Impact duration

The simplest theory of impact, known as stereomechanics, deals with the impact between rigid bodies using the impulse-momentum law. This approach yields a quick estimation of the velocity after collision and the corresponding kinetic energy loss. However, it does not yield transient stresses, collisional forces, impact duration, or collisional deformation of the colliding objects. Because of its simplicity, the stereomechanical impact theory has been extensively used in the treatment of collisional contributions in the particle momentum equations and in the particle velocity boundary conditions in connection with the computation of gas-solid flows. 

Collisions between particles with smooth surfaces may be reasonably approximated as elastic impact of frictionless spheres. Assume that the deformation process during a collision is quasi-static so that the Hertzian contact theory can be applied to establish the relations among impact velocities, material properties, impact duration, elastic deformation, and impact force. 

FIGURE 53.1 Whole-body human tolerance to vehicle acceleration based on impact duration. (Redrawn from Eiband A.M. Human Tolerance to Rapidly Applied Acceleration. A Survey of the Literature. National Aeronautics and Space Administration, Washington DC, NASA Memo No. 5-19-59E, 1959 and Viano D.C., Bull NY Acad. Med., 2nd Series, 64 376-421,1988. With permission.)... 

Material properties. In addition to the common knowledge that the materials must be stronger, tougher, and lighter [79], it is envisioned that the materials must be less stiff during impact so that the impact duration can be extended and the elastic wave will have sufficient time to reach and be reflected by the boundary many times for a quasi-static response, as discussed by Olsson [76]. However, this requirement is contradictory to the structural requirement that is, the material must be stiff to provide structural capacity. 

Very short impact duration and very small mass... 

Data on the structure density increase resulting from microbiological impact are confirmed by the data obtained by EPR spectroscopy by radical probe correlation time [1], The radical probe mobility decreases with the increase of microbiological impact duration. This may testify to packing of the leather tissue structure as a result of microflora impact on the material. 

The vector w projects the impact force from the normal direction of the impact on the direction of the generalized coordinates. Due to the assumption of infinitesimal impact duration, the velocity changes in a jump, whereas the position remains unchanged. The equation of motion during impact is then formulated on velocity level. 

The only difference between CCH and FEMA 55 resides in the recommended values for the impact duration which has a noticeable effect on the magnitude of the force. For example, CCH recommends the use of impact duration of 0.1s for concrete structmes, while FEMA 55 provides different values for walls and piles for various construction types as shown in Table 11.1. 

Table 11.1. Impact duration of floating debris (FBMA 55).

To calculate debris impact, a mass of 455 kg is used to represent a floating object at the water surface. The mass used is consistent with the recommendations of CCH and FEMA 55. In this example, it is assumed that the debris will impact a single reinforced concrete column. CCH assumes a duration of 0.1 s for concrete structures. FEMA 55 recommends an impact duration ranging from 0.3 to 0.6 s for reinforced concrete piles or columns. Hence, impact duration of 0.3 s is assumed in the design example. 

ABSTRACT Intermodal transport is a complicated way of transportation, where there is usually over a dozen means of transportation and many modes of transportation. As can be easily seen cargo is subjected redoubled number of transshipments in comparison to the number of vehicles, which is transported. Very popular transport relation Asia—Europe shipping takes around 25 days, while terminal operations take up 17% of the time transferring cargo container. In all decisive importance to the planning of operations to plan the operation of machinery— planning is affected by the resulting time. The purpose of this article is to demonstrate the direct impact duration elements of the service on the total time of the process. 

It is well recognized that a head impact produces both translational and rotational motion as well as deformation of the skull. Resultant brain injury may occur from both absolute motion of the brain and its relative displacement with respect to the skull. At present, there are several physical parameters used in the evaluation of head injury, including translational and/or rotational acceleration levels of head impact, impact force, velocity and kinetic energy, impulse and impact duration, etc. These measures have been widely used for animal, human cadaver, and dummy experimental data to determine tolerable and survival thresholds for head impact in translation or rotation. Other parameters such as skull displacement and stresses, brain pressures and strains, as well as neck stretch/strain are usually related to analytical and experimental head model studies. 

A hammer of mass m = 10(X) kg falls from a height h = 2m onto an anvil. Impact duration is t = 0.01 sec. Determine the average value of the impact force. 

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