Numerical and experimental study on mechanical behaviour of the AlSi10Mg aluminium structures manufactured additively and subjected to a blast wave

The paper is related to energy absorptive properties of additively manufactured metallic cellular structures. The samples of Honeycomb, Auxetic, rhomboidal Lattice and a regular Foam are subjected to a dynamic compression due to the blast tests. The cuboidal samples are manufactured by the Direct Metal Laser Sintering (DMLS) method using AlSi10Mg aluminium powder. The experimental tests are performed by means of an Explosive Driven Shock Tube (EDST). The measured results of the transmitted forces in relation to the shortening of the samples allow to analyse the deformation processes of each selected geometry. In addition, the evaluation of the structural responses leads to identification of the structure properties, such as the equivalent stress over equivalent strain or the energy absorption per a unit of mass. Moreover, the process of compression is modelled numerically using the explicit code LS-DYNA R9.0.1. The obtained simulations provide the complete analysis of the experimentally observed mechanisms.

Dynamic testing and simulation of 9 mm full metal jacket ammunition

Ballistic protection for armed forces requires a continuous performance improvement to successfully face ever evolving threats and scenarios. Ballistic tests are conventionally carried out in order to assess and validate the levels of protection to a high degree of accuracy. Although very effective, those tests are often time consuming and lack the necessary flexibility. A better approach would be to set up a numerical protocol for a number of simulations and only carry out final real life validation tests. Unquestionably, the main advantage of finite element modelling is the possibility to simultaneously evaluate a wide variety of configurations and their interactions (materials, geometry, architecture, etc.). For reliability, it is necessary to use sufficiently precise material behaviour models to accurately transcribe the phenomena observed during the impact. Our study focuses on the mechanical behaviour of 9 mm ammunition materials, namely a lead alloy core and a steel alloy jacket. For this purpose, a preliminary study (not presented here), was carried out on both the lead core and the steel jacket separately and the parameters for each constitutive model were determined. Lead-steel cylindrical samples, extracted from the ammunition, have been used for the validation of the entire constitutive model. By utilizing those samples, a high degree of the ammunitions material properties have been retained. SHPB tests have been carried out in multiple conditions, varying the striker speeds and temperatures. Additionally, the tests were recorded with an ultra-high speed camera. Strain gages were used to record signals along the input and output bars. Those measurements have been compared to numerical results using Finite Element code (ABAQUS® Explicit). A very satisfying correlation between the experimental data and the simulation has been reached, thus validating the jacket and core constitutive models and interactions for subsequent studies of ballistic impacts.

Mechanical Properties of Brass under Impact and Perforation Tests for a Wide Range of Temperatures: Experimental and Numerical Approach

The originally performed perforation experiments were extended by compression and tensile dynamic tests reported in this work in order to fully characterize the material tested. Then a numerical model was presented to carry out numerical simulations. The tested material was the common brass alloy. The aim of this numerical study was to observe the behavior of the sample material and to define failure modes under dynamic conditions of impact loading in comparison with the experimental findings. The specimens were rectangular plates perforated within a large range of initial impact velocities V₀ from 40 to 120 m/s and in different initial temperatures T₀. The temperature range for experiments was T₀ = 293 K to 533 K, whereas the numerical analysis covered a wider range of temperatures reaching 923 K. The thermoelasto-viscoplastic behavior of brass alloy was described using the Johnson–Cook constitutive relation. The ductile damage initiation criterion was used with plastic equivalent strain. Both experimental and numerical studies allowed to conclude that the ballistic properties of the structure and the ballistic strength of the sheet plates change with the initial temperature. The results in terms of the ballistic curve V_R (residual velocity) versus V₀ (initial velocity) showed the temperature effect on the residual kinetic energy and thus on the energy absorbed by the plate. Concerning the failure pattern, the number of petals N was varied depending on the initial impact velocity V₀ and initial temperature T₀. Preliminary results with regard to temperature increase were recorded. They were obtained using an infrared high-speed camera and were subsequently compared with numerical results.

Machinability of INCONEL718 Alloy with a Porous Microstructure Produced by Laser Melting Powder Bed Fusion at Higher Energy Densities

Products produced by additive manufacturing (AM) seek to exploit net shape manufacturing by eliminating or minimizing post-process stages such as machining. However, many applications which include turbo machinery components with tight dimensional tolerances and a smooth surface finish will require at least a light machine finishing stage. This paper investigates the machinability of the additively fabricated INCONEL718 (IN718) alloy produced by laser melting powder bed fusion (LM-PBF) with different levels of spherical porosity in the microstructure. The literature suggests that the band width for laser energy density, which combines the various scan process parameters to obtain a low spherical type porosity in the LM-PBF IN718 alloy (~1%), has wide breadth. With the increasing laser energy density and above a threshold, there is a rapid increase in the spherical pore size. In this paper, three tube samples each with different levels of spherical porosity were fabricated by varying the laser energy density for LM-PBF of the IN718 alloy within the stable and higher energy density range and the porosity measured. A low laser energy density was avoided due to balling up, which promotes highly irregular lack of fusion defects and poor consolidation within the alloy microstructure. An orthogonal turning test instrumented, with a three-component dynamometer to measure the cutting forces, was performed on AM produced IN718 tube samples under light cut conditions to simulate a finish machining process. The orthogonal turning tests were also performed on a tube sample obtained from the wrought extruded stock. The machining process parameters, which were studied include varying the cutting speed at three levels, at a fixed feed and under dry cut conditions for a short duration to avoid the tool wear. The results obtained were discussed and a notable finding was the higher rate of built-up-edge formation on the tool tip from the AM samples with a higher porosity and especially at a higher cutting speed. The paper also discusses the mechanisms that underpin the findings.

Experimental and Numerical Study of the Thermo-Viscoplastic Behavior of NICRO 12.1 for Perforation Tests

Dynamic impact tests using thin metal plates for ballistic characterization have received significant attention in recent years. The Johnson–Cook (J–C) model is extensively used in numerical modeling of impact and penetration in metals. The AISI (American Iron and Steel Institute) 301 steel family presents good impact behavior, excellent formability, and high corrosion resistance. Thus, NICRO (Nickel and Hard Chrome Plated Steel) 12.1 (part of the AISI 301 steel family) was chosen in this work, although parameters of the J–C model or impact results were not found in the literature. In this work, NICRO 12.1 steel plates, were characterized in ballistics with an initial impact velocity up to 200 m/s and three shape nose projectiles. The Johnson–Cook parameters for the NICRO 12.1 steel were calculated for a large range of temperatures and strain rates. Impact tests were carried out using three projectiles: conical, hemispherical, and blunt. The ballistic curves, failure mode, and maximum deformation obtained with each projectile, experimentally and numerically, were compared, and a good correlation was obtained.

Characterization of the Mechanical Behavior of a Lead Alloy, from Quasi-Static to Dynamic Loading for a Wide Range of Temperatures

The current needs in terms of ballistic protection for armed forces require an almost constant improvement in performance to face the constantly evolving threats and scenarios. Ballistic tests are conventionally carried out in order to assess and validate the levels of protection. The challenge is to be able to set up a digital protocol and only carry out final validation tests. Indeed, the advantage of digital simulation lies in the possibility of being able to evaluate a wide variety of configurations. In order to obtain reliable results, it is necessary to use sufficiently precise material behavior models to transcribe the phenomena observed during the impact. Our study focuses on the behavior of a small caliber ammunition with a ductile core impacting personal protection. More particularly on the mechanical behavior of the lead alloy core. Thus, compression tests have been carried out on a wide range of deformation rates, from quasi-static behavior to dynamic regime, at different temperatures. The study in dynamic conditions was carried out using split Hopkinson pressure bars. Due to the material properties, the experimental device had to be adapted in order to optimize the propagation of the waves allowing to measure signals (elastic waves). These tests demonstrate the dependency of the stress with strain rate and temperature. Dynamic restoration and recrystallization phenomena, characteristic of a material deformed in its hot working area, have also been identified. The associated oscillations due to Pochhammer–Chree effect, observable on the stress–strain curves, constitute the major problem for the implementation of behavioral models. Finally, a constitutive model sensitive to strain rate and temperature is investigated for ballistic purposes.

Constitutive Models for Dynamic Strain Aging in Metals: Strain Rate and Temperature Dependences on the Flow Stress

A new constitutive model for Q235B structural steel is proposed, incorporating the effect of dynamic strain aging. Dynamic strain aging hugely affects the microstructural behavior of metallic compounds, in turn leading to significant alterations in their macroscopic mechanical response. Therefore, a constitutive model must incorporate the effect of dynamic strain aging to accurately predict thermo-mechanical deformation processes. The proposed model assumes the overall response of the material as a combination of three contributions: athermal, thermally activated, and dynamic strain aging stress components. The dynamic strain aging is approached by two alternative mathematical expressions: (i) model I: rate-independent model; (ii) model II: rate-dependent model. The proposed model is finally used to study the mechanical response of Q235B steel for a wide range of loading conditions, from quasi-static loading ( ε ˙ = 0.001   s - 1 and ε ˙ = 0.02   s - 1 ) to dynamic loading ( ε ˙ = 800   s - 1 and ε ˙ = 7000   s - 1 ), and across a broad range of temperatures ( 93   K - 1173   K ). The results from this work highlight the importance of considering strain-rate dependences (model II) to provide reliable predictions under dynamic loading scenarios. In this regard, rate-independent approaches (model I) are rather limited to quasi-static loading.

Material Characterization of PMC/TBC Composite Under High Strain Rates and Elevated Temperatures

Polymer matrix composites (PMC), despite their many advantages, have limited use at elevated temperatures. To expand the scope of their uses, it becomes necessary to use thermal barrier coatings (TBC). In addition to elevated temperatures, composite structures, and thus TBC barriers, can be exposed to damage from impacts of foreign objects. Therefore, before using the thermal barrier in practice, knowledge about its behavior under high-speed loads is necessary. The paper presents results for samples with the PMC/TBC system subjected to dynamic compression using a split Hopkinson pressure bar (SHPB). The substrate was made of CFRP (carbon reinforced polymer) with epoxy matrix and twill fabric. TBC was made of ceramic mat saturated by commercial hardener from Vitcas company. The tests were carried out at ambient temperature and elevated temperature—55 °C and 90 °C. Tests at ambient temperature were carried out for three pressure levels: 1, 1.5, and 2 bar. Only the pressure of 1 bar was used for the elevated temperature. Studies have shown that the limit load is 1 bar for ambient temperature. At 1.5 bar, cracks occurred in the TBC structure. Increased temperature also adversely affects the TBC barrier strength and it is damaged at a pressure of 1 bar.

Mechanical behaviour modelling under dynamic conditions: Application to structural and high strength steels

Current needs in the design and optimization of complex ballistic protection structures lead to the development of more and more accurate numerical modelling for high impact velocity. The aim of developing such a tool is to be able to predict the protection performance of structures using few experiments. Considering only numerical approach, most important issue to have a reliable simulation is to focus on material behaviour description in term of constitutive relation and failure model for high strain rates, large field of temperatures and complex stress states. In this context, the study deals with the behaviour of two steels including a high strength steel and a structural steel. For this application, the materials can undergo both quasi-static and dynamic loading. Thus the strain rate range studied is varying from 10−3 to more than 103 s−1. Although the high strength steels do not exhibit high strain rate sensitivity, the temperature increases during dynamic loading is inducing thermal softening. Thus, temperature sensitivity is defined up to 500 K under quasi-static and dynamic conditions. Then, experiments are used to define the parameters of several constitutive relations like the Johnson-Cook model or the Rusinek Klepaczko model.

Dynamic perforation and compression tests of PMMA for a wide range of temperatures - experimental and preliminary numerical analysis

Experimental tests were carried out on poly(Methyl Methacrylate) (PMMA) in order to define its mechanical behaviour over a wide range of temperature. To reach high strain rate, perforation tests were performed within a wide range of temperatures using a high-performance oven, from room temperature to 130 °C, above the glass transition temperature Tg. In addition, the results were confronted with compression tests previously obtained. Based on experiments, the temperature transition between fragile and ductile was defined. The material became fully ductile above 118 °C inducing no cracking and debris during the perforation process. The yield stress evolution as function of strain rate for various temperatures was modelled by using the cooperative model. The model predictions were in agreement with experimental data. Two material models developed by Richeton and Nasraoui were analysed, the latter was then implemented into the FE model to simulate perforation tests for a wide range of temperatures and strain rates. It was observed that the coupling strain rate-temperature is a key factor to predict the structure behaviour not only in terms of material behaviour but also in terms of dynamic failure.

Morphology of the first instar of Calliphora vicina, Phormia regina and Lucilia illustris (Diptera, Calliphoridae)

Scanning electron microscopy documentation of first instar Calliphora vicina Robineau-Desvoidy, Phormia regina (Meigen) and Lucilia illustris (Meigen) (Diptera: Calliphoridae) is presented for the first time, and the following morphological structures are documented: pseudocephalon; antenna; maxillary palpus; facial mask; labial lobe; thoracic and abdominal spinulation; spiracular field; posterior spiracles, and anal pad. Light microscopy documentation and illustrations are provided for the cephaloskeleton in lateral and ventral views. New diagnostic features are revealed in the configuration of the facial mask, cephaloskeleton and posterior spiracles. The first instar morphology of C. vicina, Ph. regina and L. illustris is discussed in the light of existing knowledge about early instars of blowflies.

[Microbiological evaluation of ciprofloxacin efficacy for treatment of urinary tract infections]

An attempt has been undertaken to evaluate the aetiology of urinary tract infections in a large group of patients and to determine the resistance to ciprofloxacin during therapy, and the efficacy of the drug in treating of urinary tract infections. 52 patients with urinary tract infections were treated with ciprofloxacin. Ciprobay by BAYER was used in coated 500 mg tablets twice a day and intravenous solutions in 200 mg dosages every 12 hours for 10-14 days depending on the clinical condition. Microbiological tests were made according to general methods. Sensitivity evaluation to ciprofloxacin was done using E-tests by AB Biodisk and dilution tests. The most common a etiology of urinary tract infections were Gram-negative Enterobacteriaceae rods, mainly E. coli. Ciprofloxacin gave the best results against Enterobacteriaceae rods (100% eradications). In other infections, effective therapy was possible after determining of the sensitivity in vitro. S. haemolyticus bacteria tended significantly towards resistance to ciprofloxacin during therapy.