摘要:

This paper presents a technique that can be used in order to improve the tensile stresses generated at a substrate-coating interface when the laser spallation adhesion test is performed using a laser source of relatively low power. A theoretical approach based on a construction in the space-time diagram coupled to a representation in the pressure-particle velocity plane (P,u) shows that by impacting a layer of a low impedance material (LIM) stuck on the substrate on its bare face, we are able to improve the peak pressure transmitted to the interface and then the maximum intensity of the tensile stresses. An optimization of the thickness of this LIM layer has been performed to be used with a 1 GW-20ns laser source used in confined irradiation configuration. Experiments conducted on two different substrate-coating systems evidence the efficiency of a low impedance layer in increasing the tensile stresses at the interface. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303679

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We report on a pulsed power experiment performed at the Los Alamos National Laboratory Pegasus facility which was designed to measure material flow at metal interfaces driven to high relative velocities. Material motion at and near four flat Ta/Al(6061) interfaces was measured using flash radiographic techniques. A series of fine Pb wires (407 micron diameter) was implanted in the Al normal to the interfaces. The motion of these markers under shock loading provided a picture of material motion in the Al interfacial region. The surface roughness of the interfaces was varied between 32 and 125 micro-inches. We discuss the implications of these measurements for constitutive models of high speed friction and interfacial morphological change. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303680

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The physical interactions at the contact interface between two metals moving relative to one another are not well understood, particularly when the relative velocity between the bodies becomes a significant fraction of the sound speed in either material. Our goal is to characterize the interfacial dynamics occurring between two metal surfaces sliding at high loads (up to 300 kbar) and at high speeds (greater than 100 m/s). We are developing a technique where a high-speed spinning projectile is fired from a rifled gun at a rod instrumented with electrical resistance strain gauges for measuring both longitudinal and torsional strain waves. The observed traces, in conjunction with computer simulations, are used to estimate the normal and tangential force components at the interface to produce an estimate of the coefficient of friction. A preliminary estimate for a copper/steel interface is presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303681

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A modified Kolsky bar method consisting in the dynamic loading in shear of a pre-compressed thin-wall sample has been developed. The technique allows the identification of the transient response from static to kinetic friction under sliding velocities of about 2–6 m/s. The normal and tangential tractions are measured independently and hence a dynamic friction coefficient identified. The sliding velocities obtained with the Kolsky bar are smaller than those obtained in pressure-shear friction experiments. Hence, the techniques are complementary and provide valuable information for the formulation of friction laws at sliding velocities, pressures and temperatures typical of manufacturing processes, dynamic shear fracture, metal forming, etc. The friction properties of two nano-ceramics sliding against metals, cermets and other ceramics are here reported. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303682

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Composite plates, with and without, “waves” were made using improved explosive welding techniques. Oriented heat treatment of one surface of a steel-titanium composite introduces brittle intermetallic material at the specific interface. Currently, we are investigating methods to minimize this layer. While “waveless” interfaces revealed minimum intermetallic material; failure of the bond during ballistic impact necessitated production of a semi-compatible diffusion barrier using a fine layer of pure metal. Methods of producing composite plates with different interlayer materials and the effect of variables in optimizing the bond quality is presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303683

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper examines the effects of different nose-shaped projectiles on the perforation of concrete at high speeds [1]. The severity of damage is assessed in terms of the crater size on the impact and distal faces. An attempt is made to correlate the severity and type of damage with factors such as nose-shape of projectile and compressive strength of concrete. The energy absorbed during the perforation of concrete is also examined. A general trend of increase in severity of damage is observed when an ogive-shaped projectile as compared to a conical one is used. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303684

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Process of disturbance development on a contact boundary aluminum (AlMgZn alloy)—copper (M1 grade) at oblique impact in the initial stage—in the phase of a thrown plate acceleration was experimentally investigated. When plate flight base decreases fromd=1&hthinsp;mmtod=0.1&hthinsp;mm,we found that the disturbance amplitude at a contact boundary doesn’t convert into zero, but it gradually decreases froma=50–60&hthinsp;&mgr;m(d=1&hthinsp;mm)toa=15–20&hthinsp;&mgr;m(d=0.1&hthinsp;mm)and then it grows up toa=40–45&hthinsp;&mgr;m(d=0).A microcumulative jet in thin gaps(0⩽d⩽0.1&hthinsp;mm)accomplishes a reverse function, it doesn’t generate disturbances, but it stabilizes them. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303685

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present data on shock wave propagation in porous ice under conditions applicable to the outer solar system. The equation of state of porous ice under low temperature and low pressure conditions agrees well with measurements under terrestrial conditions implying that data on terrestrial snow may be applicable to the outer solar system. We also observe rarefaction waves from small regions of increased porosity and calculate release wave velocities. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303686

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Plate impact experiments have been performed on two igneous rocks of differing grain size. Shock stresses have been measured by means of embedded manganin stress gauges, up toca.12 GPa. In the coarser grained material data was obtained from both copper impactors on rock and the reverse situation. Results are compared and contrasted to the existing data for other geological materials. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303687

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Shock-recovery experiments have been performed on Berea Sandstone under dry and water-saturated conditions using a single-stage light-gas gun. Stress levels in the range between 3.1 and 9.8 GPa were achieved by impacting projectiles in a recovery fixture. The microstructural damage of the shocked samples were analyzed with scanning electron microscopy (SEM), laser particle analysis and X-ray computed micro tomography (XCMT). The dry samples show strongly and irregularly fragmented quartz grains with an considerably reduced porosity. In contrast, the water-saturated specimens have less grain damage and higher porosity. The water in the pores distributes the stresses which reduce the contact force between the grains during the shock compression. The dynamic fragmentation of the grain-grain interactions was modeled by explicitly treating the grain-pore structure using the Smooth Particle Hydrodynamic (SPH) computational method. This is a continuum Lagrangian gridless approach that features particles. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303688

出版商:AIP    

年代:1900

数据来源: AIP