Applied Mechanics and Materials Vol. 782

Abstract: In this paper experimental research on rotating detonation carried out at the Institute of Aviation (IA) in Warsaw are presented. Research was focused on 3-D numerical simulations of detonation propagation in cylindrical chambers and on evaluation of conditions at which rotating detonation is propagating in cylindrical channels for kerosene-hydrogen-air mixtures. Conducted simulations are used for analysis of complex flow – detonation front interaction and for estimating the thermodynamic parameters of the outflow gases. Extensive research on continuously propagating rotating detonation in many different chambers and in different fuel-air mixtures were tested. On bases of conducted calculations, as well as results of experimental study, a few chamber were selected for tests with GTD-350 engine. It was shown that application of the continuously rotating detonation to GTD-350 engine can results with increased efficiency of the engine.

Abstract: Efficiently and accurately predicting structural dynamic response and damage to external blast loading is a big challenge to both structural engineers and researchers. Theoretical investigation on this problem is complex as it involves non-linear inelastic material properties, effect of time varying strain rates, uncertainties of blast load calculations and the time-dependent structural deformations. Experimental investigation can provide valuable data for locating the damage and establishing the damage criteria. The damage curves generated from the extensive experimental study can provide quick assessment of the structural status. However, such blast experiments always involve safety concern and can be beyond the affordability. Besides this, the correlation of the experimental data with predictive method is difficult since it requires a large number of tests to generate damage curves. Compared with the theoretical and experimental study, numerical simulation does not involve any safety concern and is cost-effective. With verified material model and element model, numerical simulation could be powerful supplement to the experimental tests. However, numerical simulation of structural responses under blast and impact loading could be time and resource consuming. Even with modern computer technology and computational mechanics method, detailed modelling and numerical simulation of responses of structures subjected to blast loadings are still often prohibitive. To address this issue, in the present study, an efficient numerical method is proposed to reliably calculate structural response and damage to blast loadings.

Abstract: In order to use a low flammability magnesium alloy as structural components, very high cycle fatigue properties of this alloy (AMCa602) were investigated. S-N properties obtained in both rotating bending and axial loading were compared with each other. It was found that S-N curve in the axial loading appeared a little lower than that in the rotating bending due to the differences of stress distributions and critical volumes for both loading types. Moreover, the statistical aspect on the fatigue property was analyzed as P-S-N characteristics in the rotating bending. After fatigue tests, fracture surfaces of failed specimens were observed by means of a scanning electron microscope (SEM) and the microstructures at the crack initiation site and the propagation path were also observed by combining FIB technique and EBSD analysis. Thus, it was found that some specimens failed from surface inclusions and their fatigue lives were lower in comparison to those of the specimens without surface inclusions. In addition, the fracture surfaces of this alloy revealed very rough in the usual life region, whereas a characteristic smooth area was observed on the fracture surfaces of specimens failed in the surface inclusion-initiated fracture and in very high cycle regime. A stress intensity factor range at the front of the smooth area (ΔK_smooth) tended to a definite value so that the fracture mechanism of this alloy was governed by a concept of ΔK.

Abstract: Basic physical problems of jet formation process on the basis of Lavrentiev-Birkhoff classical scheme are analyzed. It is shown that in process of realization of hypercumulation conditions for jet formation without complete stagnation point involving formation of the inner zone of constant pressure (dead zone), the flow mass is always greater than slug mass, that is unachievable in the known models. Smoothing effect of this zone on the development of different types disturbances, particularly, smoothing Rayleigh-Taylor instability for thin liner may be expected and shown in simulations.

Abstract: In this paper, the dynamic deformation and rupture of pre-notched thin metal plates subjected to confined blast loading were investigated. The thin copper plates with cross-shape pre-notch were clamped on the end of a confined cylinder vessel by a cover flange. An explosive charge with a mass of 4g was detonated in the vessel center to generate blast load acting on the metal plates. The images of metal plates were recorded by two high-speed cameras. The displacement and strain fields during the deformation and rupture process were measured by using 3D digital image correlation (3D DIC). The effects of pre-notches on the dynamic deformation and rupture of thin metal plates were analyzed. The microstructure of fracture surface was examined The 3D DIC technique is proven to be an effective method to conduct dynamic full-field deformation measurement.

Abstract: The high temperature deformation and fracture behavior of ultra-high strength G33 steel under high strain rate compression are investigated by means of a split Hopkinson p ressure bar. Impact tests are performed at strain rates of 1000/s and 2200/s and at temperatures ranging from 25°C to 700°C. The SEM and TEM techniques are also used to analyze the microstructure evolution of the adiabatic shear band (ASB) and fracture characteristics of the deformed specimens at high temperature. The experimental results indicate that the flow stress of G33 steel is significantly dependent on temperatures and strain rates. The flow stress of G33 steel increases with the increase of strain rates, but decreases with the increase of temperatures. The strain rate sensitivity is more pronounced at the low temperature of 25°C. In addition, G33 steel is more liable to fracture at high temperatures than at 25°C. Observations of microstructure show two well-developed symmetric parabolic adiabatic shear bands on the longitudinal cross-section of the cylindrical specimen deformed at the temperature of 700°C and at the strain rate of 2200/s. Within the ASB, the width of the fine equiaxed grain structure is about 7μm. The size of those equiaxed grains is approximately 100nm. The fracture analysis results indicate that the ASBs are the predominant deformation and the specimens fracture along adiabatic shear bands. The fracture surfaces of the deformed G33 steel specimens are characterized by two alternating zones: rough dimple zone and relatively smooth shear zone. Further observations reveal that smooth shear zones consist of severely sheared dimples.

Abstract: As a new material, the microstructure of β20C titanium alloy can match well with property by forging process. However, the microstructure of billet is inhomogeneous in actual forging. For ensuring microstructures homogenization, two forging processes are designed. Process 1 is large deformation above the phase transition (T=1050°C, 70% deformation) and small deformation in two-phase region (T=860°C~890°C, ≤40% deformation). Process 2 is small deformation above the phase transition (T=1050°C, 40% deformation) and large deformation in two-phase region (T=860°C~890°C, 50%~60% deformation). Then microstructures are observed and dynamic compressive strength and the critical fracture strain of samples are test after solid-solution treatment. It turns out that the homogeneity of microstructure of process 2 is improved by heat treatment. The microstructure is lamellar microstructure with 1650MPa dynamic strength and 15% critical fracture strain through “Process 1 + 840°C 1h/FC” while the microstructure is equiaxed microstructure with 1650MPa dynamic strength and 20% critical fracture strain through “Process 2 + 840°C 1h/FC”. In conclusion, the microstructure of large deformation in two-phase region can accumulate more deformation energy which is beneficial for dynamic recrystallization.

Abstract: Electroless copper plating method combined with spark plasma sintering (SPS) was used to fabricate W-Cu alloy with low W-W contiguity. Results show that W-Cu alloy with low W-W contiguity and high relative density can be obtained by this method. With sintering temperature increased from 860°C to 1060°C, the relative density of W-Cu alloy shows a rapidly increasing tendency, but the W-W contiguity keeps at a low level. Compression testing results show that the ductility of prepared W-Cu alloy is sensitive to strain rate, and the failure strain of the W-Cu alloy shows obviously increasing tendency with the loading strain rate increased from 10^-3 to 10³.

Abstract: Bioplastics are plastics derived from renewable sources such as corn starch or microbe and biodegradable plastics are plastics that are capable of being decomposed by bacteria or other living organisms. Poly (lactic acid) (PLA) is a typical and biodegradable bioplastic. It has been recognized as a promising alternative material for petroleum-based polymers. In order to increase Young’s modulus, in the present study, silica nanoparticles were added to PLA. The effects of the addition of silica nanoparticles and the surface treatment of nanosilica particles on dynamic properties of nanoparticle added PLA were examined using tensile split Hopkinson pressure bar method and the Izod impact strength tests.