Tensile Wave Research Articles

Reduction of Bubble Cavitation by Modifying the Diffraction Wave from a Lithotripter Aperture

A new method was devised to suppress the bubble cavitation in the lithotripter focal zone to reduce the propensity of shockwave-induced renal injury. An edge extender was designed and fabricated to fit on the outside of the ellipsoidal reflector of an electrohydraulic lithotripter to disturb the generation of diffraction wave at the aperture, but with little effect on the acoustic field inside the reflector. Although the peak negative pressures at the lithotripter focus using the edge extender at 20 kV were similar to that of the original configuration (-11.1 ± 0.9 vs -10.6 ± 0.7 MPa), the duration of the tensile wave was shortened significantly (3.2 ± 0.54 vs 5.83 ± 0.56 μs, P<0.01). There is no difference, however, in both the amplitude and duration of the compressive shockwaves between these two configurations as well as the -6 dB beam width in the focal plane. The significant suppression effect of bubble cavitation was confirmed by the measured bubble collapse time using passive cavitation detection. At the lithotripter focus, while only about 30 shocks were needed to rupture a blood vessel phantom using the original HM-3 reflector at 20 kV, no damage could be produced after 300 shocks using the edge extender. Meanwhile, the original HM-3 lithotripter at 20 kV can achieve a stone comminution efficiency of 50.4 ± 2.0% on plaster-of-Paris stone phantom after 200 shocks, which is comparable to that of using the edge extender (46.8 ± 4.1%, P=0.005). Modifying the diffraction wave at the lithotripter aperture can suppress the shockwave-induced bubble cavitation with significant reduced damage potential on the vessel phantom but satisfactory stone comminution ability.

A comparison of light spot hydrophone and fiber optic probe hydrophone for lithotripter field characterization

The performance of a newly developed light spot hydrophone (LSHD) in lithotripter field characterization was compared to that of the fiber optic probe hydrophone (FOPH). Pressure waveforms produced by a stable electromagnetic shock wave source were measured by the LSHD and FOPH under identical experimental conditions. In the low energy regime, focus and field acoustic parameters matched well between the two hydrophones. At clinically relevant high energy settings for shock wave lithotripsy, the measured leading compressive pressure waveforms matched closely with each other. However, the LSHD recorded slightly larger |P_| (p < 0.05) and secondary peak compressive pressures (p < 0.01) than the FOPH, leading to about 20% increase in total acoustic pulse energy calculated in a 6 mm radius around the focus (p = 0.06). Tensile pulse durations deviated ~5% (p < 0.01) due to tensile wave shortening from cavitation activity using the LSHD. Intermittent compression spikes and laser light reflection artifacts have been correlated to bubble activity based on simultaneous high-speed imaging analysis. Altogether, both hydrophones are adequate for lithotripter field characterization as specified by the international standard IEC 61846.

Discrete element modeling of rock failure dynamics

The discrete element method is employed to study rapid failure of a test rock specimen under cylindrical tensile wave effect. The author proves the effect exerted by the mechanical characteristics of rocks and the boundary conditions of the problem on the length and shape of fractures, and compares the experimental evidence with the calculation data.

Dynamic tensile strength of polyurea

Abstract

Deformation behavior and spalling fracture of a heterophase aluminum alloy with ultrafine-grained and coarse-grained structure subjected to a nanosecond relativistic high-current electron beam

The results of a comprehensive experimental–theoretical investigation of the deformation behavior, regular features and mechanism of spalling fracture in an Al–Mg–Li–Zr heterophase aluminum alloy with ultrafineand coarse-grained structure subjected to a nanosecond high-current electron beam with the power density 7·109 W/cm2 are presented. The patterns of formation and propagation of a shock wave are discussed, and so is the behavior of the respective reflected wave, once the former is reflected from the back surface. Common regularities of variation in the thickness of the spalled layer and its plastic deformation degree are observed in the cases of ultrafine- and coarse-grained structure. It is shown that spalling resistance of the Al–Mg–Li–Zr heterophase alloy is controlled by the ultrafine-grained structure formed in the spalling zone under the tensile wave rather than by the initial grain structure.

Debonding strength of bundled glass fibers subjected to stress pulse loading

This paper reports experimental results of the debonding propagation of bundled-fibers specimens subjected to a tensile stress wave. In addition, the paper also presents a dynamic debonding model for the problem on the basis of the cohesive zone model, and verifies the model by comparing the predicted debonding to the experimental data. The established numerical model is used to study the propagation mode of the debonding, and the result suggests that in this particular specimen design and loading condition, the debonding initiated in a mixed mode condition. However, the mode II quickly increased and dominated the mode I during an early debonding propagation up to certain extend where the mode mixity became constant.

Phase-field modeling of fracture in liquid

Phase-field theory for the description of the overdriven fracture in liquid (cavitation) in tensile pressure wave is developed. Various results from solid mechanics are transferred into mechanics of fluids. Thermodynamic potential is formulated that describes the desired tensile pressure–volumetric strain curve and for which the infinitesimal damage produces infinitesimal change in the equilibrium bulk modulus. It is shown that the gradient of the order parameter should not be included in the energy, in contrast to all known phase-field approaches for any material instability. Analytical analysis of the equations is performed. Problems relevant to the melt-dispersion mechanism of the reaction of nanoparticles on cavitation in spherical and ellipsoidal nanoparticles with different aspect ratios, after compressive pressure at its surface sharply dropped, are solved using finite element method. Some nontrivial features (lack of fracture at dynamic pressure much larger than the liquid strength and lack of loc...

Blast Resistance of Double-Layered Reinforced Concrete Slabs Composed of Precast Thin Plates

When designing blast-resistant reinforced concrete (RC) structures, reducing spall damage due to reflected tensile stress waves is a major problem. Furthermore, for rapid construction of the blast-resistant structures against sudden terrorist bomb attacks, it is necessary to build it with precast concrete walls and reduce the weight of the precast elements by reducing their size for ease of transportation and construction.In this study, to propose an idea for rapid construction and better blast resistance of blast-resistant RC structures, double-layered RC slabs composed of precast thin plates, 50 mm thick, were fabricated and utilized for contact detonation tests. The tests were conducted under a condition that the amount of explosives and the dimensions of specimen were constant respectively, and two types of concrete, normal concrete and polyethylene fiber reinforced concrete (PEFRC), were employed as the slab materials. Our results showed that creating an air cavity between the two layers of PEFRC slab was effective in reducing spall damage, while the air space had no advantage in normal RC, under a condition that the thickness of the air space was fixed at 15 mm. Furthermore, the above difference between PEFRC and normal RC slabs was discussed, based on the numerical result on the fracture process of the air-sandwiched normal RC slab.

Blast Resistance of Polyethylene Fiber Reinforced Concrete to Contact Detonation

When designing blast-resistant reinforced concrete (RC) structures, reducing spall damage due to reflected tensile stress waves is a major problem. To investigate the applicability of polyethylene fiber reinforced concrete (PEFRC) for use in blast-resistant RC structures, experimental investigations were conducted to evaluate the damage to PEFRC slabs subjected to contact detonation. As a result, it was shown that PEFRC was effective in reducing the spall damage due to contact detonation as compared with normal RC. Moreover, an equation for estimating damage depth to the PEFRC slab subjected to contact detonation was derived based on the test results.

Adhesive bond strength evaluation in composite materials by laser-generated high amplitude ultrasound

Adhesive bonding of composites laminates is highly efficient but is not used for joining primary aircraft structures, since there is presently no nondestructive inspection technique to ensure the quality of the bond. We are developing a technique based on the propagation of high amplitude ultrasonic waves to evaluate the adhesive bond strength. Large amplitude compression waves are generated by a short pulse powerful laser under water confinement and are converted after reflection by the assembly back surface into tensile waves. The resulting tensile stresses can cause a delamination inside the laminates or at the bond interfaces. The adhesion strength is evaluated by increasing the laser pulse energy until disbond. A good bond is unaffected by a certain level of stress whereas a weaker one is damaged. The method is shown completely non invasive throughout the whole composite assembly. The sample back surface velocity is measured by an optical interferometer and used to estimate stress history inside the sample. The depth and size of the disbonds are revealed by a post-test inspection by the well established laser-ultrasonic technique. Experimental results show that the proposed method is able to differentiate weak bond from strong bonds and to estimate quantitatively their bond strength.

Atomic Scale Studies of Spall Behavior in Single Crystal Cu

The micromechanisms related to ductile failure during dynamic loading of single crystal Cu are investigated using large-scale molecular dynamics (MD) simulations. Void nucleation, growth, and coalescence is studied for a single-crystal Cu system under conditions of impact of a shock piston with a velocity of 500 m/s. The compressive shock wave generated reflects from the rear surface as a tensile wave and meets with the tail of the shock wave at the spall plane. The interaction results in a triaxial tensile stress state that nucleates a large number of voids at the spall plane. MD simulations suggest that voids nucleate at intersections of stacking faults generated in the spall plane under the triaxial tensile stress conditions. Two stages of void growth are observed during dynamic failure of single-crystal Cu: Stage I corresponds to fast nucleation and growth of the nucleated voids and Stage II corresponds to coalescence and slow growth of the voids.

Energy Dissipation in Explosive Welding of Dissimilar Metals

Explosive welding of two dissimilar metallic sheets is accomplished by the exhaustive deformation owing to high pressure and high temperature created at the collision place. This study addresses the analytical estimation of the dissipation of potential energy of the explosive initially to mechanical energy and then to thermal energy in dissimilar Copper – Low carbon steel combination. The emanating pressure in the region of detonation front is transmitted to flyer surface as compressive stress wave and a reflective tensile wave is generated at the bottom surface of the flyer. A dilational wave and shear wave are generated. As the flyer plate moving with the transmitted wave collides with the parent, the available kinetic energy is converted into thermal energy to produce adequate heat to induce plastic deformation thus resulting into a strong metallurgical bond.

Adhesive bond testing of carbon–epoxy composites by laser shockwave

Adhesive bonding, particularly of composite laminates, presents many practical advantages when compared with other joining methods but its use is limited, since there is presently no non-destructive inspection technique to ensure the quality of the bond. We are developing a technique based on the propagation of high amplitude ultrasonic waves to evaluate the adhesive bond strength at high strain rate. Compression waves are generated by a short and powerful laser pulse under water confinement and are converted after reflection on the assembly back surface into tensile waves. The resulting tensile forces normal to the interfaces can cause a delamination inside the laminates or a disbond. The adhesion strength is probed by increasing the laser pulse energy until disbond. A good bond is unaffected by a certain level of stress whereas a weaker one is damaged. The method is shown completely non-invasive throughout the whole composite assembly. The sample back surface velocity is measured by an optical interferometer and used to estimate stress history inside the sample. The depth and size of the disbonds are revealed by a post-test inspection by the well established laser-ultrasonic technique. Experimental results confirmed by numerical simulations show that the proposed method is able to differentiate weak bonds from strong bonds and to estimate quantitatively the bond strength.

Impact-induced tensile waves in a kind of phase transforming materials

This paper concerns the global propagation of impact-induced tensile waves in a kind of phase-transforming materials. It is well-known that the governing system of partial differential equations is hyperbolic-elliptic and the initial-boundary value problem is not well-posed at all levels of loading. By making use of fully nonlinear stress-strain curve to model this material, Dai and Kong succeeded in constructing a physical solution of the above initial-boundary value problem. For the impact of intermediate range, they assumed that $\beta<3\alpha$ in the stress-response function for simplicity. In this paper, we revisit the impact problem and consider the propagation of impact-induced tensile waves for all values of the parameters $\alpha$ and $\beta$. The physical solutions for all levels of loading are obtained completely.

Pressure-time profiles of a focused and a radial shockwave device: Measurements in tissue, ex vivo, and in a water bath.

In the past we have employed shock waves (SW) to stimulate periosteal cell proliferation in both rat and rabbit models. In order to understand the mechanical insult to the cells, single pulse pressure-time profiles were recorded at a periosteal surface using a needle hydrophone for both a ballistic and an electrohydraulic SW source. Three sets of measurements were taken: free field (FF) in a water bath, intramuscularly (IM) by inserting the needle into the leg of a sacrificed rabbit and placing it near the tibial bone corner, and ex vivo using an extracted rabbit tibia bone in a water bath and placing the needle closer to the bone surface. For the ballistic source, the IM and FF measurements of the leading positive peak matched, whereas for the electrohydraulic source, it was attenuated by 57%. The compression was followed by a tensile wave, and for both sources, IM and FF measurements of the pressure and duration were similar. The ex vivo measurements showed additional secondary peaks for the measurements at the bone surface, attributable to surface reflections or creeping waves. These data suggest that periosteal cells subject to SWs are exposed to complex pressure fields that likely stimulate the cell proliferation.

On the response of rubbers at high strain rates—II. Shock waves

In this series of papers, we examine the propagation of waves of finite deformation in rubbers through experiments and analysis; in the present paper, Part II, attention is focused on the propagation of one-dimensional tensile shock waves in strips of latex and nitrile rubber. Tensile wave propagation experiments were conducted at high strain rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in rubber strips. Shock waves have been generated under tensile impact in prestretched rubber strips; analysis of the response yields the tensile shock adiabat for rubbers. The propagation of shocks is analyzed by developing an analogy with the theory of detonation; it is shown that the condition for shock propagation can be determined using the Chapman–Jouguet shock condition.

On the response of rubbers at high strain rates—I. Simple waves

In this series of papers, we examine the propagation of waves of finite deformation in rubbers through experiments and analysis; in the present paper, Part I, attention is focused on the propagation of one-dimensional waves in strips of natural, latex and synthetic, nitrile rubber. Tensile wave propagation experiments were conducted at high strain rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in rubber strips. Analysis of the response through the theory of finite waves indicated a need for an appropriate constitutive model for rubber; by quantitative matching between the experimental observations and analytical predictions, an appropriate instantaneous elastic response for the rubbers was obtained. This matching process suggested that a simple power-law constitutive model was capable of representing the high strain-rate response for both rubbers used.

Laser shock-induced spalling and fragmentation in vanadium

Polycrystalline and monocrystalline (〈1 0 0〉 and 〈1 1 0〉) vanadium was subjected to shock compression followed by tensile wave release to study spall and fragmentation behavior. The shock pulse was generated by a direct laser drive at energy levels ranging from 11 to 440 J mm –2 (laser beam irradiated area 1.12 mm 2) and initial pulse durations of 3 and 8 ns (approximate initial pressures between 10 and 250 GPa). Glass and polycarbonate shields placed at a specific distance behind the vanadium targets were used to collect and analyze the ejected fragments in order to evaluate and quantify the extent of damage. The effects of target thickness, laser energy, polycrystallinity and pulse duration were studied. Calculations show melting at a pressure threshold of ∼150 GPa, which corresponds to a laser energy level of ∼180 J mm –2. Consistent with the analytical predictions, the recovered specimens and fragments show evidence of melting at the higher energy levels. Spalling in the polycrystals occurred by a ductile tearing mechanism that favored grain boundaries. In the monocrystals it occurred by a mixture of cleavage fracture along the {0 1 0} planes and ductile dimple fracture. This lower spall strength in polycrystals contradicts predictions from the Hall–Petch equation. Experimentally obtained fragment sizes were compared with predictions from the Grady–Kipp model. The spall strength of vanadium under laser loading conditions was calculated from both VISAR pull-back signals and using the spall thickness. It was found to be considerably higher than predictions from gas gun experiments, the monocrystals showing a higher value than polycrystals. This higher spall strength is suggestive of a strong time dependence of the phenomenon, consistent with the nucleation and growth kinetics of voids and the strain rate sensitivity embedded in the Grady theory.

Measurement of spall strength of A12024-T4 and SS304 in plate impact experiments

Spall (dynamic fracture) strength of A12024-T4 and SS304 alloy have been determined at high strain rate. Gas gun experiments have been conducted on A12024-T4 and SS304 target plates in symmetric impact configuration. The spall in A12024-T4 and SS304 plates has been achieved by impacting them with parallel flying plates accelerated to velocities of 0.56 km/s and 0.6 km/s, respectively. The plate impacts in the two experiments introduced a shock wave of 4.38 GPa and 11.9 GPa, respectively in A12024 and SS304 target plates. In each experiment the interaction of tensile waves resulting from the reflection of shock wave from the target free surface and from the flyer free surface generated large tensile stress in the target which exceeded the spall strength causing spall fracture. The analysis of the velocity history of the target free surface recorded using VISAR reveals the dynamic yield strength of A12024-T4 to be 0.355 and spall strength of 1.46 GPa at strain rate of ~ 104 /s. These quantities in SS304 were determined to be 0.8 GPa and 2.69 GPa with strain rate of ~ 104 /s.

Relationship between spall characteristics and the dimension of fractal fracture structures

The effect of the fractality of a fracture surface and spall contour on the characteristics [fracture time (strength) and spall strength] of the loaded material is studied. It is shown that an increase in the fractal dimensions of the spall contour leads to an increase in the material strength parameter in the tensile wave and spall strength, whereas an increase in the fractal dimension of the fracture surface leads to a decrease in the spall strength. As an example, the spall strength is calculated taking into account the fractality of the fracture surface for Sp. 28 steel.