| 1. |
- Beccu, E., et al.
(författare)
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Efficiency of percussive drilling of rock with dissipative joints
- 1990
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 9:3, s. 277-287
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear dissipative spring mass (NDSM) model for a percussive drill rod joint of the coupling sleeve (CS) type has been implemented into a Modula-2 program with the aid of which percussive drilling of rock is simulated. Transmission and dissipation of energy are first studied when a rectangular stress wave, generated through the impact by a uniform hammer, is transmitted through a single joint. The efficiency of energy transmission increases from 81 to 94% and the relative energy dissipation decreases from 8 to 1 or 2% when the length of the hammer varies from relatively short to relatively long. The effect of the joint preload is weak in the range from medium to relatively high preload. The efficiency of the percussive drilling process decreases with the number of joints but depends little on the joint preload. For soft rock, the efficiency increases with hammer length, whereas for medium and hard rock the dependence of efficiency on hammer length is not monotonic. This is because soft rock requires a long incident wave for efficient conversion of energy to work at the bit, whereas the reverse is true for hard rock. It is also found that the efficiency of the percussive drilling process may be considerably underestimated if the effects of each joint on the length and shape of the transmitted wave and of multiple reflections within the drill string are neglected
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| 2. |
- Beccu, R., et al.
(författare)
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Transmission and dissipation of stress wave energy at a percussive drill rod joint
- 1987
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 6:3, s. 157-173
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Tidskriftsartikel (refereegranskat)abstract
- Transmission and dissipation of stress wave energy at a percussive drill rod joint is determined for three joint types, three joint preload levels, three hammer lengths ( incident wave lengths) and a range of impact velocities ( incident wave amplitudes). The energies of the incident, reflected and transmitted waves are evaluated from measured strains, and then the dissipated energy is determined as the deficit of energy in the two latter waves compared with the first. The accuracy needed is obtained by introducing a compensation factor and determining its value from the requirement of momentum conservation. The experimental results for threaded standard joints are compared with experimental results for threadless dummy joints, made in one piece, and also with theoretical results. The latter are based on one model which represents the joint as a well on a one- dimensional elastic rod (characteristics impedance or CI model) and on another model which represents the joint as a rigid mass between one-dimensional elastic rods (rigid mass or RM model). For the joints 70-100% of the incident wave energy is transmitted and 0-20% is dissipated. The corresponding figures for the dummies are 90-100% and (±)1%, repectively. The latter figure indicates the inaccuracy in the measurement and evaluation procedures. The two models agree fairly well with the dummies. Under certain conditions they also give reasonably accurate predictions for the energy transmitted through a joint. As they sometimes give quite inaccurate results for energy transmission and furthermore fail to predict energy dissipation they need be refined.
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| 3. |
- Juntikka, Rickard, et al.
(författare)
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Weight-balanced drop test method for characterization of dynamic properties of cellular materials
- 2004
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 30:5, s. 541-554
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Tidskriftsartikel (refereegranskat)abstract
- A novel weight-balanced drop rig used to evaluate the response of cellular materials subject to dynamic compression is presented. The testing method utilizes approximately constant velocity throughout the major part of the compression phase and the results compare well with results from other methods, reported in the literature. The repetitiveness is excellent, the rig is simple and the results are easily extracted. The applicability of the method for determination of elastic modulus is however limited to materials with relatively low stiffness. Accurate modulus measurements for stiff materials at high strain-rates require a very rigid and lightweight test set-up.
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| 4. |
- Lundberg, Bengt, et al.
(författare)
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Nonlinear dissipative spring mass model for a percussive drill rod joint of the coupling sleeve type
- 1989
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 8:4, s. 303-313
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear dissipative spring mass (NDSM) model for a percussive drill rod joint of the coupling sleeve (CS) type is established. Such a joint consists of a cylindrical coupling sleeve with internal thread which connects two drill rods with external threads at their ends. The model disregards wave motion in the coupling sleeve but accounts for axial mobility of the sleeve relative to the rods. This mobility is due to local deformation and slip of the threads. The model is characterized by the mass of the sleeve and by three parameters which represent the coupling between the sleeve and the drill rods through the threads. A static and a dynamic test have been developed for determining the coupling parameters. The model is validated by simulating previous impact tests with a commercial CS joint.
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| 5. |
- Lundberg, Patrik, et al.
(författare)
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Impact of metallic projectiles on ceramic targets : transition between interface defeat and penetration
- 2000
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 24:3, s. 259-275
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Tidskriftsartikel (refereegranskat)abstract
- Armour systems capable of defeating an incoming projectile on the surface of a ceramic have been reported by several authors. This capability, called interface defeat, signifies that the projectile material is forced to flow radially outwards on the surface of the ceramic without penetrating significantly. In order to investigate the conditions for interface defeat, two models for the interaction of a metallic projectile and a ceramic target were established. With the aid of them, upper and lower bounds for the transition impact velocity between interface defeat and normal penetration were estimated for a given combination of metallic projectile and ceramic target. These approximate bounds were found to be consistent with transition velocities determined experimentally for two projectile materials (tungsten and molybdenum) and five target materials (two types of silicon carbide, boron carbide, titanium diboride and a polycrystalline diamond composite).
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| 6. |
- Lundberg, Patrik, et al.
(författare)
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Influence of scale on the penetration of tungsten rods into steel-backed alumina targets
- 1996
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 18:4, s. 403-416
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Tidskriftsartikel (refereegranskat)abstract
- As ballistic tests are often performed in reduced geometrical scale, the scaling laws are important for the interpretation of the results. In this study, we tested the validity of replica scaling, by which we mean that all geometrical dimensions are scaled uniformly, while the materials and the impact velocity are kept the same. Long tungsten projectiles with length-to-diameter ratio 15 were fired against unconfined alumina targets with steel backing. The tests were carried out with impact velocities 1500 m s−1 and 2500 m s−1, and in three different scales with projectile lengths 30, 75 and 150 mm (diameters 2, 5 and 10 mm). The alumina targets were photographed by means of a high-speed camera, and the tungsten projectiles were photographed inside the alumina targets by means of flash radiography. Also, the residual penetrations in the steel backings were measured. The Johnson-Holmquist model for ceramic materials was implemented into the AUTODYN code, which was used for simulation of the experiments. The agreement between results of experiment and simulation was fair, and over the tested interval of scales replica scaling was found to be valid with reasonable accuracy.
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| 7. |
- Nordlund, Erling, et al.
(författare)
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Slip and energy dissipation in conical friction joints loaded by impact-induced waves
- 1986
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 4:2, s. 127-144
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Tidskriftsartikel (refereegranskat)abstract
- Conical friction (CF) joints subjected to impact-induced wave (IIW) loading are studied theoretically and experimentally. The system considered consists of a long, straight, cylindrical and linearly elastic rod which is impacted axially at one end, and which has a body attached by means of a CF joint at the opposite end. The conditions are such that the wave propagation is 1-D in the rod and can be neglected in the attached body, which is therefore treated as rigid. Slip and energy dissipation in the CF joint due to a single IIW load are determined as functions of four dimensionless parameters which represent the duration of the incident wave, the mass of the attached body, the behaviour of the CF joint and the initial slip due to a compressive preload. The conditions under which detachment occurs are also found. Results for repeated noninteracting IIW loads are derived from those obtained for a single IIW load. The theoretical results exhibit phenomena which may sometimes have a spectacular appearance. For example, four consecutive and identical IIW loads may have the effect of fastening, loosening, fastening again and, finally, detaching the CF joint. There is a fair agreement between theoretical and experimental results.
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| 8. |
- Nordlund, Erling
(författare)
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Slip and energy dissipation in cylindrical friction joints loaded by impact-induced waves
- 1987
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 6:1, s. 35-50
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Tidskriftsartikel (refereegranskat)abstract
- Cylindrical friction (CYLF) joints subjected to impact-induced wave (IIW) loading are studied theoretically and experimentally. The system considered consists of a long, straight, cylindrical and linearly elastic rod which is impacted axially at one end by a cylindrical and linearly elastic hammer. A body is attached at the other end by means of a CYLF joint. The conditions are such that the wave propagation is 1-D in the hammer and the rod and can be neglected in the attached body which is therefore treated as rigid. The agreement between numerical and analytical solutions is good. There is also fair agreement between theoretical and experimental results.
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| 9. |
- Westerling, Lars, et al.
(författare)
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Tungsten long-rod penetration into confined cylinders of boron carbide at and above ordnance velocities
- 2001
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 25:7, s. 703-714
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to investigate the influence of impact velocity and confinement on the resistance of boron carbide targets to the penetration of tungsten long-rod projectiles. Experimental tests with impact velocities from 1400 to 2600 m/s were performed using a two-stage light-gas gun and a reverse impact technique. The targets consisted of boron carbide cylinders confined by steel tubes of various thicknesses. Simulations were carried out using the AUTODYN-2D code and Johnson–Holmquist's constitutive model with and without damage evolution. The experimental results show that the penetration process had different character in three different regions. At low-impact velocities, no significant penetration occurred. At high-impact velocities, the relation between penetration velocity and impact velocity was approximately linear, and the penetration was steady and symmetrical. In between, there was a narrow transition region of impact velocities with intermittent and strongly variable penetration velocity. In the lower part of this region, extended lateral flow of the projectile took place on the surface of the target. The influence of confinement on penetration velocity was found to be small, especially at high-impact velocities. The simulated results for penetration velocity versus impact velocity agreed fairly well with the experimental results provided damage evolution was suspended below the transition region.
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| 10. |
- Ödéen, Sven, et al.
(författare)
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Prediction of impact force by impulse response method
- 1991
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 11:2, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- A method has been established which permits prediction of impact force history from the velocity response of each impacting body to an impulsive force applied to its impact face, and the impact velocity. The bodies may consist of one or several linearly elastic or viscoelastic materials. However, the method is limited to cases of impact without significant effects of friction and slip, with constant contact area and with small deformations. It has been applied to four cases of axial impact of a truncated cone or a compound cylinder on a long cylindrical rod. The truncated cone was made of Nylon-6, the compound cylinder of Nylon-6 and aluminum, and the long cylindrical rod of steel. For the truncated cone and the compound cylinder, measured as well as theoretically predicted impulse responses were used, while for the long cylindrical rod only a theoretically predicted impulse response was employed. In all cases good agreement was obtained between the impact force histories predicted, using the impulse response method, and those measured with the aid of strain gauges on the long cylindrical rod. Because of three-dimensional effects the best agreement was obtained for the predictions based on measured impulse responses for the truncated cone and the compound cylinder
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