal effects obtained from quasistatic tests cannot always be used to predict material response under dynamic loading conditions. Hence, the need to investigate the mechanical response of materials in a properly defined range of interest: the development of testing methodologies and facilities able to completely explore it is the starting point. The chapter collects and analyzes some experimental techniques applicable for impact and high strain-rate tests at high temperatures focusing the attention on methodologies and related problems and providing a review of the solutions adopted by researchers in the last decades.

Nickel-based superalloys have several applications for components exposed to high temperatures and high strain rate loading conditions during services. The objective of this study was to investigate the tensile properties of Inconel 718 produced using the laser metal deposition technique. Specimens with different heat treatments were investigated. Experimental tests were performed at the DYNLab at Politecnico di Torino (Italy). The temperature sensitivity was investigated between 20 °C and 1000 °C on a Hopkinson bar setup at a nominal strain rate of 1500 s−1. The specimens heating was obtained by means of an induction heating system, and the temperature control was performed by thermocouples, an infrared pyrometer, and a high-speed infrared camera. The thermal images were analyzed to check the uniformity of the heating and to investigate the presence of adiabatic self-heating. The results showed that the materials strength exhibited a significant drop starting from 800 °C. The strain rate influence was investigated at room temperature, and limited sensitivity was found covering six orders of magnitude in the strain rate. A preliminary analysis of the fracture mode was performed. Finally, different solutions for the strength material modeling were proposed and discussed with the aim of identifying models to be used in finite element simulations.

Three-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur.

Nickel-based superalloys show high strength retained also at high temperature and they are widespread used for structural components exposed during services to high temperature combined with high strain rate or impact loading conditions. The objective of this study was the investigation of the plastic flow behaviour of Laser Metal Deposited Nickel-based superalloy Inconel718. The material was manufactured at Northwestern Polytechnical University in China. Specimens with three different heat treatment conditions were investigated: as-deposited, directly aged and aged after homogenization and solution. High strain rate tensile tests were performed on the direct Hopkinson bar setup developed at DYNLab laboratory at Politecnico di Torino. At a nominal strain rate of 1500 s-1the temperature sensitivity was investigated between 20 and 1000°C. An induction heating system was adopted, and the temperature was monitored by thermocouples and infrared pyrometer and high-speed camera. The results showed the materials strength decreases as a function of temperature with a significant drop starting from 800 °C. An asymmetric tension-compression behaviour was found by comparing the results with data in compression. The strain rate influence was investigated at room temperature and very limited or negligible sensitivity was found covering six orders of magnitude in strain rate.

The objective of this work is the tune of a methodology for the determination of the fracture toughness in ductile materials at high strain-rate by means of dynamic 3 Point Bending (3PB) tests. The specimens made in high strength steel have been pre-cracked in fatigue with a single edge notch. The dynamic loading conditions have been reached by means of a modified Split Hopkinson pressure Bar setup, in which two small diameter bars are used as transmitted bars instead of the standard single one. In order to obtain the maximum amount of information from each test, different measuring systems have been adopted, in addition to the strain measurements on the bars performed using semiconductor strain-gages. On the specimen surface, one or two crack-gages (one for each side for specimens) have been bonded for obtaining data about the crack propagation and the crack tip position vs. time curve. Moreover, a high speed camera has been used for obtaining the measurements of the Crack Opening Displacement (COD) and the opening velocity: digital images have been processed using tracking techniques following some points on the specimen notch and input bar tip. Starting from the experimental measurements in term of force, displacement and crack-gage data, a protocol for fracture toughness calculation at the initiation stage of the crack growth in dynamic condition has been defined and a hybrid experimental – numerical methodology has been used. One of the key variables for the determination of dynamic initiation fracture toughness is the crack time to initiation. Many efforts have been done in order to better determine a precise method to experimentally measure this entity: this datum has been obtained from the analysis of both the force and crack-gage vs. time signals and the COD measurement on high speed video. Good agreement has been found between the two methodologies. At this stage, a 3D model, which simulates the SE(B) specimens during the Hopkinson 3PB test, has been done in order to determine the toughness (J integral) as a function of time. Knowing the initiation time, the fracture toughness at crack initiation can directly be determined.

This paper presents the results obtained from the investigation of the mechanical behaviour of two different batches of pure tungsten specimens. The interest in pure tungsten is due to its special properties, which has led to it finding applications in several fields, including nuclear physics. At this moment, it is used as a core material for fixed particle producing targets in several accelerator facilities around the world and it is a candidate for future ones. In these facilities, tungsten directly interacts with high energy proton beams and, consequently, is subjected to considerable deformation at high strain-rates and temperatures. From these considerations, there comes the need to properly investigate the material response under these extreme conditions. For this purpose, an ad-hoc testing campaign was performed on small dog-bone specimens in tension. The results will be applicable to the ongoing design of CERN’s AD-target as well as to other future tungsten targets operating at high power and dynamically loaded in multiple accelerator facilities. Due to tungsten’s high Ductile-to-Brittle Transition temperature, it was not possible to test it at temperatures less than 250 °C. Tests were performed at two different strain-rates (nominal value of 1 s−1 and 103 s−1) reaching a maximum temperature of 1000 °C. The dynamic tests were performed by using a Hopkinson Bar setup in the direct impact configuration. Both at low and high strain-rates, heating of the specimen was achieved using an induction coil system. A numerical inverse procedure was applied to analyse the experimental data with the aim to obtain the equivalent stress versus effective plastic strain at the different loading conditions to be used for calibration of the strength model and for the evaluation of strain-rate and thermal softening sensitivities of the material.

The niobium is currently used for the construction of the superconducting radio frequency (RF) Crab Cavity for the particle accelerator LHC at CERN in Geneva. An alternative technique to traditional forming methods is the electrohydraulic forming (EHF), in which ultrahigh-speed deformation of blank sheets is performed by using shockwaves electrically induced in water. A big effort is made for the analysis of the forming processes by FEM simulations, which require the definition of an appropriate flow stress material model. With this aim, in the present work, a testing campaign was performed in tension on sheet specimens with a rectangular cross-section at different strain-rates, up to 103 s-1. The obtained results showed the material is strongly sensitive to strain-rate, as expected for a pure BCC metal. The data, were processed via a reverse engineering procedure, based on finite element simulations of the experimental tests. This methodology allowed the identification of a tabular flow stress model (MAT_224 implemented in LSDYNA) for the prediction of the material behaviour as a function of the plastic strain, strain-rate and temperature.

The simulation of impact scenario against a structure requires the use of material models able to reproduce all aspects of the mechanical behaviour of the involved materials; plastic flow is one of the main aspects to be reproduced. In more detail, attention has to be paid to the investigation of strain-rate and temperature sensitivities, as well as their interaction, which necessitates the use of a reverse engineering approach. The present paper mainly focuses on the tensile behaviour and an ad-hoc testing campaign was performed on cylindrical dog-bone specimens made in Al6061T6 at different temperatures and strain-rates extending the range up to a level where, at present, there is a lack in the scientific literature. The thermal softening effect was investigated in quasi-static as well as in dynamic loading conditions from room temperature up to 400 °C; while the material strength dependence on the strain-rate was studied up to 104 s−1 on miniaturized samples. Microstructure analyses were performed to better investigate the mechanical response at different loading conditions. The parameters of the Johnson-Cook model were identified starting from experimental data via a numerical inverse approach based on FEM simulations. These parameters can be used for simulations of extreme loading scenario like ballistic impact events.

The reliability of the numerical results strongly depends upon the choice of the constitutive models, which sometimes requires an ad-hoc calibration of the parameters starting from experimental results. Often, the tension test is chosen since it allows obtaining a big amount of data, but in case of ductile materials, in which the specimen could be subjected to high value of plastic strain before the fracture, it is necessary to properly manage the experimental results. For low values of deformation, the deformation of the gage length of the specimen is uniform and the true stress can be easily derived from the longitudinal one and considered as the equivalent stress. At the onset of necking, geometrical instability and concentration of deformation are developed. In the scientific literature several different approaches have been proposed in order to estimate the equivalent stress distribution in the post-necking regime. In this work, a new approach was proposed by the combination of digital image analysis and numerical inverse method. The evolution of the profile deformation of the specimen observed during the test is directly used to identify the constitutive relation of the material in case of dynamic tensile tests.

Intense and high energy proton beams are impacted with fixed materials (targets) in order to produce new particles and secondary beams at CERN. In some of these targets, the requirement of reaching high yield production of secondary particles points out to the use of high density materials. The interaction of the beam with the atoms and nuclei of these materials produce extremely fast depositions of energy, highly soliciting them from thermo-structural point of view due to subsequent rise of temperature and pressure waves. Iridium is a good candidate material since exhibits very high density, high melting point, good strength and stability at high temperature, and resistance to thermal shock. The main goal of this study is the investigation of the mechanical behaviour at different temperatures and strain-rates in tensile loading condition of pure iridium. A series of tests at room temperature at different strain-rates (from 10−3 s−1 up to 104 s−1) was performed in order to obtain information about strain and strain-rate sensitivity of the material. In addition, a series of tests at different temperatures in both quasi-static and high strain-rate loading conditions was performed in order to obtain information about the thermal softening of the material (from room temperature up to 1250 °C). The experimental data were used to identify a strength model able to predict the material behaviour over wide ranges of variation of the variables of interest.

The aim of this work is to identify the tensile strength of alumina (Corbit98), by performing Brazilian tests at different loading rate. In this kind of test, generally used for brittle material in static loading conditions, a cylindrical specimen is diametrically compressed and failure is generated in the middle of the component as a consequence of a positive tensile stress. In this work, this experimental technique was applied also in dynamic loading conditions by using a setup based on the Split Hopkinson Pressure Bar. Due to the properties of the investigated material, among which are high hardness, high compressive strength, and brittle behaviour, some precautions were needed to assure the validity of the tests. Digital Image Correlation techniques were applied for the analysis of high framerate videos.

The prediction of material response in case of interaction with successive high energy proton bunches requires new tools and multidisciplinary approaches. The impact leads the propagation of shock-waves, which travels through the hit component causing a substantial density reduction and the appearance of tunneling effect along the beam direction. For taking into account this effect, an automatic procedure, consisting in coupling FLUKA Monte-Carlo and FE LS-DYNA codes, is developed. The case study consists of the accidental loss of 60 bunches of one of the 7TeV proton beams of the Large Hadron Collider (CERN) on a tungsten collimator.

High chromium ferritic/martensitic steel T91 (9% Cr, 1% Mo), on account of its radiation resistance, is a candidate material for nuclear reactor applications. Its joining by an impact method to create a cold joint is tested in the realm of scoping tests toward the safe operation of nuclear fuels, encapsulated in representative T91 materials. Hitherto, T91 mechanical characterization at high strain rates is relatively unknown, particularly, in relation to impact joining and also to nuclear accidents. In this study, the mechanical characterization of T91 steel was performed in tension by varying the strain-rate (10−3 up to 104 s−1) and temperature (20-800°C) on dog-bone specimens, using standard testing machines or Hopkinson Bar apparati. As expected, the material is both temperature and strain-rate sensitive and different sets of parameters for the Johnson-Cook strength model were extracted via a numerical inverse procedure, in order to obtain the most suitable set to be used in this field of applications.

Strain rate and temperature are variables of fundamental importance for the definition of the mechanical behavior of materials. In some elastic-plastic models, the effects, coming from these two quantities, are considered to act independently. This approach should, in some cases, allow to greatly simplify the experimental phase correlated to the parameter identification of the material model. Nevertheless, in several applications, the material is subjected to dynamic load at very high temperature, as, for example, in case of machining operation or high energy deposition on metals. In these cases, to consider the effect of strain rate and temperature decoupled could not be acceptable. In this perspective, in this work, a methodology for testing materials varying both strain rate and temperature was described and applied for the mechanical characterization of Glidcop Al-15, a copper-based composite reinforced with alumina dispersion, often used in nuclear applications. The tests at high strain rate were performed using the Hopkinson Bar setup for the direct tensile tests. The heating of the specimen was performed using an induction coil system and the temperature was controlled on the basis of signals from thermocouples directly welded on the specimen surface. Varying the strain rate, Glidcop Al-15 shows a moderate strain-rate sensitivity at room temperature, while it considerably increases at high temperature: material thermal softening and strain-rate hardening are strongly coupled. The experimental data were fitted using a modified formulation of the Zerilli-Armstrong model able to reproduce this kind of behavior with a good level of accuracy.

The strain-rate sensitivity of brittle materials, such as glass, ceramics or concrete-like materials, is usually easier to be performed in compression. However, also the tensile behavior, which affects phenomena such as spalling, scabbing and fragmentation, has to be investigated to achieve an exhaustive characterization. In last decades, a lot of researchers suggested spalling test as one of the best ways to characterize dynamically brittle materials. This type of test is based on propagation and reflection of elastic waves: the fracture for spalling occurs when, in the material, the tensile stress state, obtained by the reflection on a free surface of a compressive pulse, exceeds the strength limit. These conditions are usually reached using a SHPB setup: a striker bar is launched against the input bar, which is in contact with a long bar specimen free at the opposite surface. In this work, the spalling test has been performed to investigate the dynamic tensile behavior of graphite. The apparatus is actuated by a pneumatic gas-gun (1.5 m long). Striker and input bars are made of high-strength steel 10 mm of diameter. Different striker lengths are used (100 and 80 mm) to obtain different pulse lengths and amplitudes. The input bar is 3.4 m long and is instrumented in the middle. The specimens are 200 mm long and 10 mm of diameter, instrumented at 80 from the free surface with strain-gages.

This work shows the results obtained from the investigation of the mechanical behavior of two batches of pure molybdenum specimens (≥99.97 % Mo, Mo1 supplied by Plansee and Mo2 supplied by AT&M) under static and dynamic loading conditions at different temperatures, both under tensile and compressive loading conditions. Due to its properties molybdenum has applications in several fields including nuclear. At this moment, it is a good candidate for structural material application for Beam Intercepting Devices of the Large Hadron Collider at CERN, Geneva. The experimental tests in tensile loading condition were performed on small dog-bone specimens. A series of tests at room temperature and a range of strain-rates was performed in order to obtain information about the strain-rate sensitivity of the material. A series of tests at different temperatures in both static and high dynamic loading conditions was performed in order to obtain information about the thermal softening of the material. The dynamic tests were performed using the Hopkinson Bar technique, and the heating of the specimen was performed using an induction coil system. The experimental tests in compression were carried out on cylindrical specimens at room temperature and a range of strain-rates. The experimental data were analyzed via a numerical inverse method based on Finite Element numerical simulations. This approach allows to obtain the effective stress versus strain curves, which cannot be derived by using standard relations since instability and necking were present. Moreover, it also allows the non-uniform distribution of strain-rate and temperature inside the specimen to be accounted for. The results obtained from compression tests confirm the data obtained in tension in terms of strain-hardening and strain-rate sensitivity, even if the material exhibits a tension–compression asymmetry of the behavior. The analysis of the hardening, temperature and strain-rate sensitivities reveals that a unique standard visco-plastic model could not be defined to reproduce the material strength behavior under different loading conditions, especially over wide range of variation of the variables of interest.

In this work, the mechanical behavior of syntactic foams made of hollow glass microspheres mixed in an iron matrix was investigated. This type of material is interesting since, when compared to other types of metal foams, it offers greatly increased quasi-static compressive strength, though at lower maximum porosity and thus higher density. Moreover it maintains the advantages and useful properties of metal foams such as thermal and environmental resistance. In particular, the strain-rate sensitivity response was studied. The experimental characterization was performed by means of compression tests at three strain-rate levels: at the highest strain-rate level a SHPB was used. Type and content of glass microspheres were also studied. The experimental results showed that the compression behavior of syntactic foams, similarly to the other types of foams, is strongly affected by all the examined factors. For what concerns the strain-rate, it was found to increase material characteristics in almost all cases. The influence of the matrix behavior on the composite was identified as the determining parameter in this respect. In order to evaluate the results obtained with the described tests campaign, the experimental data were further elaborated by means of an empirical analytical strain-rate sensitive model. The dependency of the material response on model parameters was widely discussed.

This study is performed in order to estimate the damage on copper components due to the impact of a 7 TeV proton beam in the Large Hadron Collider. The case study represents an accidental case consequent to an abnormal release of the beam, in which eight bunches impact directly the copper. The energy delivered on the components is calculated by the FLUKA Team at CERN using their Monte-Carlo code for calculation of particle transport and interactions with matter. The energy maps are used by the authors as input for the structural simulations carried out via the FEM code LS-DYNA. The evolution of the phenomenon is quite similar to what might happen during an explosion. The impacted part of the component reaches extremely high values of pressure and temperature and undergoes changes of state. The sudden increase in pressure originates outgoing shockwaves that, travelling through the component, lead to a substantial density reduction in the impacted part. The energy delivered on the component is sufficient to severely damage the target.

Pure tungsten or its alloys (WHA) find applications in several fields, especially due to the fact that these materials show a good combination of mechanical and thermal properties and they are commonly used in aerospace, automotive, metal working processes, military and nuclear technologies. Looking at the scientific literature, a lack in the mechanical characterization over wide ranges in temperature and strain-rates was found, especially for W–Ni–Cu alloys. In this work, the mechanical characterization and the consequent material modeling of the tungsten alloy INERMET® IT180 were performed. The material is actually used in the collimation system of the Large Hadron Collider at CERN and several studies are currently under development in order to be able to numerically predict the material damage in case of energy beam impact, but to do this, a confident strength model has to be obtained. This is the basis of this work, in which a test campaign in compression and tension at different strain-rates and temperatures was carried out. The dynamic tests were performed using Hopkinson Bar setups, and the heating of the specimen was reached using an induction coil system. The experimental data were, finally, used to extract the coefficient of three different material models via an analytical approach.

The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing either 40/60 vol.% of hollow glass microspheres (S60HS) or 40 vol.% of Fillite cenospheres was investigated. In these materials, the hollow particle shells as third phase besides matrix and voids can provide a strengthening effect with the potential of raising mechanical performance above that of conventional, two phase steel foams. Samples were produced by means of metal powder injection moulding (MIM) and subjected to characterization under compressive load, with special attention dedicated to strain-rate sensitivity. Four strain-rate levels were investigated, covering 6 orders of magnitude from 10−3 to 103 s−1. For the highest, a Hopkinson Bar apparatus was used. The influence of density on strength was determined for samples containing glass microspheres and described by a power law relationship. The foams mechanical strength was found to increase with strain-rate in accordance with the behaviour observed for the reference material without hollow particles. The data were compared with those obtained in a previous work, in which Fe99.7 matrix syntactic foams containing similar levels of glass microspheres were investigated. The higher strength of the AISI 316L materials is associated with differences in matrix properties. Differences in strain-rate dependence of mechanical properties between both materials can be explained qualitatively based on the fcc (AISI 316L) and bcc (Fe99.7) lattice structure. The introduction of Fillite cenospheres induced a further increase of specific strength. Under quasi-static conditions, samples of this type were found to reach the same yield strength as the reference material despite the reduction in density. The significantly lower strength of glass microsphere based AISI 316L foams can be related to the observed microstructures: due to the high processing temperature (1200 °C), glass microspheres are destroyed during sintering, their remainders forming glass inclusions, whereas thermally more stable cenospheres remain intact and can thus stabilize the pores. Finally, an empirical strain-rate sensitive model was adopted to reproduce the experimental data: the fitting procedure used to obtain the model parameters is explained and the influence of the strain-rate discussed. The model allows property prediction for additive content and strain-rate levels further to those evaluated experimentally.

In this work a complete study about the dynamic response of pure copper at high temperature is performed in tension, on dog bone specimens with cylindrical cross-section. The tensile tests varying the strain rate are performed from quasi-static to dynamic regime, covering six orders of magnitude. The heating of the specimens in quasi-static condition is obtained with an induction coil system, designed to concentrate the heat flux in the gage length of the specimen. The temperature range varies between 20 and 400°C. In the perspective to perform also tests in mixed loading conditions, in this work, a methodology for testing materials at high temperature and high strain rate is described. The method uses the standard Hopkinson Bar apparatus for direct tensile tests with the same heating system used in quasi-static tests. The obtained experimental results are analysed and finally compared with those available in the scientific literature.

Syntactic foams are produced by adding hollow particles to a solid matrix material. So far, few processes exist that allow manufacturing of such materials using steel matrices. Extremely versatile in this respect are powder metallurgical processes like metal powder injection moulding (MIM), which facilitate usage of different matrix alloys in combination with micro scale fillers. Existing studies on such materials mostly concentrate on quasi-static properties, with Fe99.7 matrices combined with glass microspheres as one exception for which dynamic data has been published. The present work extends the range of matrix materials by summarizing experimental studies on 316L stainless steel foams using glass microspheres as well as cenospheres for the role of introducing porosity. Quasi-static tensile and compressive properties have been evaluated at different density levels – namely 5 and 10 wt.-% of microsphere addition - and are contrasted to dynamic performance as determined by means of impact testing and Split Hopkinson Pressure Bar (SHPB) techniques. Failure mechanisms of the materials are discussed in view of the experimental results, evaluations of the foams’ structural characteristics and comparison with the aforementioned existing quasi-static and dynamic data on Fe99.7 syntactic foams. Furthermore, performance is qualitatively and quantitatively compared to other types of 316L stainless steel matrix foams, such as the so-called composite metal foams (CMF) investigated by Rabiei and Vendra (2009).

The present study investigates the high strain rate behavior of mesoporous metal matrix syntactic foams focusing on the dependence of compressive and tensile properties on strain rate. The strain rate range, covered both in compression and tension, extends from quasi-static conditions or 10−3 s−1 to 103 s−1. Syntactic foams based on commercial high strength hollow glass microspheres and Invar (FeNi36) matrix are produced by means of feedstock extrusion and subsequent sintering. Levels of glass microsphere addition examined are 5 and 10 wt%, respectively, corresponding to approximately 40 and 60 vol% of microspheres in the initial mix prior to sintering, and considering the metal and filler fraction only. Reference samples containing no microsphere addition have been included in the study. Mechanical testing is accompanied by metallographic examinations.

Predicting the consequences of highly energetic particle beams impacting protection devices as collimators or high power target stations is a fundamental issue in the design of state-of-the-art facilities for high-energy particle physics. These complex dynamic phenomena can be successfully simulated resorting to highly non-linear numerical tools (Hydrocodes). In order to produce accurate results, however, these codes require reliable material constitutive models that, at the extreme conditions induced by a destructive beam impact, are scarce and often inaccurate. In order to derive or validate such models a comprehensive, first-of-its-kind experiment has been recently carried out at CERN HiRadMat facility: performed tests entailed the controlled impact of intense and energetic proton pulses on a number of specimens made of six different materials. Experimental data were acquired relying on embedded instrumentation (strain gauges, temperature probes and vacuum sensors) and on remote-acquisition devices (laser Doppler vibrometer and high-speed camera). The method presented in this paper, combining experimental measurements with numerical simulations, may find applications to assess materials under very high strain rates and temperatures in domains well beyond particle physics (severe accidents in fusion and fission nuclear facilities, space debris impacts, fast and intense loadings on materials and structures etc.). (c) 2013 Elsevier B.V. All rights reserved.

Beam Intercepting Devices (BID) are designed to operate in a harsh radioactive environment and are highly loaded from a thermo-structural point of view. Moreover, modern particle accelerators, storing unprecedented energy, may be exposed to severe accidental events triggered by direct beam impacts. In this context, impulse has been given to the development of novel materials for advanced thermal management with high thermal shock resistance like metal-diamond and metal-graphite composites on top of refractory metals such as molybdenum, tungsten and copper alloys. This paper presents the results of a first-of-its-kind experiment which exploited 440 GeV proton beams at different intensities to impact samples of the aforementioned materials. Effects of thermally induced shockwaves were acquired via high speed acquisition system including strain gauges, laser Doppler vibrometer and high speed camera. Preliminary information of beam induced damages on materials were also collected. State-of-the-art hydrodynamic codes (like Autodyn®), relying on complex material models including equation of state (EOS), strength and failure models, have been used for the simulation of the experiment. Preliminary results confirm the effectiveness and reliability of these numerical methods when material constitutive models are completely available (W and Cu alloys). For novel composite materials a reverse engineering approach will be used to build appropriate constitutive models, thus allowing a realistic representation of these complex phenomena. These results are of paramount importance for understanding and predicting the response of novel advanced composites to beam impacts in modern particle accelerators.

Numerical simulations are now an actual option in order to try to reproduce and understand the mechanical response in components subjected to extreme loading conditions, like in a ballistic impact. A correct materials calibration is therefore necessary in order to extract the materials parameters. In this work the simple and widely used Johnson-Cook model was used to analyse the experimental data obtained for the characterization of the bullet materials. The bullet under investigation is a full metal jacket ball, with a lead-antimony alloy core and a brass jacket. The experimental tests cover a wide range in strain-rate, starting from quasi-static tests up to high dynamic tests performed on a standard Split Hopkinson Pressure Bar setup. In general, there is a great lack in strain-rate sensitivity and failure data. Pure lead is very soft and ductile, so antimony is used to give greater hardness and strength. The results of this study show a significant strain-rate influence for this alloy that can be associated with the presence of the lead-antimony phases and their structures. Also in case of the brass the results showed significant strain-rate sensitivity in the material response.

In the present work a validated numerical approach has been used in order to build a robust and reliable FE model of the impact of a NATO 7.62 mm ball bullet, against an aluminium transmission shaft. The bullet is a full metal jacket type, with a lead alloy core and a brass jacket. Target shaft is made by an Al6061-T6 aluminium alloy. According to the soft core (lead alloy) of the bullet, most effort has been spent in order to evaluate the effect of bullet materials mechanical properties on the numerical results. Numerical analyses, carried out using the non-linear dynamic finite element solver Abaqus∖Explicit 6.10, have been performed focusing on core and jacket material behaviour (target material, Al6061-T6, has been previously calibrated by the authors). Thus numerical analyses have been performed considering for the mechanical behaviour of the bullet both a simplified approach (as reported in literature) and new material data (with strain rate effect) obtained by means of experimental tests on the two materials (lead and brass) with specimens cut directly from the bullet. Finally the results of the analyses have been compared with real experimental ballistic tests.

Syntactic iron foams are produced by metal injection moulding from pure Fe powder and two grades of commercial glass microspheres. Mechanical performance of samples containing 5/10/13 wt% of microspheres is compared to unfilled reference material properties at strain-rates covering 6 orders of magnitude, including Split Hopkinson Pressure Bar (SHPB) experiments. Complex mechanical behavior including strengthening effects of microspheres leading to a plateau strength level which is nearly independent of porosity as well as strain-rate sensitivity of compressive properties are observed. Typical plateau onset stress levels exceed equivalent characteristics of most comparable cellular metallic materials, reaching between approximately 220 and 270 MPa under quasi-static conditions, depending on amount and type of added microspheres. A qualitative explanation of significant events in the deformation sequence as reflected in the stress–strain-curve is offered and discussed in the context of existing studies on syntactic foams. A course for further investigations to verify this hypothesis is suggested.

The main objective of this paper is getting strain-hardening, thermal and strain-rate parameters for a material model in order to correctly reproduce the deformation process that occurs in high strain-rate scenario, in which the material reaches also high levels of plastic deformation and temperature. In particular, in this work the numerical inverse method is applied to extract material strength parameters from experimental data obtained via mechanical tests at different strain-rates (from quasi-static loading to high strain-rate) and temperatures (between 20 °C and 1000 °C) for an alumina dispersion strengthened copper material, which commercial name is GLIDCOP®. Thanks to its properties GLIDCOP® finds several applications in particle accelerator technologies, where problems of thermal management, combined with structural requirements, play a key role. Currently, it is used for the construction of structural and functional parts of the particle beam collimation system. Since the extreme condition in which the material could operate, it is fundamental to characterize it in a wide range both in strain-rate and temperature. The numerical inverse method used in this work is particularly useful to reproduce experimental results when the stress–strain fields in the specimen cannot be correctly described via analytical models. Furthermore this procedure is useful to take into account thermal phenomena generally affecting high strain-rate tests in which the heat conversion of plastic work produces an adiabatic overheating. So, the applicability of this method is particularly indicated in special fields, such as aerospace engineering, ballistic, crashworthiness studies or particle accelerator technologies. The attention is focused on evaluating the most suitable strategy of material model parameters optimization to obtain the best fit between experimental data and numerical results. In this regards, it is important to determine which material model coefficients can be considered as optimization variables and for each of them the most suitable range of variation.

The unprecedented energy intensities of modern hadron accelerators yield special problems with the materials that are placed close to or into the high intensity beams. The energy stored in a single beam of LHC particle accelerator is equivalent to about 80 kg of TNT explosive, stored in a transverse beam area with a typical value of 0.2 mm×0.2 mm. The materials placed close to the beam are used at, or even beyond, their damage limits. However, it is very difficult to predict structural efficiency and robustness accurately: beam-induced damage for high energy and high intensity occurs in a regime where practical experience does not exist. The interaction between high energy particle beams and metals induces a sudden non uniform temperature increase. This provokes a dynamic response of the structure entailing thermal stress waves and thermally induced vibrations or even the failure of the component. This study is performed in order to estimate the damage on a copper component due to the impact with a 7 TeV proton beam generated by LHC. The case study represents an accidental case consequent to an abnormal release of the beam: the energy delivered on the component is calculated using the FLUKA code and then used as input in the numerical simulations, that are carried out via the FEM code LS-DYNA.

In this work, the numerical simulations of the LHC high energy particle beam impact against a metal structure are performed using the commercial FEM code LS-DYNA. The evaluation of thermal loads on the hit material is performed using a statistical code, called FLUKA, based on the Monte-Carlo method, which returns an energy map on a particular geometry (taking into account all the particles in the cascade generated by the interaction between the proton beam and the target). The FLUKA results are then used as input for thermo-structural studies. The first step of this work is the validation of the numerical procedure on a simple geometry for two different materials (copper and tungsten) and constitutive material models. In particular, the high energy particle impact is examined on a facially irradiated cylindrical bar: the beam hits the component directly on the centre of the basis. Then the final step is the study of the impact on a real structure with an energy beam of 5 TeV (the next target in the energy value of LHC beam).

In order to simulate complex scenario like ballistic impact, correct material calibration is fundamental. The material in the area involved by impact can experience high deformation and damage in a very limited time. As a consequence dynamic tests on the materials are needed in order to calibrate constitutive law able to describe the material behavior in terms of hardening and in particular strain rate. According to the fact that no guidelines are available on testing methods, different types of testing techniques have been used to generate data under dynamic conditions. Several dynamic tests, are carried out on Al 6061 T6 specimens and the experimental data elaborated. The developed procedure is useful to take into account also the thermal phenomena generally affecting high strain-rate tests due to the adiabatic overheating related to the conversion of plastic work. The method presented requires strong effort both from experimental and numerical point of view; anyway it allows to precisely identifying the parameters of a material models. This could provide great advantages when high reliability of the material behavior is necessary.

This paper describes a numerical inverse method to extract material strength parameters from the experimental data obtained via mechanical tests at different strainrates and temperatures. It will be shown that this procedure is particularly useful to analyse experimental results when the stress-strain fields in the specimen cannot be correctly described via analytical models. This commonly happens in specimens with no regular shape, in specimens with a regular shape when some instability phenomena occur (for example the necking phenomena in tensile tests that create a strongly heterogeneous stress-strain fields) or in dynamic tests (where the strain-rate field is not constant due to wave propagation phenomena). Furthermore the developed procedure is useful to take into account thermal phenomena generally affecting high strain-rate tests due to the adiabatic overheating related to the conversion of plastic work. The method presented requires strong effort both from experimental and numerical point of view, anyway it allows to precisely identify the parameters of different material models. This could provide great advantages when high reliability of the material behaviour is necessary. Applicability of this method is particularly indicated for special applications in the field of aerospace engineering, ballistic, crashworthiness studies or particle accelerator technologies, where materials could be submitted to strong plastic deformations at high-strain rate in a wide range of temperature. Thermal softening effect has been investigated in a temperature range between 20°C and 1000°C.

The introduction in recent years of new, extremely energetic particle accelerators such as the Large Hadron Collider (LHC) gives impulse to the development and testing of refractory metals and alloys based on molybdenum and tungsten to be used as structural materials. In this perspective, in this work the experimental results of a tests campaign on Inermet® IT180 and pure Molybdenum (sintered by two different producers) are presented. The investigation of the mechanical behaviour was performed in tension varying the strain-rates, the temperatures and both of them. Overall six orders of magnitude in strain-rate (between 10−3 and 103 s−1) were covered, starting from quasi-static up to high dynamic loading conditions. The high strain-rate tests were performed using a direct Hopkinson Bar setup. Both in quasi-static and high strain-rate conditions, the heating of the specimens was obtained with an induction coil system, controlled in feedback loop, based on measurements from thermocouples directly welded on the specimen. The temperature range varied between 25 and 1000°C. The experimental data were, finally, used to extract the parameters of the Zerilli-Armstrong model used to reproduce the mechanical behaviour of the investigated materials.