Daniele Forni

• Doctor of Philosophy
• University of Applied Sciences and Arts of Southern Switzerland

Climate change is intensifying severe weather events, especially in alpine environments where hailstorms are more frequent and intense. In particular, hail damage seriously affects photovoltaic systems. The severity of hailstorms as well as impact responses are important factors in mitigating loss, so the first research area that needs to be addres...

In this paper, a commercial tungsten alloy is investigated in dynamic tensile tests with high strain rates and elevated temperatures on smooth and notched specimens. A Split Hopkinson Tensile Bar device, equipped with a water-cooled induction heating system, was used to perform the tests at high strain rates and elevated temperatures on round speci...

This paper describes the comparison between compressive behaviour of a commercial Ultra High-Performance (Fibre-Reinforced) Concrete, having 3% content of high carbon straight steel fibres, and its matrix. A special device named 3D-Modified Hopkinson Bar (3D-MHB) installed in the DynaMat SUPSI Laboratory was used to test cylindrical specimens with...

The design of structures that can withstand dynamic loads requires a deep understanding of the dynamic behaviour of materials. Natural events (hurricanes, earthquakes, snowslides, rockfalls, floods, tsunami) or human or accidental actions (impact, blast) can trigger these types of action. The Kolsky bar (or split Hopkinson bar) is universally recog...

The effects of elevated temperature and high strain rate on S690QL high strength steel material properties are described. These data are meaningful for the design and structural safety assessment of critical artefacts (bridges, cranes, offshore structures) under combined extreme loadings (impact and explosion) and temperature conditions (fire). Tes...

In this study, we used a Modified Hopkinson bar and a hydro-pneumatic machine to characterize the behaviour of 3D-printed concrete elements under different stress rates, focusing on the interface behaviour between consecutive layers under different loading conditions and in various significant, dynamic regimes. The paper includes the results of dyn...

The restoration of Inconel 718 components through conventional processes typically require cost-intensive machining operations. Moreover, the refurbishment and reuse are extremely important in structural components likely to be subjected to harsh operating conditions (dynamic loads and elevated temperatures). That is why additive manufacturing proc...

Strain-hardening cement-based composites (SHCC) represent a special type of fiber reinforced concretes, whose post-elastic tensile behavior is characterized by the formation of multiple, fine cracks under increasing loading up to failure localization. The high inelastic deformability in the strain-hardening phase together with the high damage toler...

Within their lifetime, reinforced concrete structures can be subjected to extreme loadings such as fire and blast, which are often combined or occur in sequence. Frequently, a fire within a structure causes internal blasts, leading to catastrophic damages and sometimes may be the main cause of the triggering of progressive collapses. Thus, it appea...

In the last years, powder-based Laser Metal Deposition (LMD) has been attracting attention as a disruptive Additive Manufacturing (AM) technique for both the fabrication and restoration of Inconel 718 components, enabling to overcome current limitations faced by conventional manufacturing processes in terms of manufacturing costs, tool wear, and le...

Nickel-based superalloys are widely used in critical applications where structural components are subjected to harsh operating conditions such as elevated temperatures and high strain-rate. These alloys are also among the most hard-to-cut materials. For this reason, some critical components with complex geometrical features along with critical dime...

The effects of elevated temperature at high strain rate of a commercial tungsten alloy were investigated. The tests were carried-out at high strainrate (from 850 to 2200 1/s) by means of a Split Hopkinson Tension Bar device on round specimens having diameter and gauge length of 2mm and 5 mm, respectively. The thermal conditions were obtained by mea...

Understanding the dynamic response of Ultra-High Performance Fibre-Reinforced Concrete has important implications for engineering applications, including protective structures and critical infrastructures. It is wellknown that the loading rate affects both material failure mechanism and mechanical properties such as strengths and absorbed energy. M...

In order to properly design critical infrastructures and buildings in steel (bridges, high-rise building, off-shore, cranes, etc.), certain requirements concerning to mechanical resistance and robustness under exceptional actions have to be carefully fulfilled. An acceptable level of safety must be assured to avoid human loss, environmental polluti...

In concrete structures realized by digital fabrication techniques, such as 3D concrete printing, under severe dynamic loadings (e.g. earthquakes and impact loads), the strength at the bond interfaces between layers is weak. Since these contact zones, also referred as cold joint, could potentially compromise the structural stability and also the dur...

High Strength Steels are increasingly demanded in building constructions, shipbuilding and other industries. Hard impact and explosion are possible hazards for steel structures as high-rise buildings, bridges, ships, off-shores. Present lack of data sets under high strain-rates might be generate uncertainty in structural assessment under severe dyn...

Recently, the interest in digital fabrication techniques, such as 3D concrete printing, has grown at a dizzying speed, but at the same time many critical issues are still wide-open. Weak strength at the bond interface of two concrete layers, also referred as cold joint, is one such critical task to be scientifically investigated, especially in depe...

An experimental investigation was carried out to characterise the direct tensile behaviour at high strain rate of various UHPFRC mix designs (150, 170 and 210 MPa) with various dosages of fibres. The mechanical characterisation at high strain-rate was performed by means of two split Hopkinson tension bar devices and one Hydro-Pneumatic Machine that...

Tungsten alloys are often used in machinery and in other industrial sectors. This study presents the dynamic tensile behaviour of a commercial tungsten alloy. The tests were carried-out at high strain-rate (from 850 to 2200 s_1) by means of a Split Hopkinson Tension Bar device on round specimens having diameter and gauge length of 2 mm and 5 mm, re...

The comprehension of the phenomena caused by fast-transient-loading regimes on structures, such as impact or blast, plays a capital role in order to prevent catastrophic failures. In fact, very complex failure modes can occur at these regimes where compression, tensile and shear strengths are involved. The present study investigates the dynamic res...

The lack of full stress-strain data sets under the coupled effect of high strain rates and elevated temperatures is one of the main concerns in a multi-hazard (blast and fire) approach of very-high strength steel (VHSS) structures. The main research challenge is represented by the assessment of the strain rate behaviour in tension and in a wide ran...

The use of stainless steel rebars is required when reinforced concrete structures are subjected to harsh environmental conditions during their lifetime. Some special infrastructures in addition to these climatic factors can be also subjected to extreme limit states of loading and temperature as in the case of fire followed by blast. This study deal...

Two different types of strain-hardening cement-based composites (SHCC) were investigated under uniaxial quasi-static and impact tensile loading. The normal-strength matrix was combined with polyvinyl-alcohol (PVA) fiber in one composite and with high-density polyethylene (HDPE) fiber in another. A modified Hopkinson bar was used to assess the impac...

Understanding the response of the building materials under extreme condition of loading (blast and impact events) and temperature (fire) is fundamental for civil engineers to design safe structures for civil or defense applications. In this paper an experimental investigation on the influence of the combined effects of high strain rate and elevated...

This paper presents a comparison between mechanical compressive and tensile properties of S355 structural (mild) steel in a wide range of strain rates. A split Hopkinson pressure bar apparatus is used to investigate the dynamic compressive behaviour at high strain rates (740–5880 s⁻¹). A hydro-pneumatic machine (5–25 s⁻¹) and a modified split Hopki...

The advantages of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) under static loads suggest it is a promissory material to withstand dynamic and especially extreme loads. However, the available results concerning dynamic behaviour of UHPFRC under high strain rates are still rather limited and there are some aspects that require further a...

The paper presents a part of a full-experimental campaign characterizing various Ductal® mix designs (compressive strength of 150, 170, 210MPa) with various dosages of fibers (2% and 3.25%). The dynamic tests are performed by means of two Modified Hopkinson Bar devices with that are installed at the DynaMat Laboratory in Lugano. The tests, in tensi...

The dynamic behaviour of earthen materials reinforced with natural fibres is little studied although earth buildings are often built in seismic areas. In this paper the dynamic behaviour of an earthen material reinforced with hemp fibres under different impact loadings has been experimentally investigated. The dynamic response of the material in 3-...

In this paper, dynamic behaviour of fiber reinforced mortars manufactured with innovative binders based on calcium sulphoaluminate cement (CSA), supplementary cementitious materials (SCMs), gypsum (G) and hydrated lime (CH) was investigated. Fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used to develop sustainable Portland-free...

The paper presents a part of an experimental campaign consisting of quasi-static and impact tensile experiments on three different types of strain-hardening cement-based composites (SHCC) as well as on their constitutive cementitious matrices [1]. The investigation on different SHCC types was intended for analysing the effect of matrix composition...

The paper presents the results obtained on cylindrical Ultra High Performance Fibre Reinforced Concrete specimens with diameter of 30mm and a height of 60mm under compression at high stress rate (1.7–2.3 TPa/s). Four different percentages of fibre reinforcement are considered (1, 2, 3, and 4% fibre content) and compared with the results of the matr...

The use of aluminium alloys in the construction of defence vehicles is strongly increasing in these last decades due to their comparably promising potential of the weight-performance relationship at similar price range. In this paper, the mechanical properties at high strain rate in tension of several commercial aluminium (2xxx, 5xxx, and 7xxx) all...

The paper presents a part of a full-experimental campaign characterizing various Ductal ® mix designs (150, 170, 210MPa) with various dosages of fibers. The mechanical characterization at high strain-rate is performed by means of two Modified Hopkinson Bar devices and one Hydro-Pneumatic Machine that are installed at the DynaMat Laboratory of the U...

Detailed finite element modelling of key elements is necessary to improve the robustness assessment of structures subjected to a coupled effect of fire and blast loads. This paper presents a method for a realistic multi-hazard approach by studying the residual load bearing capacity of steel columns under fire conditions and followed by an explosion...

Three different types of strain-hardening, cement-based composites (SHCC) as well as their constitutive cementitious matrices were investigated under uniaxial quasi-static and impact tensile loading. The normal-strength matrix was combined with polyvinyl-alcohol (PVA) fiber in one composite and with high-density polyethylene (HDPE) fiber in another...

The use of aluminium alloys in the construction of defense vehicles is strongly increasing in these last decades because they require new lightweight armours for improving their survivability without sacrificing efficiency and performance. In this paper the effects of strain rate on the mechanical properties in tension of a commercial aluminium all...

The performance of reinforced concrete structures under combined effects of blast and fire is growing in interest of the research and engineering communities specially after the recent terrorist attacks as well as severe accidents (i.e. Gotthard tunnel, etc.). The mechanical behaviour of concrete and reinforcing steel when are subjected to extreme...

This paper presents the strain rate behaviour in tension of the S355 structural steel using a modified Split Hopkinson Tensile Bar for the mechanical characterisation at high strain rates (300 , 500 and 850 ), and a Hydro Pneumatic Machine for intermediate strain rates (5 and 25 ). These data are collected with the intention of setting down the bas...

The results of experimental investigation on the tensile response of UHPFRCs under high stress rates are presented. The dynamic tests are carried out on notched cylindrical specimens using a Split Hopkinson Tensile Bar. The material behavior of UHPFRC and its matrix (UHPC) is investigated at four high stress rates (from 400 to 1000 GPa/s). The rate...

This paper presents an experimental investigation on the strain rate sensitivity of Dual Phase steel 1200 (DP1200) and Dual Phase steel 1400 (DP1400) under uni-axial tensile loads in the strain rate range from 0.001 s−1 to 600 s−1. These materials are advanced high strength steels (AHSS) having high strength, high capacity to dissipate crash energy...

In this paper, the dynamic behaviour of cement mortars reinforced with both glass and basalt fibres is studied. The influence of the addition of both types of fibre on energy absorption and tensile strength at high strain-rate was investigated, and the performance of the two types of fibre-reinforced mortar was compared. For this aim, basalt and gl...

In this paper the high strain rate behaviour in tension and in a wide range of elevated temperatures of the S355 structural steel is presented. A Split Hopkinson Tensile Bar for the mechanical characterisation at high strain rates, equipped with a water-cooled induction heating system is used. These data are collected with the purpose of evaluating...

It is unquestionable the fact that a structural system should be able to fulfil the function for which it was created, without being damaged to an extent disproportionate to the cause of damage. In addition, it is an undeniable fact that in reinforced concrete structures under severe dynamic loadings, both concrete and reinforcing bars are subjecte...

Geopolymers are a promising class of inorganic materials typically obtained from an alluminosilicate source and an alkaline solution, and characterized by an amorphous 3-D framework structure. These materials are particularly attractive for the construction industry due to mechanical and environmental advantages they exhibit compared to conventiona...

The objective of this study was to investigate the compression behaviour of the UHPFRC and its matrix (UHPC) under high strain rate. Two experimental set-ups were used for compression testing: a traditional Split Hopkinson Pressure Bars and a compression version of the Modified Hopkinson Bar. The tests were conducted, in the range of 100–500 s−1 on...

In order to study the dynamic behaviour of material in confined conditions a new machine was conceived and called 3D-Modified Hopkinson Bar (3D-MHB). It is a Modified Hopkinson Bar apparatus designed to apply dynamic loading in materials having a tri-axial stress state. It consists of a pulse generator system (with pre-tensioned bar and brittle joi...

This paper presents an experimental investigation on the influence of the temperature on the reduced activation steel Eurofer97 under uniaxial tensile loads at high strain rate. Round undamaged specimens of this material having gauge length 5 mm, diameter 3 mm, were tested in universal machine to obtain its stress-strain relation under quasi-static...

In this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar...

The dynamic behaviour of armour steel in tension was investigated over a wide range of strain-rates on round specimens. The experiments were carried out by means of a Split Hopkinson Tensile Bar device and by a Hydro Pneumatic Machine. The target strain rate were set at the following six levels: 10−3, 5, 25, 100, 500 and 1000 s−1. Two material mode...

The mechanical behaviour of bones when subjected to tension loading in a wide range of strain-rates is fundamental to develop protection systems. The paper presents the preliminary tests on the tensile behaviour of bovine cortical bone at medium and high strain rates. Two special apparatus, both installed at the DynaMat Laboratory of the University...

The paper presents two identification methods of parameters for the Johnson-Cook constitutive equation. The Johnson-Cook equation is one of the most popular semi-empirical constitutive models to describe the equivalent of plastic stress-strain curves. The first presented method is the approximation method of plastic hardening stress-strain curves,...

In reinforced concrete structures under severe dynamic loading, as impact and blast, both concrete and reinforcing bars are subjected to high strain- rates. While the dynamic tensile behaviour of concrete is the subject of many researches, the behaviour of the reinforcing steel under high strain rate has been not completely considered yet. Such beh...

The results of an experimental research on the uniaxial tension behaviour of quenched and self-tempered reinforcing steel (grade B450C Tempcore rebar) at high strain rate are presented. Quenched and self-tempered rebar is considered to be a composite bar made of a hardened outer layer, an intermediate hardened layer and a soft inner core. The effec...

The behaviour under impact loading of stainless steels used for reinforcing bars is studied. Therefore, the effect of strain rate on AISI304 stainless steel was investigated. Tensile tests on round specimens at different strain-rate levels (high, intermediate and quasi-static) were performed. Stress–strain relationships under different strain-rate...

The paper presents the dynamic characterization in tension and compression of three rocks, Carrara marble, Onsernone gneiss and Peccia Marble, at high strain-rates. Two versions of a Split Hopkinson Bar have been used. The version for direct tension tests is installed at the DynaMat Laboratory of the University of Applied Sciences of Southern Switz...

In this paper the preliminary results of the tensile behavior of reinforced steel in a large range of strain rates are presented. Tensile testing at several strain rates, using different experimental set-ups, was carried out. For the quasi-static tests a universal electromechanical testing machine with the maximum load-bearing capacity of 50 kN was...

Advanced researches on concrete are directed toward investigating the behavior of reinforced concrete structures in severe conditions such as those promoted by impact loads. Some particular structures (protective shelters, nuclear reactor containment, offshore structures, military structures, chemical or Energy production plant) may be subjected to...

In this paper the first results of the mechanical characterization in tension of two high strength alloys in a wide range of strain rates are presented. Different experimental techniques were used for different strain rates: a universal machine, a Hydro-Pneumatic Machine and a JRC-Split Hopkinson Tensile Bar. The experimental research was developed...

The tensile properties of the high-chromium tempered martensitic reduced activation steel Eurofer97 were determined from tests carried out over a wide range of strain-rates on cylindrical specimens. The quasi-static tests were performed with a universal electro-mechanical machine, whereas a hydro-pneumatic machine and a JRC-split Hopkinson tensile...

Owner: Ezio, Added to JabRef: 2011.07.20

Owner: Ezio, Added to JabRef: 2011.05.14

The mechanical properties in tension of two aluminium alloys (AA5059-H131 and AA7039-T651) used in armour applications were determined from tests carried out over a wide range of strain-rates on round specimens. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The targe...

The paper presents the dynamic characterization in tension of three rocks under medium and high strain rates. The tests have been carried out by means of the JRC-Split Hopkinson Tension Bar and an Hydro-Pneumatic Machine installed in the DynaMat Laboratory of the University of Applied Sciences of Southern Switzerland. The dynamic direct tension tes...

Experimental results on three types of HPFRCC reinforced with steel and polyvinyl-alcohol fibres subjected to dynamic tensile loading are presented. The tests were carried out on notched-specimens by means of a modified Hopkinson bar, a hydro pneumatic and universal apparatus for high, medium and low strain-rate respectively. From the experiments i...

Owner: Ezio, Added to JabRef: 2009.11.10

The optimum design of rockfall protective shelters resistant to quasi-static, strong earthquake and impact loading, requires the use of modern computer codes implemented with the consti-tutive equations developed and calibrated on the mechanical properties of the materials; they should be measured with precision tests in a large range of strain rat...

Owner: Ezio, Added to JabRef: 2009.11.11