Threaded links are widely used in many structures designed to sustain extreme dynamic loads. Therefore, investigation of their behavior under such extreme conditions is crucial. A recent review highlighted a significant gap in understanding the mechanical behavior of threads under impact loads [Warren et al. J Constr Steel Res, 2022;194]. Therefore, this study investigates the effect of thread geometries on stress waves propagating through the threads using two parallel approaches: experimental and numerical simulations. Different threads were manufactured from steel alloys with varying lengths of pitch and tooth geometries. Experiments using a split Hopkinson pressure bar (SHPB) system and a numerical simulation using the LS-DYNA code were performed to characterize the propagation of a stress wave when crossing different threads. The investigation revealed that increasing the tooth height of the threads and the number of teeth reduced the distortion of stress waves produced by the thread. It was also shown that a fine thread could reduce the level of the transmitted stress under dynamic loading, similar to the effect observed when using a porous material. With this feature, it will be possible to design thread connections with the ability to mitigate or transmit dynamic impulse loads.

This study deals with additive manufacturing (AM) products. Employing AM technology, complex-shaped, and lightweight parts can be fabricated using the aluminum alloy, AlSi10Mg. Typically, AM of this alloy is performed by laser powder bed fusion (LPBF). The mechanical properties of LPBF products are crucial for many engineering applications. Therefore, there have been efforts to measure the dynamic and quasi-static properties of such products. However, both the dynamic and quasi-static shear behaviors of this alloy are yet to be investigated. The present study is focused on experimentally investigating the shear behavior of LPBF AlSi10Mg. ‏Quasi-static shear tests were performed according to the ASTM B565 protocol, whereas dynamic shear tests were conducted using a standard split Hopkinson pressure bar equipped with an innovative sample holder that generates pure shear in a sample. The results of the performed tests showed that as the shear load rate increased, the shear strength considerably increased. In addition, in the quasi-static regime, the shear strength was practically independent of the product build direction. In contrast, under the dynamic shear conditions, samples built horizontally failed at a shear strength approximately 10% lower than that of those manufactured vertically. To investigate the build orientation effect on the shear behavior, this study conducted extensive microstructural characterization along with fracture analysis. Crack nucleation and propagation were analyzed in view of the effects of the unique microstructural characteristics of the LPBF AlSi10Mg, including the morphologies of the melt pool boundaries. The results obtained in this study suggested that for engineering applications in which dynamic loads are expected, the build orientation of AlSi10Mg parts produced using LPBF technology must be considered.

Additive manufacturing by selective laser melting (AM-SLM) is an advanced manufacturing approach in which a structure is fabricated by successive thin powder layers melted by a focused laser beam. The aerospace and automotive sectors are especially interested in the AMSLM technology that enables quick production of complex and customized structures. AlSi10Mg alloy has been found to be applicable to AM-SLM mainly because good cast-ability, strong weldability and low shrinkage during solidification. While many studies on the quasi-static mechanical properties and the structure of SLM AlSi10Mg were published, there is limited published research focused on the dynamic properties of SLM AlSi10Mg under high rate strains. In addition to that, the shear strength of SLM aluminium alloys is rarely investigated. This study presents an investigation of the AM-SLM AlSi10Mg static and dynamic shear strength and its dependency on build direction. Experiments included quasi-static shear experiments performed according to the protocol of ASTM B565, and dynamic shear tests performed using a split Hopkinson pressure bar (SHPB), coupled to innovative punch assembly that generates pure dynamic shear loads on the sample. The design of this sample holder has been validated numerically and an experimentally. The quasi-static experiments revealed that the static shear strength is independent of build direction. In contrast, the dynamic tests demonstrated that the dynamic shear strength of vertically built samples is higher by almost 11% than the shear strength of samples built horizontally. This last phenomenon explained with a suggested mechanism based onelectron microscope fractography.

In spite of the worldwide recognition of the importance of testing blast effects on dummy humans, there is a lack of blast simulators that are capable of generating realistic blast conditions in the laboratory. The objective of the present study was to design, construct and test a blast tube that is able to accurately reproduce loading histories of actual explosions in the laboratory. The design combines some advantages of existing blast-wave generating facilities. Using numerical simulations, a 5-m long blast tube was designed. The blast tube is large enough to enclose dummies including torso and head, wearing vests and/or helmets. The system generated blast waves equivalent to those of a spherical explosion of about 3.5 kg TNT with an over pressure of 0.64 bar and a positive phase of 4 ms. The repeatability of the experiments was very good. The blast tube’s open end is square of 1.57 m × 1.57 m and although designed for experiments on human dummies, it could be used for testing even full-scale structural components. High quality high-speed photography was demonstrated through the designed windows. Our preliminary study on the effect of a helmet on a dummy’s head revealed that the tested helmet amplified by a factor of 2 and more the peak pressure in the back side of the head. The newly designed blast tube is capable of simulating close range blast waves, manifested with short positive durations. Experiments with and without helmets revealed the importance of blast testing for improving helmet design.

•A unique design for a vertical tension split Hopkinson bar with steel bars and an aluminum hammer.•Direct tension applied to concrete samples.•Numerical simulations performed of all tests conducted with LS-DYNA code.•Three material models in the dynamic tensile regime calibrated.•Computed and measured transmitter bar tensile pulses correlated after revisions.

The effort invested in improving our understanding of the physics of high energy explosion events has tremendously increased in the past few decades. Moreover, the dramatic increase in computer capabilities over the last two decades made the numerical simulation approach the dominant tool for investigating blast wave related phenomena and their effects. However, both large- and small-scale field tests are still in use. In the following, we present an experimental tool capable of better resolving and studying the blast–structure interaction phenomenon. In addition, this experimental tool can assist in validating numerical simulations of these phenomena prior to applying them to simulate large-scale events. The experimental tool uses an exploding wire technique to generate small-scale cylindrical and spherical blast waves. This approach permits safe operation, high repeatability, and usage of advanced diagnostic systems that cannot be used in large-scale field experiments. The system was calibrated using an analytical model, an empirical model, and a numerical simulation. To ensure that spherical blast geometry was achieved, a set of free air blast experiments in which high-speed photography was used to monitor the blast wave structure was conducted. Furthermore, by using similitude analysis the results obtained from small-scale experiments can be applied to full-scale problems. It has been clearly shown that an exploding wire system offers an inexpensive, repeatable, safe, easy to operate, and effective experimental tool for studying phenomena involving blast–structure interactions.

The capability to predict the consequences of explosion through computer simulations is of great practical importance. The physical processes involved in a detonation phenomenon, though, are extremely complex. Therefore, the common practice is to resort to empirical or semiempirical equations of state (EOSs) describing the detonation properties of explosives. Becker–Kistiakowski–Wilson (BKW) and Jones–Wilkins–Lee (JWL) are among the most widely used EOS. The purpose of this work is to conduct a comparative study between them. A special emphasis was given to the description of the contaminants dispersion caused by the explosion (in addition to the usual interest in describing blast waves). In particular, we study the implications of these differences within the framework of our current computational methodology using the open source CFD toolbox—OpenFOAM [1].

Small-scale modeling of explosive events has become an important tool in the investigation of blast wave-structure interactions. In this approach, a full-scale model is miniaturized and subjected to “gram-scale” explosions from detonated micro-charges. While offering a cheaper, faster, and ultimately more manageable alternative to full-scale field tests, small-scale testing also offers better reliability and accuracy in more complex scenarios where numerical simulations become limited. Nevertheless, small-scale experiments introduce other difficulties due to the reliance on the well-known Cranz-Hopkinson “cube-root” scaling law. This scaling relationship is suitable for self-similar open-field experiments but does not necessarily apply to urban scenarios. Additionally, chemical explosive charges of such small quantities might be susceptible to changes in parameters such as the explosive compound compression strength, the humidity of the explosive and of the surrounding atmosphere, the method of ignition, etc. Logistically, the handling and preparing of the experimental setup with these small chemical explosives requires specially trained personnel and permits. To overcome these challenges, the exploding wire (EW) technique offers an elegant substitute to using small chemical charges in scaled-down modeling.

Induced heating in a vacuum environment is the most common method for high precision and purity casting. A significant disadvantage in this process is that it is designed for heating in a crucible of uniform diameter. However, it is not suited for the heating of a crucible with stepped diameter. The use of a variable diameter crucible enables to place a larger amount of raw material into the wider diameter section of the crucible. After the material melts, the liquid fills the narrow part of the crucible and enables better control of liquid flow into the casting mold. Hence, in this research we present a novel solution for vacuum inductive heating in a stepped diameter crucible by using a secondary heating coil (SHC). In order to examine the SHC solution, numerical models were developed to describe the temperature distribution and the heat generation in the crucible. Experiments on a vacuum induction furnace were conducted to validate the numerical models of the SHC. A good match was acquired between the numerical and experimental results. The results of the simulations and experiments have shown great improvement in the capability of heating a stepped diameter crucible with an SHC. (C) 2016 Elsevier Ltd. All rights reserved.

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The Concrete Damage Model that is implemented in the LS-Dyna code is capable of simulating the behavior of plain concrete under complex static and dynamic loading conditions. However, the values for the numerous parameters, which are required as an input, are left for the user to provide. In this study the Concrete Damage Model was calibrated for a wide range of strong concretes, using triaxial-compression-test data that were obtained from the literature. In contrast, the adjustment of the parameters of the present model is provided as a function of the unconfined compressive strength of the concrete. Although, not enough validation has been done either in higher pressures or in actual tests, it is evident that the presently calibrated model shows better agreement with published test results than the model currently available in LS-Dyna.

An elastic cantilever beam subjected to weak impact is investigated with focus on its ability to absorb the impact energy. It was found that the location of impact along the beam has a significant influence on the kinetic energy absorbed. It was established in both, using an experimental setup and numerical computations. A reduced degrees of freedom analytical model of this simple continuous system is analyzed in order to explain its quite complicated behavior. The same impact spot, at which the maximum impact energy was absorbed, was predicted by the analytical model. At this location 90% of the kinetic energy is absorbed in the form of elastic beam vibrations. The results of this demonstration may be used for designing an elastic kinetic energy absorbing system.

Dynamic tests of three reinforced concrete samples and six Dynablok samples were performed in the blast simulator facility at the University of California San-Diego (UCSD). The purpose of these tests was to evaluate the performance of a novel protective wall design. These tests were numerically simulated at the Protective Technologies Research and Development Center (PTR&DC) of the Ben-Gurion University (BGU) in Beer-Sheva, Israel. The simulations were carried out using two commercial hydro-codes: LS-Dyna and Dytran. The purpose of these simulations was to calibrate the parameters of the material models available in the above codes. Once calibrated, the simulation results showed good agreement with the test results for largely deflected yet moderately damaged specimens.

The deflection of a clamped thin shell spherical cap is evaluated by the finite element method. Elastic material properties are assumed. The ratio of the center height to the base radius of the cap is used to distinguish shallow from deep caps. Comparing the deflection of clamped shallow caps to deep ones resulted in a very interesting behavior which may contradict the intuition of some engineers. For example, the deflection of a shallow clamped cap is considerably larger than that of a sphere or hemisphere with the same radius of curvature. The causes for this behavior are discussed. Results are presented for a wide range of geometries, pressures, and material properties for design purposes.

The absorbing matrix of a volumetric (directly irradiated) solar receiver must be exposed to the concentrated incoming sunlight. Most applications require that the receiver operates at an elevated pressure and in many cases the working fluid is not air. These requirements can be met only if the receiver is equipped with a transparent window. A novel frustum-like high-pressure (FLHiP) window, made of fused silica, is presented. Optical, mechanical, and thermal analyses, over 1,000 hours of accelerated life-time tests and several hundred hours of tests in a solar receiver, show that this window satisfies the required criteria for operation in a volumetric solar receiver, whose operating pressure and peak absorber temperature reach 30 bar and 1700°C, respectively.

One of the most debated issues concerning the origin of life, is how enzymes which are essential for existence of any living organism, evolved. It is clear that, regardless of the exact mechanism, the process should have been specific and reproducible, involving interactions between different molecules. We propose that substrate templating played a crucial role in maintaining reproducible and specific formation of prebiotic catalysts. This work demonstrates experimentally, for the first time, substrate-directed formation of an oligopeptide that possesses a specific catalytic activity toward the substrate on which it was formed. In our experiments we used the substrate o-nitrophenol-β-d-galactopyranoside (ONPG) as a molecular template for the synthesis of a specific catalyst that is capable of cleaving the same substrate. This was achieved by incubation of the substrate with free amino acids and a condensing agent (dicyandiamide) at elevated temperatures. A linear increase with time of the reaction rate (d[product]/d2t), pointed to an acceleration regime, where the substrate generates the formation of the catalyst. The purified catalyst, produced by a substrate-directed mechanism, was analyzed, and identified as Cys2-Fe+2. The mechanism of substratedirected formation of prebiotic catalysts provides a solution to both the specificity and the reproducibility requirements from any prebiotic system which should evolve into the biological world.

Our understanding of how life emerged on Earth has much to do with speculations about the ways in which prebiotic catalysts could have been formed. Since enzymes, the contemporary biological catalysts, are polymers of amino acids, we looked at the possible activity of free amino acids as catalysts. In this study it is shown experimentally that mixtures of free amino acids exert catalytic activities of β-galactosidase, carbonic anhydrase, and catalase. We also observed different levels of catalytic activty of individual amino acids: some were more efficient than others. Apparently, assemblies of amino acids which were formed around substrate molecules through weak interactions, could, in principle, catalyze many prebiotic reactions. This might have been one step in the emergence of biological enzymes.

Algorithms for solving partial differential equations which extend previous applications of the nonconforming Taylor discretization method (NTDM) are presented. In one modification the number of interrelated grid points is variable, thus enabling additional geometric flexibility. Another modification is the approximation of the governing differential equation using the method of weighted residuals. A simple one-dimensional test case with a known analytic solution is solved using this code. The results demonstrate that precision is enhanced when using the method of weighted residuals with an increased number of interrelated points. The algorithm is applied as a general purpose two-dimensional code for nonlinear steady state heat-conduction. Two-dimensional examples with complex geometry and boundary conditions are then solved both by the NTDM and by the finite elements method (FEM). The results obtained by the two methods are compared.

An algorithm for the numerical solution of field problems is presented. The method is based on expanding the unknown function in a Taylor series about some nodal points so that the coefficients of the series for the various nodes are considered as unknowns. Discrepancy between the values resulting from Taylor expansions about distinct nodes is allowed if it is on the same order of magnitude as the estimated error resulting from the discretization. This enables considerable savings in computation effort in addition to the advantage of specifying the accuracy of the obtained solution. Geometrical flexibility, which enables handling complex boundaries for a large variety of field problems, is another advantage of the proposed scheme. The algorithm is applied to nonlinear steady-state heat-conduction. A test case is treated numerically, and for the evaluation of the scheme the results are compared with the analytical solution.