Laboratory X-ray diffraction complex for studying structural changes in materials under shock loading

A diagnostic laboratory X-ray diffraction complex has been designed to study the crystal structure under shock loading. Electric explosion of a foil, which accelerates a plane dielectric impactor, is used to generate a plane shock wave. A plasma-focus gas discharge chamber acts as an X-ray source. An automated system for recording X-ray diffraction patterns of shock compressed crystals has been developed on the basis of an image intensifier and a digital CCD camera. Recorded patterns of shock compressed LiF single-crystal structures are presented, which demonstrate that nonequilibrium structural formations have been obtained.     

A laser ultrasonic technique for studying the properties of products manufactured by additive technologies

Study of the possibility for using a laser ultrasonic technique in nondestructive testing of products that are manufactured by selective laser melting is presented. Procedures of producing samples and carrying out nondestructive testing by the laser ultrasonic technique are described. Mechanical properties of samples that were grown in vertical and horizontal directions have been measured, as well as the speed of ultrasound in these samples. It has been established that the laser-ultrasonic technique is a promising technology for the quality control of products that are obtained by selective laser melting.     

A streak-photography method for measuring the shock-wave velocity in experiments on studying the equation of state of matter on the Iskra-5 laser facility

A technique for measuring the velocity of a shock wave arising in laser-irradiated samples in experiments involved in studies of the shock compressibility of substances is described. This method ensures a spatial resolution of 10 μm, an error in measuring the shock-wave delay in layers of 10 ps, an error in measuring the shock-wave velocity of 2.5%, and a dynamic range of recording of ∼200. The measurement results are presented. Original Russian Text ? S.A. Bel’kov, A.G. Kravchenko, A.V. Kunin, D.N. Litvin, V.M. Murugov, A.V. Senik, 2006, published in Pribory i Tekhnika Eksperimenta, 2006, No. 2, pp. 150–153.     

Sheet metal formability analysis for anisotropic materials under non-proportional loading

Sheet metal formability is conventionally assessed in a two-dimensional plot of principal strains or stresses in comparison to a forming limit curve. This method of assessment implicitly assumes that the forming limit is isotropic in the plane of the sheet. While the assumption of isotropy in the forming limit is perhaps a good engineering approximation, it is intrinsically inconsistent with the use of material models that are anisotropic. Since the trend today is to utilize models with full anisotropy in order to more accurately capture the physics of material behavior, the issue of anisotropy of forming limits must also be addressed. The challenge is that the forming limit is no longer defined by a curve but requires the definition of a surface in strain or stress space, and therefore it is no longer appropriate to view these limits with the convenience of two-dimensional diagrams. Furthermore, recent developments in the characterization of sheet forming limits under non-proportional loading suggest that is advantageous to view forming limit behavior in terms of stresses rather than strains, a view that is adopted in this paper. A solution to the challenge of assessing formability for an anisotropic material is proposed that rescales the stresses by a factor so that the scaled stresses have the same relationship to a single forming limit curve in a 2D plot in stress-space, as the actual stresses have to the true anisotropic forming limit in 3D space. The rescaling enables engineers to accurately view the formability of all the elements at the same time for a given finite element analysis of an application. This paper also discusses other challenges of using stresses in the assessment of formability, focusing on an analysis of the 2-Stage Forming Benchmark highlighted in the Numisheet ’99 Conference. Stresses are found in this application to unload to non-critical values after reaching critical levels earlier in a forming process, which suggests that a full integration of the stress-based forming limit criterion with FE simulation is required to detect critical states that may temporarily occur during the forming process.     

用于激光驱动冲击波诊断的成像型VISAR设计

利用激光驱动冲击波是高压状态方程研究的主要手段之一,一般利用扫描光学高温计(SOP)对冲击波进行诊断,但SOP存在的靶场干扰、无法实现弱冲击波测量和状态方程绝对测量等缺陷。为解决这些问题,提出了一种用于激光驱动冲击波诊断的双灵敏度成像型任意反射面速度干涉仪(VISAR)设计,并给出了VISAR各组成部分的技术要求。     

Fatigue wear of materials under dynamic contact loading

Regularities of the fatigue fracture of surface layers of metals, as well as polymer and inorganic materials, under friction are discussed. The kinetics of the growth of fatigue microcracks and mechanisms of the formation of wear particles under various loading conditions are described. It is shown that, at the initial stage, the volume fatigue fracture of friction members that experience dynamic loading results from their fatigue wear.     

A technique for studying the spectral composition and duration of radiation accompanying a shock wave at the rear surface of materials under direct laser irradiation

A photochronographic technique for studying the spectral composition and duration of radiation that accompanies the appearance of a shock wave on the rear surface of a loaded target has been developed. The spectral resolution of this technique was evaluated. A method of the through calibration of the recording channel using radiation of a source with the known spectrum was proposed. The results of the performed calibration are used to restore the spectral distribution on the basis of the obtained spectrochronograms.     

Fracture behaviour of adhesively-bonded composite materials under impact loading

In this paper, a polymeric unidirectional carbon-fibre epoxy-resin composite is both experimentally and numerically investigated to study the nonlinear material behavior of impacted DCB (Double Cantilever Beam) specimens. For the impact analysis, the load and the displacement applied from pin onto end block as well as the crack energy release rate are measured and compared with the finite element analysis results. The energy release rate is a critical measure of the resistance to crack propagation, which can be estimated by the force and displacement at the crack tip. It is found that the energy release rate measured from impact tests on the specimens is well predicted by the suggested finite element model in this study.     

Forming severity concept for predicting sheet necking under complex loading histories

A new method of predicting neck formation in sheets under non-proportional loading is proposed, based on the concept of “cumulative forming severity”. This concept is borrowed from a macroscopic model of ductile fracture where the crack initiation is governed by the accumulated equivalent plastic strain modified by the stress triaxiality and the Lode angle parameter. Such an approach necessitates a representation of the forming limit diagram (FLD) in the space of the equivalent strain to neck and the Lode angle parameter.Another new factor is the assumption of the non-linear accumulation of forming severity for non-proportional and complex loading histories. A class of non-linear weighting function is proposed with only one free parameter. A starting point in the derivation is the known FLD corresponding to proportional loading. This can be determined from Hill's and Stören and Rice analytical solutions, from numerical simulation, or else taken directly from experiments. In the case of proportional loading, necking depends on the final state of stress or strain, so it does not matter if necking severity index is accumulated in a linear or non-linear way. For non-proportional loading, the unknown free parameter of the non-linear accumulation rule must be determined from a test.Experimental data on FLDs under complex strain paths for two types of material, aluminum alloy 6111-T4 [Graf A, Hosford W. The influence of strain-path changes on forming limit diagrams of A1 6111 T4. International Journal of Mechanical Sciences 1994;36(10):897–910.] and aluminum-killed sheet steel [Muschenborn W, Sonne HM. Influence of the strain path on the forming limits of sheet metal. Archiv fur das Eisenhuttenwesen 1975;46:597–602], found in the literature are revisited by the proposed model. Calibrated from only one test with non-proportional loading condition, the model is able to predict the remaining tests of complex loading paths with good accuracy.     

An interferometer with time-and-frequency signal compression for studying properties of materials in shock wave experiments

A two-channel infrared (1.55 μm) laser interferometer intended for measuring velocities of free surfaces in shock-wave experiments is described. Characteristics of the device and comparison results with the VISAR interferometer are given. A combination of Photonic Doppler Velocimetry (PDV) and PDV-Pivot interferometric schemes allows one to implement operation in four different modes and efficiently use capabilities of up-to-date digital oscilloscopes. A 4-GHz bandwidth oscilloscope enables one to measure velocities in a range of 0–6 km/s. The proposed interferometer is efficient for studies of the properties of structural materials, inner ballistics, detonation kinetics, and projectile ability of explosives.     

Recording channel of a coordinate X-ray detector for studying the density dynamics of objects under pulsed loading

This paper describes the structure, operation algorithm, and circuitry of the recording channel of a multi-channel coordinate X-ray detector with a microsecond time resolution for studying the dynamics of density distribution in objects under pulsed loading. A method for fast automatic real-time control of the channel sensitivity is proposed.     

A mobile complex for on-line studying water areas and surface atmosphere

The complex is intended to perform continuous measurements of concentrations of chlorophyll a and dissolved organic substances by the laser induced fluorescence method, evaluate a state of the photosynthetic system of phytoplankton cells, and record readings of the CO₂ gas analyzer, sensors of sea water saltiness, pH, and temperature, and solar illumination meter. The mobility of the complex ensures a possibility of its operation on different ships and under stationary conditions. The configuration of the complex can be promptly changed for solving the current problem by promptly adding or replacing separate devices and sensors of the complex, as well as the software integrating all devices and data into the system. It is possible to use standard, vibration-resistant laboratory equipment, since the housing of the designed device ensures protection against the marine environment. Results of in-situ measurements performed in the Peter the Great Gulf (Sea of Japan) in 2012 are given.     

激光辐照下尼龙纤维材料的热烧蚀规律

为了得到激光辐照下尼龙材料的烧蚀规律,利用红外成像的方法分析了近红外连续激光辐照尼龙材料引起的热烧蚀现象。用摄像机和红外热像仪记录了尼龙材料在烧蚀过程中的主要现象和温度变化过程,并对实验结果与ANSYS仿真结果进行了对比。使用波长为976nm,输出功率密度为1×105 W/m2、光斑高斯半径为10mm的光束对尼龙材料进行照射的结果显示:开始时尼龙材料温度迅速上升,发生膨胀,并逐渐熔融分解;随着照射时间的增加,尼龙材料温度变化变缓,熔融部分向光斑边缘退化;当达到一定温度时,材料温度不再升高。由于受光束质量、材料性能不均匀、熔融部分向边缘退化等因素影响,得到的实验烧蚀结果与理论烧蚀结果稍有差异,但基本吻合,验证了实验方法及ANSYS数值仿真方案的可行性。     

Acoustic-emission testing of the strength of metal structures under complex loading

Russian Journal of Nondestructive Testing - The interpretation of the results of acoustic-emission (AE) testing of the states of objects under complex loading, which possess a branched structure...     

A plant for studying radiation and thermal desorption of gases from inorganic materials

A high-vacuum plant and methods for studying thermal and radiation-stimulated desorption from solid-state materials are described. Radiation-stimulated desorption was studied using an electron gun with a 1- to 120-keV beam energy, featuring a new technology of power supply units. Partial pressure gages with a sensitivity of up to 10⁻¹³ Pa were used to record mass spectra of residual gases. Results of studying thermal- and radiation-stimulated yields of hydrogen from submicrocrystalline samples of a BT-6 alloy are presented to demonstrate the serviceability of the created procedures.     

A device for studying the scattering properties of fluid droplet samples

Scattering indicatrices can yield substantial information on the composition and properties of samples in studies of dispersive media by optical methods. This paper describes a simple and convenient experimental setup that allows measurements of the scattering indicatrices (at angles from −90° to +90°) of fluid samples in the form of sessile droplets with concurrent recording and estimation of the geometrical parameters of the lateral projection of a droplet sample. The results of studying samples of blood with different levels of hematocrit and different types of erythrocyte aggregation are presented. The device can be used both in scientific research for studying physical properties of liquids and in clinical diagnostic practice for staging a number of existing hematological, immunological, and biochemical tests.     

A radio-frequency impedance spectroscope for studying interaction of high-power laser radiation with crystals

A radio-frequency impedance spectroscope for studying the interaction of high-power laser radiation with nonlinear optical crystals has been developed. It has been revealed that the shape of the piezoelectric resonance line of a crystal heated with laser radiation is identical under both uniform heating in the absence of laser radiation and nonuniform heating resulting from the action of laser radiation. This allows introduction of the notion of the equivalent crystal temperature characterizing the nonuniform temperature distribution in a crystal exposed to laser radiation.     

Springback analysis of thin rectangular bars of non-linear work-hardening materials under torsional loading

A theoretical analysis of the springback of narrow rectangular strips of non-linear work-hardening material under torsional loading has been carried out. This theoretical analysis is supported by experimental results for rectangular mild steel strips of different thicknesses and lengths. Finally an analytical generalized expression relating angle of twist to twisting moment and residual angle of twist per unit length for rectangular strips under plastic torsion is obtained in non-dimensionalized form. A comparison between the results obtained for bars of non- linear and linear work-hardening materials loaded under torsion is also made.     

An experimental study on the behaviour under impact loading of metallic cellular materials

This paper presents an experimental study on the impact response of metallic cellular materials, i.e. aluminium honeycombs of various cell sizes and wall thicknesses, aluminium foams made from two different manufacturing processes (IFAM and Cymat), as well as hollow sphere agglomerates (nickel and iron). A 60 mm diameter nylon Hopkinson pressure bar is used to improve the signal/noise ratio and to host larger samples containing a sufficient number of cells. Quasi-static and classical Split Hopkinson Pressure Bar (SHPB) tests as well as direct impact Hopkinson bar tests (higher speeds up to 50 m/s) are performed. Significant rate sensitivities are observed for most of the cellular materials studied. Analyses of the potential causes of this macroscopic rate sensitivity show that the microinertia effect in the successive folding process could be an important factor.