The impact of flat, thin plates on aluminum targets in the 5–10 km/s velocity range

The purpose of the study was to investigate the effect of the impact of a thin membrane on aluminum in the velocity range 6–10 km/s. The impulsive load delivered by a membrane impact will exceed the momentum/area of the membrane because of rebound, blow-off of vaporized membrane material, and ejection of molten and fractured material from the target (impulse gain). One of the objectives of the study was to quantify the impulse gain in the velocity range of interest. Also of interest was the physical damage to the target including spall, melting and fracture. Understanding these damage mechanisms is important for protecting spacecraft from the impact of space debris and meteoroids.

Simple theories account for the flyer rebound, but hydrodynamic modeling is required to treat the blow-off of target material. At lower velocities, the blow-off is negligible, but at10 km/s calculations show it to be equal to the rebound momentum for one-dimensional (1-D) impacts. The modeling of three-dimensional (3-D) experiments revealed large effects at the edge of an impacting membrane, prompting an emphasis on 1-D pressure profile experiments.     

Deformed microstructure evolution in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s

Deformed microstructure in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s⁻¹ were investigated through optical microscope, scanning electron microscope and transmission electron microscope. The results show that four deformed zones around the crater can be classified based on the different deformed microstructure, including ultrafine grain zone, ultrafine grain and deformation twin zone, high and low density deformation twin zones. The dislocation slipping, deformation twins and ultrafine grains are the dominant components in the four deformed zones, and the evolution of deformed microstructure is speculated based on the deformed microstructure observed in four zones. Slipping and twinning play a critical role for the formation of the dynamic recrystallized grains, and twinning-induced rotational dynamic recrystallization mechanism is thought to be the main mechanism for the formation of ultrafine grains. The microhardness and dynamic compressive strength in different deformed zones were measured, and the high microhardness and yield strength in ultrafine grain zone should be attributed to the strain hardening and grain refining.     

Fracture strength testing of δ-alumina fibres with variable diameters and lengths

Tensile tests were performed on individual δ-alumina fibres (Saffil, RF grade). The results revealed a large scatter in strengths and a clear dependence of the fracture strength on the specimen volume. The tests were evaluated on the basis of the Weibull probability function, a special modification of the Weibull analysis being developed that successfully copes with the problem of testing fibres with various diameters and test lengths. For the sample studied the Weibull modulus, m, was found to be 2·2, with a scaling constant δ₀ = 6·0 MPa (units of volume mm³; i.e. V₀ = 1 mm³).     

Simulation and analysis of the capacitance–voltage characteristics of the δ-doped semiconductors

In this paper, a self-consistent model to simulate the general characteristics of one-dimensional semiconductor structures is demonstrated. During calculation, possible quantum effects and the distributions of both electrons and holes are all considered. In this model, a continuity equation is solved to calculate the distribution of free electrons and holes. The possible quantum wells are sought using the Schrödinger equation. The overall charge density and potential are obtained self-consistently by an iteration scheme. The C–V characteristics of the δ-doped structures are simulated and then compared with those of practical samples. By comparing with these δ-doped samples, the effective numbers of dopant atoms can be precisely determined. For these highly doped samples, it is found that the activation rates are only about half. This finding can be verified by Hall measurements which confirms the accuracy in this study.     

Fatigue crack initiation in Hastelloy X – the role of boundaries

In polycrystalline metals, microstructural features such as grain boundaries (GBs) influence fatigue crack initiation. Stress and strain heterogeneities, which arise in the vicinity of GBs, can promote the nucleation of fatigue cracks. Because of variations in grain size and GB types, and consequently variations in the local deformation response, scatter in fatigue life is expected. A deeper quantitative understanding of the early stages of fatigue crack nucleation and the scatter in life requires experimental and modelling work at appropriate length scales. In this work, experiments are conducted on Hastelloy X under fatigue conditions, and observations of fatigue damage are reported in conjunction with measurements of local strains using digital image correlation. We use a recent novel fatigue model based on persistent slip band–GB interaction to investigate the scatter in fatigue lives and shed light into the critical types of GBs that nucleate cracks. Experimental tools and methodologies, utilizing ex situ digital image correlation and electron backscatter diffraction, for high resolution deformation measurements at the grain level are also discussed in this paper and related to the simulations.     

Crystal structure of the orthorhombic U2-Al4Mg4Si4 precipitate in the Al–Mg–Si alloy system and its relation to the β′ and β″ phases

The atomic structure of a common precipitate in the Al–Mg–Si system has been determined. It is isotypic with TiNiSi (space group Pnma) and contains four units of MgAlSi in a unit cell of size a = 0.675 nm, b = 0.405 nm, c = 0.794 nm. EDS analyses support the composition. A model was based on the atomic structure of the β′ precipitate, electron diffraction and high-resolution transmission electron microscopy (HRTEM) images. A quantum mechanical refinement of the model removed discrepancies between simulated and experimental diffraction intensities. Finally, a multi-slice least square refinement confirmed the structure. The structural relation with β″ is investigated. A similar Mg–Si plane also existing in β″ and β′, can explain most coherency relations between the precipitate phases and with matrix.     

Effects of trace zirconium on the initiation and propagation behavior of fatigue cracks in Cu–6Ni–2Mn–2Sn–2Al alloy

The effects of trace Zr on the fatigue behavior of Cu–6Ni–2Mn–2Sn–2Al alloy were studied through the initiation and growth behavior of a major crack. When stress amplitude was less than σ_a = 350 MPa, the fatigue life of Zr-containing alloys was about 2 times larger than that of alloy without Zr. When σ_a = 400 MPa, the effects of Zr addition on fatigue life disappeared. Increased fatigue life due to Zr addition resulted from an increase in crack initiation life and microcrack growth life. Zr addition generated strengthened grain boundaries (GBs) that developed from the precipitation of SnZr compounds. Strengthened GBs contributed to the increase in crack initiation life. The effects of Zr addition on fatigue behavior were discussed with relation to the behavior of microcracks.     

EURAXLES – A global approach for design,production and maintenance of railway axles: WP4 – “Tools,technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the free axle surface“

Work Package 4 “Tools, technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the axle surface” of the EURAXLES project aimed on development of practical solutions for wheelset protection systems to avoid corrosion and damages at the axles and thus minimizing the risk of axle failures. The work included investigations for improving the paint adhesion by grit‐blasting of the axle surface, alternative and innovative coating systems, recommendations for quality tests of painting and coatings and also investigation of unpainted axles.     

Generation and analysis of FCG data using a single specimen and Kmax–ΔK testing matrix

A custom method to generate fatigue crack growth (FCG) data requires testing of multiple specimens at different load ratios, R, and the application of a load shedding procedure from pre-cracking level to threshold. In this paper, a novel method of testing has been investigated which utilizing a single specimen and a testing matrix in terms of K_max and ΔK values corresponding to predetermined R-ratios for which FCG data are recorded. Automatic K-controlled tests on 2324-T39 Al alloy were conducted using both increasing and decreasing ΔK procedures while K_max was kept constant. Results show that the increasing ΔK procedure gives less scatter than decreasing ΔK procedure. Also, fatigue crack growth curves near the threshold region obtained from increasing ΔK are above the curves obtained from decreasing ΔK procedure. These differences are explained by means of interaction between cyclic plastic zones and their effect on fatigue damage. The procedure with increasing ΔK demonstrated minimal interaction effects and hence it is recommended for efficient FCG data generation. The proposed procedure reduces testing time, the overall scatter associated with multiple samples and eliminates possible uncertainty linked to the load shedding procedure and its effects on threshold.     

Combined Microwave and Laser Heating for Glazing of 8Y–ZrO2 and 8Y–ZrO2/ZrSiO4–Composites

Sintered porous yttria‐stabilized zirconia and zirconia composite ceramics with zirconium silicate are surface glazed by Laser‐Assisted Microwave Plasma Processing (LAMPP). Suitable process parameters for surface glazing are determined for those ceramics. The plasma process is monitored by means of pyrometry and optical emission spectroscopy. In order to prove the quality of the surface glazing and to characterize hot corrosion resistance, tests with molten vanadium pentoxide are performed. After 4 h of exposure, the penetration depth of the molten salt is investigated as a function of ceramic composition and pre‐treatment by glazing. Upon hot corrosion testing of glazed and non‐glazed ceramics, the molten vanadium pentoxide reacts selectively with yttrium oxide, forming yttrium vanadate, and causes crack formation in the zirconia ceramics due to transition to monoclinic zirconia. The results for LAMPP‐glazed ceramics show, that a surficial melting phase is achieved because process temperatures exceed 3000 °C. Hence, a dense, crack‐free and hardness‐enhanced surface layer achieves a better resistance to hot corrosion as compared to non‐glazed ceramics. Due to LAMPP‐glazing, the vanadium ingress is reduced from 33 to 7 μm for yttria‐stabilized zirconia and from 104 to 17 μm for zirconia composite ceramic. Reactions and microstructural changes taking place upon LAMP‐Processing are discussed.

     

Structural and optical properties of (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) glasses and glass nanocrystal composites

Glasses of various compositions in the system (100 − x)(Li₂B₄O₇) − x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (10  x  60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li₂B₄O₇ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (E_opt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m^*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied.     

The two‐shearfield test – A suitable method for the empirical shear capacity design of masonry / Der Zweifeld‐Schubversuch – Eine praxistaugliche Methode zur versuchsgestützten Bemessung der Schubtragfähigkeit von Bestandsmauerwerk

The investigations [1] demonstrate that the two‐shearfield test is a suitable method for the determination of the shear capacity of masonry. The testing equipment is mounted directly on the wall in order to retain realistic boundary conditions like stiffness, load and prior damage. The behaviour factor q and the capacity curves of certain masonry walls can be directly obtained from the experimental results and realistic material behaviour in earthquake design can be represented. In particular, existing masonry can be assessed realistically with methods like the response spectrum, the push‐over and the capacity spectrum by using the two‐shearfield test.     

Temperature dependencies of excited states lifetimes and relaxation rates of 3–5 phonon (4–6 μm) transitions in the YAG, LuAG and YLF crystals doped with trivalent holmium, thulium, and erbium

The temperature dependencies of the nanosecond multiphonon relaxation (MR) rates of the ³F₃ state of Tm³⁺ in the YLF crystal and of the ⁵F₅ state of Ho³⁺ ion in the YAG and LuAG crystals and of the microsecond MR rates of the ⁴F_9/2 (²H_9/2) state of Er³⁺ ions in YLF were measured in the wide temperature range using direct laser excitation and selective fluorescence kinetics decay registration. For YLF the observed relations are explained by 4-phonon process in the frame of a single-frequency model with hω_eff=450±30 cm⁻¹ for the ³F₃ state of Tm³⁺ and by 5-phonon process with hω_eff=445 cm⁻¹ for the ⁴F_9/2 (²H_9/2) state of Er³⁺. For YAG and LuAG crystals these dependencies are explained by the 3-phonon process with hω_eff=630 cm⁻¹. The decrease of the relaxation rate with the temperature in the range from 13 to 80 K was observed for the ⁴F_9/2 (²H_9/2) state of Er³⁺ in the YLF crystal. It is explained by the redistribution of excited electronic states population of erbium ions over the higher lying Stark levels with different MR probabilities. A good fit of experimental temperature dependence (including the dropping part of the experimental curve) was obtained for single-frequency model (hω_eff=450 cm⁻¹) with W₀₁=8.0×10⁴ s⁻¹ and W₀₂=4.7×10⁴ s⁻¹ accounting Boltzmann distribution of population over two excited Stark levels of the excited state of erbium ions. Employment of this model improves the fit between the experiment and the theory for the ⁵F₅ state of Ho³⁺ ion in YAG as well. Strong influence of the parameters of the non-linear theory of MR, i.e. the reduced matrix elements U^(k) of electronic transitions and the phonon factor of crystal matrix η on the spontaneous MR rates was observed experimentally. The smaller these parameters the slower the spontaneous MR W₀. This fact can be used for searching new active crystal laser media for the mid-IR generation.     

The influence of confinement on the penetration of ceramic targets by KE projectiles at 1.8 and 2.6 km/s

This paper presents the results of scale size experiments using a tungsten-alloy long-rod projectile fired against 97.5% Al₂O₃ ceramic targets at 1.8 and 2.6 km/s. Two targets were used, one having lateral steel confinement; the other without. The projectile overmatched the target, and residual projectile length and velocity were recorded using ballistic-syncro photography. Flash radiography was used during penetration of the unconfined target to obtain the penetration velocity. Manganin pressure gauges were also used to obtain additional data on the response of the ceramic target during penetration. Results from the eight experiments indicate that the confinement reduced the residual energy of the projectile at both impact velocities. Expressed in terms of the projectile impact energy, 55–56% was lost in the unconfined target at 2.6 km/s compared with 60% for the confined design. The same trend was found at 1.8 km/s with 68% and 72–73% for the unconfined and confined, respectively. Predictions using the QinetiQ GRIM2D hydrocode and a simplified form of the Johnson–Holmquist ceramic material model agreed well with the experiments for three out of the four test configurations. The predicted projectile erosion and retardation against the confined target at 1.8 km/s was excessively high. Analytical predictions using the Tate modified Bernoulli equation also gave reasonably accurate predictions for three of the tests, but values for the Tate target ‘strength’ extracted from experiments using a different target configuration were not accurate for the target design used in this paper.     

Current developments in fire protection – Changeover to design and classification according to the Eurocode / Aktuelle Entwicklungen im Brandschutz – Umstellung auf die Bemessung und Klassifizierung nach europäischen Normen

The European requirements for fire safety design and testing of structural masonry members are already the governing requirements in many cases. In principle, both the European and the German classification may be used according to the Bauregelliste. However, the latter may only be used when European classification of a member or construction material is not possible because the appropriate European standards do not exist. The European standards do not differ fundamentally from the German standard DIN 4102‐2. One significant difference is that according to the DIN 4102‐2, it was required to carry out two tests with the most unfavourable result governing, while according to the European standard, only one test is required. According to the EN Standard, the tests for fire resistance and the reaction to fire are carried out separately. There are other differences related to the pressure in the furnace as well as the use of plate thermocouples instead of jacketed thermocouples. Fire safety design of masonry is carried out in accordance with EC 6‐1‐2 and the National Annex. Only the members not regulated in the EC 6‐1‐2, e.g. pre‐cast masonry members, non‐load‐bearing walls, lintels, connections and joints, should be designed and checked according to the revised DIN 4102‐4.     

Sol–gel preparation of boron-containing cordierite Mg2(Al4−xBx)Si5O18 and its crystallization

Five cordierite-based powders were investigated regarding their thermal and crystallization behaviors. The powders were obtained from amorphous gels having nominal compositions of 2Mg : xAl : (4 − x)B : 5Si where x = 4 down to 0. Thermal gravimetry analysis of the dry gels showed some absorbed water and decomposition of organic ligands in addition to network condensation. Gradual substitution of B for Al in the dried gel powders showed a new band in their infrared spectra corresponding to triangular BO₃, whereas the bands corresponding to Al vanished. This also showed a noticeable effect on the crystallization trends, type and stability of cordierite. Cordierite crystallized in samples of B/Al ratio up to 1 while protoenstatite predominated in samples of higher B/Al ratios. In addition, some silica minerals, with little amorphous phase, were formed. Incorporation of boron and increase in temperature enhanced the transformation of γ cordierite to its form.     

“Segment-wise model” for theoretical simulation of barely visible indentation damage in composite sandwich beams: Part II – Experimental verification and discussion

When localized transverse loading is applied to a sandwich structure, the facesheet locally deflects and the core crushes. A residual dent induced by the core crushing significantly degrades the mechanical properties of the sandwich structure. In a previous paper, the authors established a “segment-wise model” for theoretical simulation of barely visible indentation damage in honeycomb sandwich beams with composite facesheets. Honeycomb sandwich beam was divided into many segments based on the periodic shape of the honeycomb and complicated through-thickness characteristics of the core were integrated into each segment. In this paper, the new model is validated by experiments using specimens with different types of honeycomb cores. In addition, the damage growth mechanism under indentation load was clarified from the viewpoint of the reaction force from the core to the facesheet. The applicability of the model to other types of core materials is also discussed.     

ZW-47/30型氧压机活塞杆燃烧事故的分析及处理

介绍了ZW-47/30型氧压机在运行过程中出现三级活塞杆燃烧事故的经过及损坏情况,分析了事故原因,提出了避免氧压机燃烧等重大事故发生的有效措施。     

Verification of sound insulation in residential building – the new DIN 4109 / Nachweis des Schallschutzes im Wohnungsbau – die neue DIN 4109

The central sound insulation standard for building in Germany, DIN 4109, was issued in a revised version in July 2016. The calculation procedures described in the standard can now be used to verify constructional sound insulation for masonry buildings with insulated external walls. For other building materials and construction methods, the minimum requirements can be verified, or if required the enhanced requirements. Measurements in completed buildings confirm the results and show that provided the construction materials are suitable and the specialist design is correct, good sound protection is regularly achieved.