A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Stress waves, deformation and fracture caused by liquid impact

1966 ◽  
Vol 260 (1110) ◽  
pp. 86-93 ◽  
Keyword(s):  
Surface Wave ◽  
High Speed ◽  
Rear Surface ◽  
Front Surface ◽  
Back Surface ◽  
High Speed Photography ◽  
Ring Fracture ◽  
Liquid Mass ◽  
Liquid Impact ◽  
The Impact

When a liquid mass strikes a solid surface, compressible behaviour, giving rise to a sharp peak of pressure, may occur in the initial stages of the impact. The duration of the peak depends on the dimensions and impact velocity of the liquid mass, and also on the compressional wave velocity for the liquid. There are similarities between this type of loading and that produced by the detonation of small quantities of explosive, since both give intense pressure peaks of only a few microseconds’ duration. The fracture and deformation of glasses, hard polymers, single crystal and ceramic materials by liquid impact at velocities up to 1000 m/s is described and briefly compared with that produced by solid/solid impact and explosive loading. The detailed development of fracture has been followed by high speed photography. In brittle solids the main characteristics of damage on the front surface is a ring fracture surrounding a largely undamaged area. The ring fracture forms at the edge of the loaded area where high tensile forces develop during impact. Outside this main ring of fracture short circumferential cracks occur; these are shown to be initiated by the Rayleigh surface wave at points where flaws existed. More complex fracture patterns which appear on the front surface of plates are due to the reinforcement of the surface wave with components of stress reflected from the back surface. Thin plate specimens often exhibit ‘scabbing’ fracture at the rear surface; in brittle materials of low attenuation this form of damage can be of prime importance. Since the stress pulses producing fracture during liquid impact are short the fractures themselves remain short and discrete. By a combination of impact loading and etching it is possible to investigate the distribution and depth of flaws, their role in the fracture process, and the effect which etching has upon them.

The brittle fracture of solids by liquid impact, by solid impact, and by shock

1964 ◽  
Vol 282 (1390) ◽  
pp. 331-352 ◽  
Keyword(s):  
Surface Wave ◽  
High Velocity ◽  
High Speed ◽  
Turbine Blades ◽  
Explosive Loading ◽  
Back Surface ◽  
High Speed Photography ◽  
Liquid Mass ◽  
Liquid Impact ◽  
The Impact

The type of stress pulse produced when a liquid mass strikes a solid at high velocity is first examined. Compressible behaviour, giving rise to a sharp peak of pressure, is found to occur in the initial stages of the impact. The duration of this peak depends on the dimensions and impact velocity of the liquid mass, and also on the compressible wave velocity for the liquid. A comparison is made with pulses produced by solid/solid impact and by the detonation of small quantities of explosive. Both the high-speed liquid impact and the explosive loading give intense pulses of duration only a few microseconds. A solid/solid impact has, by comparison, a much longer impact time of the order of hundreds of microseconds. The fracture of glasses and hard polymers using these three types of loading is described. The development of fracture is followed by high-speed photography. Differences in the modes of fracture are attributed to variations in the shape and duration of the applied stress pulses. Short circumferential fractures produced around the loaded area in liquid impact and explosive loading are shown to be initiated by the Rayleigh surface wave at points where flaws existed. More complex fracture patterns on the front surfaces of plates are due to the reinforcement of the surface wave with components of stress waves reflected from the back surface. A combination of impact loading and etching makes it possible to investigate the distribution and depths of flaws, their role in the fracture process, and the effect which etching has upon them. The observation on the deformation produced in solids by liquid impact has practical significance in the problem of supersonic aircraft flying through rain and in the erosion of turbine blades moving at high velocity through wet steam.

Studies of two-dimensional liquid-wedge impact and their relevance to liquid-drop impact problems

1985 ◽  
Vol 401 (1821) ◽  
pp. 225-249 ◽  
Keyword(s):  
High Speed ◽  
Liquid Drop ◽  
Time History ◽  
Drop Impact ◽  
High Speed Photography ◽  
Two Dimensional ◽  
Surface Geometry ◽  
Repeated Impact ◽  
Liquid Impact ◽  
The Impact

In the initial stage of liquid-drop impact, the contact region expands faster than the wave speed in the liquid. This causes compressible behaviour in the liquid, and high transient pressures. High-velocity jetting results when the wave motion in the liquid overtakes the expanding contact edge and moves up the free surface of the drop. The detailed pressure fields in this early time history of impact have been calculated by Lesser ( Proc . R . Soc . Lond . 377, 289 (1981)) for both two and three-dimensional liquid masses and for targets of finite admittance. An important result is that the edge pressures exceed the central ‘water-hammer’ pressure 3ρ 0 CU i and at the time of shock-detachment approach ca . 3ρ 0 CU i . At this stage the edge pressures, for both spherical drops and two-dimensional liquid wedges, depend only on the impact velocity and the instantaneous angle between the liquid and solid surfaces. This suggests that the essential features of the early stage of liquid impact can be usefully studied by producing impacts with two-dimensional liquid wedges, and predicted data for pressures, shock angles and velocities are presented. Experiments are described for producing impacts with preformed shapes by using water-gelatine mixtures and observing the impact events with high-speed photography. The results confirm the main features of the model and give information on edge pressures, jetting, cavitation in the liquid and the effect of the admittance of the solid. The relevance of the results to the damage and erosion of materials subjected to liquid impact is discussed. In particular, it is possible to explain the apparently low damage-threshold of some materials, the form of damage and its development with repeated impact. The study highlights the importance of the detailed surface geometry in the region of contact.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Conclusion

1966 ◽  
Vol 260 (1110) ◽  
pp. 311-315
Keyword(s):  
High Speed ◽  
Rear Surface ◽  
Peak Load ◽  
Brittle Materials ◽  
Front Surface ◽  
Drop Impact ◽  
Surface Flow ◽  
Steam Turbines ◽  
Brittle Solids ◽  
The Impact

Basic studies show that the measured impact pressure can be accounted for by assuming compressible deformation of the liquid drop in the first stages of impact. The distribution of pressure under a drop produces a shallow indentation in the surface of ductile solids and a ring fracture in brittle materials. The flow of liquid across the surface from under the drop leads to erosive shearing along the edges of the deformed area. Although in theory erosion due to surface flow would not occur on perfectly smooth surfaces, ideal conditions of this kind are impracticable. The smallest discontinuities (step heights down to about 1000 A) have been shown to act as nuclei for erosion pits. The short duration of the peak load during drop impact gives the impact an explosive character. In brittle materials the reflexion and interference of stress waves can cause extensive fracture in regions remote from the initial impact area. Spalling of the rear surface of a thin plate due to drop impact on the front surface could be an important mechanism in the failure of ceramic radomes in high speed aircraft and missiles. To some extent the strength of brittle solids can be improved by treatments which alter the size or number of surface flaws.

Hydraulic Performance and Jet Breakup Characteristics of the Impact Sprinkler with Circular and Non-circular Nozzles

2019 ◽  
Vol 35 (6) ◽  
pp. 911-924 ◽  
Author(s):  
Yue Jiang ◽  
Hong Li ◽  
Chao Chen ◽  
Lin Hua ◽  
Daming Zhang
Keyword(s):  
High Speed ◽  
Cone Angle ◽  
Hydraulic Performance ◽  
High Speed Photography ◽  
Breakup Process ◽  
Breakup Length ◽  
Jet Breakup ◽  
Circular Jets ◽  
Square Jets ◽  
The Impact

HighlightsThe hydraulic performance of the impact sprinkler with circular and non-circular nozzles were measured.A High-Speed Photography (HSP) technique was employed to extract the jet breakup process of the impact sprinkler.Two index equations of jet characteristic lengths and equivalent diameters of non-circular nozzles were fitted. Abstract. An experiment was carried out to investigate the hydraulic performance of an impact sprinkler by using circular and non-circular nozzles. A High-Speed Photography (HSP) technique was employed to extract the breakup process and flow behavior of low-intermediate pressure water jets issued from the different types of orifices. These orifices were selected by the principle of equal flowrate with the same pressure. Moreover, two characteristic lengths: the jet breakup length and the initial amplitude of surface wave were measured. It was found that the sprinkler with circular nozzles produced the largest radius of throw followed by square nozzles and regular triangular nozzles when the cone angle of nozzle and pressure were unchanged, while the sprinkler with regular triangular nozzle had the best variation trend of water distribution and combination uniformity coefficient. Regular triangular jets exhibited a higher degree in breakup and the shortest breakup length compared with the square jets and the circular jets. The initial amplitudes of surface waves of regular triangular jets were larger than the square jets and the circular jets with the same cone angle. Two index equations of jet characteristic lengths and equivalent diameters of both circular and non-circular orifices were fitted with a relative error of less than 10%, which means the fitting formulas were accurate. Keywords: Breakup length, Fitting formula, Hydraulic performance, Initial amplitude, Non-circular jets.

scholarly journals Experimental investigation of the impact response of novel steelbiocomposite hybrid materials

2018 ◽  
Vol 183 ◽  
pp. 02040
Author(s):  
KarthikRam Ramakrishnan ◽  
Mikko Hokka ◽  
Essi Sarlin ◽  
Mikko Kanerva ◽  
Reijo Kouhia ◽  
...  
Keyword(s):  
High Speed ◽  
Structural Integrity ◽  
Metal Layer ◽  
Rear Surface ◽  
Impact Resistance ◽  
Natural Fibre ◽  
Image Correlation ◽  
Impact Response ◽  
High Speed Camera ◽  
The Impact

Recent developments in the production of technical flax fabrics allow the use of sustainable natural fibres to replace synthetic fibres in the manufacture of structural composite parts. Natural fibre reinforced biocomposites have been proven to satisfy design and structural integrity requirements but impact strength has been identified as one of their limitations. In this paper, hybridisation of the biocomposite with a metal layer has been investigated as a potential method to improve the impact resistance of natural fibre composites. The impact response of biocomposites made of flax-epoxy is investigated experimentally using a high velocity particle impactor. A high-speed camera setup was used to observe the rear surface of the plates during impact. Digital Image Correlation (DIC) of the high speed camera images was used for full-field strain measurement and to study the initiation and propagation of damage during the impact. The different modes of damage in the hybrid laminate were identified by postimpact analysis of the section of the damaged composite plate using optical microscopy. The study shows the difference in impact response for different material combinations and configurations. The hybrid construction was shown to improve the impact resistance of the flax composite.

scholarly journals Dynamic damage in carbon-fibre composites

2016 ◽  
Vol 374 (2071) ◽  
pp. 20160018 ◽  
Author(s):  
N. K. Bourne ◽  
S. Parry ◽  
D. Townsend ◽  
P. J. Withers ◽  
C. Soutis ◽  
...  
Keyword(s):  
Carbon Fibre ◽  
High Speed ◽  
Failure Modes ◽  
Structural Integrity ◽  
High Speed Photography ◽  
Compression Phase ◽  
Impact Surface ◽  
Fibre Composites ◽  
The Impact ◽  
Carbon Fibre Composites

The Taylor test is used to determine damage evolution in carbon-fibre composites across a range of strain rates. The hierarchy of damage across the scales is key in determining the suite of operating mechanisms and high-speed diagnostics are used to determine states during dynamic loading. Experiments record the test response as a function of the orientation of the cylinder cut from the engineered multi-ply composite with high-speed photography and post-mortem target examination. The ensuing damage occurs during the shock compression phase but three other tensile loading modes operate during the test and these are explored. Experiment has shown that ply orientations respond to two components of release; longitudinal and radial as well as the hoop stresses generated in inelastic flow at the impact surface. The test is a discriminant not only of damage thresholds but of local failure modes and their kinetics. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

Full scale field testing of temporary rockfall protection measures

2020 ◽  
Author(s):  
Axel Volkwein ◽  
Florian Hofstetter ◽  
Marc Hauser
Keyword(s):  
High Speed ◽  
Minimum Weight ◽  
Field Tests ◽  
Front Surface ◽  
Frame Rate ◽  
Slope Surface ◽  
Retention Capacity ◽  
Protection Measures ◽  
The Impact ◽  
Rockfall Protection

<p>Temporary rockfall protection measures are often implemented by using so-called steel palisades. Such elements can described as a steel surface that is supported perpendicular to the slope surface. In the present case, several sheet piling sections are welded onto a steel frame to form an area 1.5m high and 3m long. At the lateral edges of the surface, steel sections, welded together to form a triangle, create the support of the front surface, so that one side of the triangle is parallel to the impact surface and another side is parallel to the slope surface. At the corners close to the ground, massive steel spikes allow penetration into the ground. The weight of a palisade is about 900kg. An example of such a palisade can be found in [1].</p><p>The above barriers are in usage since many years. However, their rockfall energy retention capacity has never been evaluated yet. For that reasons, the Swiss Federal Railways launched a project for a deeper understanding of the performance of the palisades; for an adequate selection of the protection measures and a reliable risk analyses with respect to the variety of rockfall events that can be expected at a specific construction site and might cause failure of a structure.</p><p>Failure limits of the palisades are expected regarding the following failure scenarios:</p><ul><li>tilting of the barrier over the valley side steel spikes</li> <li>displacement of the barrier due to insufficient action of the steel spikes</li> <li>failure of the front surface</li> </ul><p>In this contribution, the above mechanisms are evaluated by means of 1:1 field tests.  A detailed analysis of performance and failure states will be provided. Furthermore, potential solutions for simple but effective reinforcement of the barriers are discussed.</p><p>The field tests were carried out on a slope inclined at an angle of about 30 degrees. Test blocks with a minimum weight of 240kg are thrown onto the palisades with the help of a forestry cableway reaching impact speeds of up to 25m/s. The impact energies vary from 12 to 100 kJ. Impact location and impact speed are determined by means of laterally taken high-speed video records with a frame rate of up to 1000fps and a resolution of 800x600pxs. Furthermore, the accelerations in the test body were measured at 1000Hz and – for some of the tests - the acting anchorage forces at 5000Hz.</p><p> </p>

A New Concept of Needle-Free Jet Injector by the Impact Driven Method

2017 ◽  
Vol 11 (1) ◽  
Author(s):  
Prachya Mukda ◽  
Kulachate Pianthong ◽  
Wirapan Seehanam
Keyword(s):  
High Speed ◽  
Liquid Jet ◽  
High Speed Photography ◽  
Free Jet ◽  
Impact Peak ◽  
Lower Pain ◽  
Jet Velocity ◽  
Commercial Device ◽  
Jet Injectors ◽  
The Impact

Currently, most of commercial needle-free jet injectors generate the liquid jet by a method called “driving object method” (DOM); however, the reliability and efficiency are still questioned. This paper proposes a new concept of jet generation method, known as “impact driven method” (IDM). A prototype of an IDM jet injector is designed, built, tested, and compared to a commercial device (Cool.click, Tigard, OR). Fundamental characteristics, i.e., the exit jet velocity and impact pressure, are measured. Jet injection processes are visualized both in air and in 20% polyacrylamide by high speed photography. In this study, from the prototype of the IDM jet injector, a maximum jet velocity of 400 m/s and impact peak pressure of 68 MPa can be obtained. It is clear that the IDM jet injector provides a double pulsed liquid jet, which is a major advantage over the commercial jet injector. Because, the first pulse gives a shorter erosion stage, and then, immediately the second pulse follows and provides a better penetration, wider lateral dispersion, and considerably less back splash. Hence, lower pain level and higher delivery efficiency should be achieved. It can be concluded that the IDM concept is highly feasible for implementation in real applications, either for human or animal injection. However, the control and accuracy of IDM still needs to be carefully investigated.

Behavior of Soft Spheres During Impact by High-Speed Photography

1983 ◽  
Vol 105 (1) ◽  
pp. 67-73 ◽  
Author(s):  
Yoichi Tatara
Keyword(s):  
Deformation Process ◽  
High Speed ◽  
High Impact ◽  
High Speed Photography ◽  
Tennis Ball ◽  
Hertz Model ◽  
Hertz Theory ◽  
Soft Spheres ◽  
Almost All ◽  
The Impact

Previously, it has been verified experimentally for durations of impact that the Hertz theory (the quasi-statical theory) holds during impact of spheres without any exception. However, no measurement of duration of impact has been presented for spheres of materials other than metal. This study presents exceptional cases of impacts of spheres during which the Hertz model does not directly hold. By the use of a high-speed camera running at a speed of 5000 frames/s, durations of impact are measured directly for impacts of two solid rubber spheres of the same size and content and impacts of a soft ball (Japanese type-soft tennis ball) on a rigid foundation. As a result, the measured durations of impact in the two impacting cases are found to be decreased as the impact velocity is increased, similar in tendency to durations of impact of elastic metal spheres during which the Hertz theory holds. However, the measured durations of impact are found to be clearly shorter than results calculated according to the Hertz theory, approximately half in the former impacts at high impact velocities, and about 70 percent of the Hertzian results in the latter impacts at almost all impact velocities. Deformation process of the ball impacting on the foundation is also presented to indicate both durations in the compressive process and the restitution one to be shorter than those expected by the Hertz theory. The other results observed on the films are noted to investigate the origin of the great discrepancies between the measured and Hertzian durations (that is, the impacting mechanism of the rubber spheres or the rubber ball packed with air treated here).

High-speed infrared thermal imaging during ballistic impact of triaxially braided composites

2018 ◽  
Vol 52 (25) ◽  
pp. 3549-3562 ◽  
Author(s):  
Joel P Johnston ◽  
J Michael Pereira ◽  
Charles R Ruggeri ◽  
Gary D Roberts
Keyword(s):  
Thermal Imaging ◽  
High Speed ◽  
Imaging System ◽  
Polymer Matrix Composites ◽  
Ballistic Impact ◽  
Back Surface ◽  
Composite Panels ◽  
Infrared Thermal Imaging ◽  
Failure Patterns ◽  
The Impact

Ballistic impact experiments were performed on triaxially braided polymer matrix composites to study the heat generated in the material due to projectile velocity and penetration damage. Triaxially braided (0/+60/−60) composite panels were manufactured with T700S standard modulus carbon fiber and two epoxy resins. The PR520 (toughened) and 3502 (untoughened) resin systems were used to make different panels to study the effects of resin properties on temperature rise. The ballistic impact tests were conducted using a single stage gas gun, and different projectile velocities were applied to study the effect on the temperature results. Temperature contours were obtained from the back surface of the panel during the test through a high speed, infrared thermal imaging system. The contours show that high temperatures were locally generated and more pronounced along the axial tows for the T700S/PR520 composite panels; whereas, tests performed on T700S/3502 composite panels, using similar impact velocities, demonstrated a widespread area of lower temperature rises. Nondestructive, ultrasonic C-scan analyses were performed to observe the failure patterns in the impacted composite panels and correlate the C-scan results with the temperature contours. Overall, the impact experimentation showed temperatures exceeding 252℃ (485°F) in both composites which is well above the respective glass transition temperatures for the polymer constituents. This expresses the need for further high strain rate testing with measurement of the temperature and deformation fields in order to fully understand the complex behavior and failure of the material and to improve the confidence in designing aerospace components with these materials.

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