汽车座椅资料-Report-1332(英文版).doc

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REPORT 1332
SEAT DESIGN FOR CRASH
WORTHINESS
By I.IRVING PINKEL and EDMUND
G.ROSENBERG
SUMMARY
A study of many crash deceleration records suggested a
simplified model of a crash deceleration pulse, which incorporates the essential properties of the pulse. The model pulse is considered to be
composed of a base pulse on which are super-imposed more
secondary pulses of shorter duration. The results of a mathematical analysis of the seat-passenger deceleration in response to the airplane deceleration pulse are provided. On the basis of this information presented as working charts, the maximum deceleration loads experienced by the seat and passenger in response to the airplane deceleration pulse can be computed. This maximum seat-passenger deceleration is found to depend on the natural frequency of the seat containing the passenger, considered as a mass-spring system.
Seat failure is considered to be a progressive process, which begins when the seat is deformed beyond the elastic limit. Equations are presented that relate the energy available to deform the seat beyond the elastic limit to the maximum seat-passenger deceleration,

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seat natural frequency, and seat strength. A method is presented that
shows how to arrive at a combination of seat strength, natural frequency, and ability to absorb energy in deformation beyond the elastic limit that will allow the seat to serve without failure during an airplane deceleration pulse taken as the design requirement. The qualities of the seat can be obtained from measurements made under static conditions.
Data are presented from full-scale laboratory and crash studies on the deceleration loads measured on dummy passengers in seats of standard and novel design. The general trends indicated by theory are obtained.

INTRODUCTION
Crash measurements show that the deceleration imposed on a seat in a
crash is highly irregular, and the question raised is "What is the relation
between the properties of a seat measured under static conditions and its
ability to hold the passenger through a deceleration?" This paper is concerned
principally with the answer to this question.
Crash measurements showed periods of high deceleration lasting for several tenths of a second separated by longer time intervals during which the deceleration was below 3 or 4 g's. Seat failure will usually occur during the
short-duration high-deceleration phase of the crash. For this reason, interest in this report centers on this high-deceleration phase, A typical crash record of the high-deceleration period is show in figure 1(a).Its highly oscillatory and irregular character is apparent.
The seat is the structural link between the fuselage floor and the passenger. The force required to decelerate the passenger is applied by the seat, usually through the seat belt or seat back. If the passenger were fastened rigidly to the seat and the seat rigidly to the floor, then the passenger, seat, and floor would move as a unit, he deceleration shown in figure 1,measured on the floor, would appear everywhere on the seat and passenger. The seat deceleration loads would be known at once from the
measured floor deceleration. If the peak deceleration there were 10 g's and the seat
were designed for 12 g's, the seat would be working within safe limits. Actually,
however, the seat is not rigid. It is made of flexible members. Also, the passenger is

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often loosely connected to the seat at the moment of the crash.
Seat flexibility is considered first, and the passenger is assumed tightly coupled to the seat. The passenger and the seat form a mass-spring system indicated schematically in figure 2 (a).The pedestal of the seat forms the spring attached to the floor, and the passenger constitutes the mass. When the passenger sits lightly in the seat, it has its normal shape. However, when the seat restrains the passenger with a large holding forces in a crash, the seat is distorted, as shown in exaggerated form in figure 2 (b). The holding force F on the passenger grows as shown in figure 3 as the
seat is distorted. The straight-line portion of the curve is given by the expression
F = kx (1)
Where k is the elastic constant of the seat and x is the seat distortion. The significant
fact is that the passenger-holding force develops as the seat distorts, and this distortion takes time to grow.
For the purpose of this report, the design strength of the seat is defined as the

force Fd that distorts the seat to its elastic limit xd . This term xd is called the
design distortion. As long as the seat distortion remains within the elastic limit, it will

return to its original shape when the holding force F is relieved. If xd is exceeded,
the seat is permanently deformed. The process of seat failure has begun. Seat failure is
considered to be a progressive process in which the permanent deformation of the seat grows to the point where the link between the passenger and the floor broken.
The design strength of a seat is often quoted in terms of the passenger deceleration the seat will hold, expressed in gravitational units. If m is the mass of the

passenger, then the design strength of the seat As,d expressed in gravitational units is

As,d = Fd / m , where Fd is given in pounds-force and m is given in pounds-mass.
For simplicity, the seat is taken to be without mass compared with the passenger, who
is assumed to weigh 200 pounds. The seat distortion x is measured at the point of application of the passenger-holding force. For a forward-facing passenger, this point is the seatbelt-attachment fitting on the seat. For a rearward-facing passenger, the holding force is distributed over the seat back as shown in figure 2 (b). The point at which the seat distortion should be measured is determined by the moment of the
passenger's mass with respect to the seat floor attachment. This point is
approximately 1 foot above the seat pan in the rearward facing seat.
Data indicate that the natural frequency of a seat of the light construction used in aircraft and carrying a 200-pound passenger would be less than 20 cycles per second. From theory it is known that spring-mass systems having this low natural frequency will not move appreciably in response to the high-frequency components of the floor deceleration, which are of the order of 100 cycles per second in figure 1 (a).
If these unimportant high-frequency oscillations in the deceleration trace are filtered out and only those oscillations up to 50 cycles per second remain, the prominent features of the deceleration trace become evident (fig. 1 (b)).The main

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