2008 Vol. 28, No. 3
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2008, 28(3): 193-199.
doi: 10.11883/1001-1455(2008)03-0193-07
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Abstract:
The Hopkinson pressure bar tests were performed to explore the spall characteristics of concrete materials by analyzing the strain waves of the buffer bar. The experimental results, for concretes with different spall strengths at different load rates, indicate that the spall strength of concrete is related with its compressive strength and load rate. An empirical formula was proposed to describe the functional relationship between spall strength, compressive strength and load rate. The rate effect of spall strength mainly results from the different expending paths of crack in concrete at different load rates. Some special efforts, which include the effect of the load compressive wave damage on concrete spall fracture, the results of reduplicate load experiments and the sequences of the multiple spall process, explain that damage plays an important role in the spall fracture of concrete.
The Hopkinson pressure bar tests were performed to explore the spall characteristics of concrete materials by analyzing the strain waves of the buffer bar. The experimental results, for concretes with different spall strengths at different load rates, indicate that the spall strength of concrete is related with its compressive strength and load rate. An empirical formula was proposed to describe the functional relationship between spall strength, compressive strength and load rate. The rate effect of spall strength mainly results from the different expending paths of crack in concrete at different load rates. Some special efforts, which include the effect of the load compressive wave damage on concrete spall fracture, the results of reduplicate load experiments and the sequences of the multiple spall process, explain that damage plays an important role in the spall fracture of concrete.
2008, 28(3): 200-206.
doi: 10.11883/1001-1455(2008)03-0200-07
Abstract:
The MTS810 and SHPB were used to experimentally study the quasi-static and dynamic mechanical properties of Kevlar/epoxy composite laminates. Effects of the strain rate and lay-up types of fiber on the mechanical behaviors of laminated Kevlar were discussed. Based on the strain-rate curves of laminated Kevlar, an empirical constitutive equation was proposed in which the strain-rate hardening and damage softening effects of the material were taken into consideration. A stiffness-strengthened factor was introduced into the proposed constitutive equation to describe the influences of fiber lay-up types on the mechanical properties of the laminates. Results show that the introduced factor is reasonable in the fitted and experimental stress-stain curves.
The MTS810 and SHPB were used to experimentally study the quasi-static and dynamic mechanical properties of Kevlar/epoxy composite laminates. Effects of the strain rate and lay-up types of fiber on the mechanical behaviors of laminated Kevlar were discussed. Based on the strain-rate curves of laminated Kevlar, an empirical constitutive equation was proposed in which the strain-rate hardening and damage softening effects of the material were taken into consideration. A stiffness-strengthened factor was introduced into the proposed constitutive equation to describe the influences of fiber lay-up types on the mechanical properties of the laminates. Results show that the introduced factor is reasonable in the fitted and experimental stress-stain curves.
2008, 28(3): 207-302.
doi: 10.11883/1001-1455(2008)03-0207-06
Abstract:
A new type tandem shaped charge warhead, which produces a high-velocity jet and low-velocity jetting projectiles, was proposed based on the characteristics of a reinforce concrete target. The formation processes of the prepositioned charge and rear-mounted charge were simulated by the three-dimensional finite element dynamic code LS-DYNA3D. Series static armor-piercing tests were carried out to validate the performance of the proposed tandem shaped charge and in the experiment it penetrated a reinforce concrete target and a 45 steel target. Experimental results reveal that the proposed tandem shaped charge can do more damage to reinforce concrete target and drill a larger hole in it than the conventional tandem shaped charge. Experimental and simulated researches show that the new tandem shaped charge has promising applications to the tandem shaped charge warheads against hard objects such as reinforce concrete targets, airdrome runways, multi-plate spaced targets.
A new type tandem shaped charge warhead, which produces a high-velocity jet and low-velocity jetting projectiles, was proposed based on the characteristics of a reinforce concrete target. The formation processes of the prepositioned charge and rear-mounted charge were simulated by the three-dimensional finite element dynamic code LS-DYNA3D. Series static armor-piercing tests were carried out to validate the performance of the proposed tandem shaped charge and in the experiment it penetrated a reinforce concrete target and a 45 steel target. Experimental results reveal that the proposed tandem shaped charge can do more damage to reinforce concrete target and drill a larger hole in it than the conventional tandem shaped charge. Experimental and simulated researches show that the new tandem shaped charge has promising applications to the tandem shaped charge warheads against hard objects such as reinforce concrete targets, airdrome runways, multi-plate spaced targets.
2008, 28(3): 213-219.
doi: 10.11883/1001-1455(2008)03-0213-07
Abstract:
An experimental model, in which explosive strips were placed along the welds on single side or on double sides, was developed to simulate the circumferential weld of a large pressure-resistant cylindrical shell according to its welding craft and to explore how to relieve the circumferentially welded residual stresses. In the model experiments the two arrangements of explosive strips were both adopted to relieve the circumferentially welded residual stresses of a large pressure-resistant cylindrical shell using explosive treatment. Experimental results indicate as follows: (1) there are high welded residual stresses in the circumferential weld of the large pressure-resistant cylindrical shell; (2) single and double side treatments are both effective to regulate and relieve welded residual stresses; (3) the higher the welded residual stress, the better the relieving effect; (4) when the residual stress is higher than 0.5s, the single side treatment can relieve the residual stress m more than 40%, the double side treatment can relieve it more than 60%; (5) longitudinal stress can be relieved effectively by placing explosive strips along the weld.
An experimental model, in which explosive strips were placed along the welds on single side or on double sides, was developed to simulate the circumferential weld of a large pressure-resistant cylindrical shell according to its welding craft and to explore how to relieve the circumferentially welded residual stresses. In the model experiments the two arrangements of explosive strips were both adopted to relieve the circumferentially welded residual stresses of a large pressure-resistant cylindrical shell using explosive treatment. Experimental results indicate as follows: (1) there are high welded residual stresses in the circumferential weld of the large pressure-resistant cylindrical shell; (2) single and double side treatments are both effective to regulate and relieve welded residual stresses; (3) the higher the welded residual stress, the better the relieving effect; (4) when the residual stress is higher than 0.5s, the single side treatment can relieve the residual stress m more than 40%, the double side treatment can relieve it more than 60%; (5) longitudinal stress can be relieved effectively by placing explosive strips along the weld.
2008, 28(3): 220-224.
doi: 10.11883/1001-1455(2008)03-0220-05
Abstract:
Preheated explosive consolidation (PHEC) experiments were performed on the -Al2O3 nanometer ceramic powders under different explosive pressures at the preheated temperature of about 0.5Tm. The crystal types for the studied ceramic powders were analyzed by using the X-ray diffraction data, and their microstructures were observed with a high-resolution scanning electronic microscope. The experimental results show as followings: (1)when the shock pressure reaches 13.1 GPa, the -Al2O3 nanometer powders are well sintered to -Al2O3 crystal type; (2)the crystal grains in the sintered bulk are combined tightly with each other and the average grain size is around 100 nm, but the -Al2O3nanometer powders cannot be changed into -Al2O3 crystal type when the shock pressure decreases to 9.35 GPa.
Preheated explosive consolidation (PHEC) experiments were performed on the -Al2O3 nanometer ceramic powders under different explosive pressures at the preheated temperature of about 0.5Tm. The crystal types for the studied ceramic powders were analyzed by using the X-ray diffraction data, and their microstructures were observed with a high-resolution scanning electronic microscope. The experimental results show as followings: (1)when the shock pressure reaches 13.1 GPa, the -Al2O3 nanometer powders are well sintered to -Al2O3 crystal type; (2)the crystal grains in the sintered bulk are combined tightly with each other and the average grain size is around 100 nm, but the -Al2O3nanometer powders cannot be changed into -Al2O3 crystal type when the shock pressure decreases to 9.35 GPa.
2008, 28(3): 225-228.
doi: 10.11883/1001-1455(2008)03-0225-04
Abstract:
An improved evaluation method is discussed, which can be used to optimize the blasting plans by using the fuzzy analytic hierarchy process (FAHP) with the real coding-based accelerating genetic algorithm (RAGA). Fuzzy preferential relation matrixes are established with the blasting plans and the evaluation indexes. The values of the weights and the optimum values meeting the minimizing condition of consistency index coefficient (CIC) are calculated by means of RAGA, and the best blasting plan is selected according to the general optimum value of each plan. The practical example shows that the proposed method can be used to gain the rational weights, and its accuracy, dispersion, and operability are better than those of the traditional FAHP.
An improved evaluation method is discussed, which can be used to optimize the blasting plans by using the fuzzy analytic hierarchy process (FAHP) with the real coding-based accelerating genetic algorithm (RAGA). Fuzzy preferential relation matrixes are established with the blasting plans and the evaluation indexes. The values of the weights and the optimum values meeting the minimizing condition of consistency index coefficient (CIC) are calculated by means of RAGA, and the best blasting plan is selected according to the general optimum value of each plan. The practical example shows that the proposed method can be used to gain the rational weights, and its accuracy, dispersion, and operability are better than those of the traditional FAHP.
2008, 28(3): 229-225.
doi: 10.11883/1001-1455(2008)03-0229-07
Abstract:
A parallel computation program for reactive flow was developed based on two-dimensional unstructured grid by adopting the modified CE/SE (space-time conservation element and solution element) method and parallel domain decomposition technology. The computational domain was decomposed into several sub-domains and the parallel computation was conducted by introducing the multi-tube PDE (pulsed detonation engine) with convergent-divergent nozzle. The processes of ignition in single tube and propagation in multi-tube were simulated for H2 and O2 under stoichiometric ratio conditions by using the 8-species, 34-elementary reaction model. Computed results demonstrate the followings: (1) the CE/SE method can capture the complicated detonation flow structures, and the conclusion in this paper agrees well with that in the literature; (2) detonation waves generated in single tube have significant influences on flow field structures of side-tubes and can ignite the fresh reactant in them.
A parallel computation program for reactive flow was developed based on two-dimensional unstructured grid by adopting the modified CE/SE (space-time conservation element and solution element) method and parallel domain decomposition technology. The computational domain was decomposed into several sub-domains and the parallel computation was conducted by introducing the multi-tube PDE (pulsed detonation engine) with convergent-divergent nozzle. The processes of ignition in single tube and propagation in multi-tube were simulated for H2 and O2 under stoichiometric ratio conditions by using the 8-species, 34-elementary reaction model. Computed results demonstrate the followings: (1) the CE/SE method can capture the complicated detonation flow structures, and the conclusion in this paper agrees well with that in the literature; (2) detonation waves generated in single tube have significant influences on flow field structures of side-tubes and can ignite the fresh reactant in them.
2008, 28(3): 236-242.
doi: 10.11883/1001-1455(2008)03-0236-07
Abstract:
The 3D finite element analysis model for multi-layered spaced beam-edge structure under bird impact is established by taking the typical fuselage support structure of a certain type airplane as the object. Numerical results of the crucial parts during bird impact are obtained by using the ALE-Lagrange coupling method in the non-linear program (ANSYS/LS-DYNA), and the critical velocity when the beam-edge structure fails is achieved. The effects on structure response of different impact locations are investigated, and the structure failure mechanism for bird impact is analyzed. Both the structure deformation and failure mode from the simulation are consistent with the results of the prototype test, which proves the validity of the method and model proposed in this paper.
The 3D finite element analysis model for multi-layered spaced beam-edge structure under bird impact is established by taking the typical fuselage support structure of a certain type airplane as the object. Numerical results of the crucial parts during bird impact are obtained by using the ALE-Lagrange coupling method in the non-linear program (ANSYS/LS-DYNA), and the critical velocity when the beam-edge structure fails is achieved. The effects on structure response of different impact locations are investigated, and the structure failure mechanism for bird impact is analyzed. Both the structure deformation and failure mode from the simulation are consistent with the results of the prototype test, which proves the validity of the method and model proposed in this paper.
2008, 28(3): 243-251.
doi: 10.11883/1001-1455(2008)03-0243-09
Abstract:
The dynamic response of an elastic-plastic cantilever beam subjected to step loading at its tip was studied numerically by employing large deflection governing equations and solving them expressed in the finite-difference form. The deformation mechanism and energy dissipation were explored by analyzing the instantaneous distribution of internal force, deformation and energy during the early dynamic response and were compared with those of rigid-plastic analysis. Numerical calculation indicates that the deformation mechanism is different due to the magnitude of the step loading. Elastic-plastic analysis confirms the validity of the rigid-plastic theory in dealing with the case of moderate load, and it points out the defects of the rigid-plastic method in the case of low and intense dynamic loads. Comparison with the results calculated by the small deformation theory shows that it is required to consider the large deformation effects.
The dynamic response of an elastic-plastic cantilever beam subjected to step loading at its tip was studied numerically by employing large deflection governing equations and solving them expressed in the finite-difference form. The deformation mechanism and energy dissipation were explored by analyzing the instantaneous distribution of internal force, deformation and energy during the early dynamic response and were compared with those of rigid-plastic analysis. Numerical calculation indicates that the deformation mechanism is different due to the magnitude of the step loading. Elastic-plastic analysis confirms the validity of the rigid-plastic theory in dealing with the case of moderate load, and it points out the defects of the rigid-plastic method in the case of low and intense dynamic loads. Comparison with the results calculated by the small deformation theory shows that it is required to consider the large deformation effects.
2008, 28(3): 252-260.
doi: 10.11883/1001-1455(2008)03-0252-09
Abstract:
A series of normal and oblique penetration experiments were performed to explore the dynamic response of slender projectiles penetrating into typically hard targets. In the experiments, the parameters of the ogive-nose steel projectiles are as follows: the diameter is 14 mm; the lengths are 168, 112 mm; the dimensionless wall thicknesses of the cartridges are 0.1, 0.15; the head factors are 3.0, 4.5. The projectiles were made from 30CrMnSiNi2A and were launched by a light gas gun with 57 mm diameter impact velocities of 100~250 m/s. The processes of impact and projectile deformation were photographed at up to 2104 s-1 using a photron fastcam. The recorded information indicates the following five different structural failure modes for a slender hollow projectile penetrating a typically hard target: (1) local bulges near the dangerous sections on normal impact; (2) plastic buckling on the especial sections without local bulges on normal impact; (3) plastic bending along the deformed region on oblique impact; (4) local plastic bulges coupled and local plastic buckling coupled with generally plastic bending on oblique impact. The penetration modes were established based on the cavity expansion theory. And the control equations were given, which can be used to calculate the yield function in a rigid-perfect plastic free-free beam section subjected to dynamic lateral loading and axial loading. The calculated results are in good agreement with the experiment.
A series of normal and oblique penetration experiments were performed to explore the dynamic response of slender projectiles penetrating into typically hard targets. In the experiments, the parameters of the ogive-nose steel projectiles are as follows: the diameter is 14 mm; the lengths are 168, 112 mm; the dimensionless wall thicknesses of the cartridges are 0.1, 0.15; the head factors are 3.0, 4.5. The projectiles were made from 30CrMnSiNi2A and were launched by a light gas gun with 57 mm diameter impact velocities of 100~250 m/s. The processes of impact and projectile deformation were photographed at up to 2104 s-1 using a photron fastcam. The recorded information indicates the following five different structural failure modes for a slender hollow projectile penetrating a typically hard target: (1) local bulges near the dangerous sections on normal impact; (2) plastic buckling on the especial sections without local bulges on normal impact; (3) plastic bending along the deformed region on oblique impact; (4) local plastic bulges coupled and local plastic buckling coupled with generally plastic bending on oblique impact. The penetration modes were established based on the cavity expansion theory. And the control equations were given, which can be used to calculate the yield function in a rigid-perfect plastic free-free beam section subjected to dynamic lateral loading and axial loading. The calculated results are in good agreement with the experiment.
2008, 28(3): 261-264.
doi: 10.11883/1001-1455(2008)03-0261-04
Abstract:
A one-dimensional, magnetohydrodynamic model, in which the Ohmic heating is considered, was proposed to numerically calculate the experiment Z-452 carried out on the Z machine at Sandia National Laboratories. The computed free-surface velocities of the flyer plates agree well with the experimental records by VISAR. The paper also analyzes the ablation induced by the Ohmic heating in the flyer plates and the penetration of magnetic field. The obtained velocity, pressure history curves are helpful to understand the physical mechanism of magnetically accelerated plane flyers.
A one-dimensional, magnetohydrodynamic model, in which the Ohmic heating is considered, was proposed to numerically calculate the experiment Z-452 carried out on the Z machine at Sandia National Laboratories. The computed free-surface velocities of the flyer plates agree well with the experimental records by VISAR. The paper also analyzes the ablation induced by the Ohmic heating in the flyer plates and the penetration of magnetic field. The obtained velocity, pressure history curves are helpful to understand the physical mechanism of magnetically accelerated plane flyers.
2008, 28(3): 265-270.
doi: 10.11883/1001-1455(2008)03-0265-06
Abstract:
Aiming at the existing problem in blasting vibration velocity calculation, a calculation method by two steps is proposed, in which the shock pressure induced by explosion is first calculated in blasting near region, then the particle vibration velocity farther is calculated. The damping problem in dynamics calculation is discussed preliminarily. The vibration velocities of the different particles under the three different charge conditions with different intervals such as rock powder, water and air, are respectively calculated by means of the proposed method. The calculated ground vertical vibration velocity under the rock powder interval charge condition is maximum, that under the water interval charge condition is inferior and that under the air interval charge condition is minimum. Calculated results accord with the experimental results.
Aiming at the existing problem in blasting vibration velocity calculation, a calculation method by two steps is proposed, in which the shock pressure induced by explosion is first calculated in blasting near region, then the particle vibration velocity farther is calculated. The damping problem in dynamics calculation is discussed preliminarily. The vibration velocities of the different particles under the three different charge conditions with different intervals such as rock powder, water and air, are respectively calculated by means of the proposed method. The calculated ground vertical vibration velocity under the rock powder interval charge condition is maximum, that under the water interval charge condition is inferior and that under the air interval charge condition is minimum. Calculated results accord with the experimental results.
2008, 28(3): 271-275.
doi: 10.11883/1001-1455(2008)03-0271-05
Abstract:
The finite element numerical method is used to study dynamic buckling of cylindrical shells under elastic compression waves. The finite element characteristic equations are derived on the basis of the adjacent-equilibrium criterion and the stress wave theory. In these equations, the compression wave propagation and the transverse inertia effect are taken into consideration. By introducing the dynamic buckling supplementary restraint conditions at the compression wave front of cylindrical shells at the instant when the buckling occurs, the critical-load and dynamic buckling modes of the shells are calculated from the solutions of the finite element characteristic equations. Calculated results provide some insight into the buckling mechanism as a transient process and the influences of the axial stress waves on the buckling deformation.
The finite element numerical method is used to study dynamic buckling of cylindrical shells under elastic compression waves. The finite element characteristic equations are derived on the basis of the adjacent-equilibrium criterion and the stress wave theory. In these equations, the compression wave propagation and the transverse inertia effect are taken into consideration. By introducing the dynamic buckling supplementary restraint conditions at the compression wave front of cylindrical shells at the instant when the buckling occurs, the critical-load and dynamic buckling modes of the shells are calculated from the solutions of the finite element characteristic equations. Calculated results provide some insight into the buckling mechanism as a transient process and the influences of the axial stress waves on the buckling deformation.
2008, 28(3): 276-282.
doi: 10.11883/1001-1455(2008)03-0276-07
Abstract:
Water-entry impact and slamming phenomena fall into complicated transient physical problems whether in theoretical analysis or in numerical simulation. Developments of theory, experiment and numerical simulation on water-entry impact problems were summarized by dividing the concerned researches into three stages in terms of time sequence. The studied content and focus at present on water-entry impact and slamming phenomena were introduced, and numerical modeling techniques were highlighted particularly. Researched results can provide a reference for the further investigation on water-entry impact problems in manned and unmanned spaceflight and marine domains.
Water-entry impact and slamming phenomena fall into complicated transient physical problems whether in theoretical analysis or in numerical simulation. Developments of theory, experiment and numerical simulation on water-entry impact problems were summarized by dividing the concerned researches into three stages in terms of time sequence. The studied content and focus at present on water-entry impact and slamming phenomena were introduced, and numerical modeling techniques were highlighted particularly. Researched results can provide a reference for the further investigation on water-entry impact problems in manned and unmanned spaceflight and marine domains.
2008, 28(3): 283-288.
doi: 10.11883/1001-1455(2008)03-0283-06
Abstract:
The study aimed to explore the gateway design plan for civil defense structure of a typical garage closed up by bonded steel plates. According to this design plan, an experimental model for the steel plate-to-concrete bonded joint structure was proposed to perform an on-site test in an imitated nuclear blast pressure container. The displacement-time curves and the strain-time curves along the vertical supporting steel plates were obtained, which are in agreement with the numerical results by the finite element method. And the bond stresses on the interfaces between the steel plates and the concrete were achieved from the strain distributions along the vertical supporting steel plates. The study examined the supporting reliability of the contact surface between the concrete wall and the steel plate, analyzed the bond-stress distribution along the vertical supporting steel plate subjected to the grade-5 civil defense blast shock wave. The researched results provide a reference to calculate bond stresses between concrete walls and steel plates.
The study aimed to explore the gateway design plan for civil defense structure of a typical garage closed up by bonded steel plates. According to this design plan, an experimental model for the steel plate-to-concrete bonded joint structure was proposed to perform an on-site test in an imitated nuclear blast pressure container. The displacement-time curves and the strain-time curves along the vertical supporting steel plates were obtained, which are in agreement with the numerical results by the finite element method. And the bond stresses on the interfaces between the steel plates and the concrete were achieved from the strain distributions along the vertical supporting steel plates. The study examined the supporting reliability of the contact surface between the concrete wall and the steel plate, analyzed the bond-stress distribution along the vertical supporting steel plate subjected to the grade-5 civil defense blast shock wave. The researched results provide a reference to calculate bond stresses between concrete walls and steel plates.
