Tham khảo tài liệu 'mechanics of solids 2011 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1-126 Section 1 FIGURE Accelerometer data from front suspension system of vehicle. Logarithmic decrement 9 ln x1 x2 damping ratio . Defining Terms STATICS Equilibrium A concept used to determine unknown forces and moments. A rigid body is in equilibrium when the equivalent force-couple system of the external forces acting on it is zero. The general conditions of equilibrium are expressed in vector form EF 0 EM E r X F 0 or scalar form Fx 0 TFy 0 IF 0 lMx 0 lMy 0 iw 0 . Equivalent force-couple system Any system of forces and moments acting on a rigid body can be reduced to a resultant force and a resultant moment. Transformations of a force-couple system involving chosen points of reference are easy to make. These are useful for determining unknown forces and moments and the critical locations in structural members. Free-body diagram A method of modeling and simplifying a problem for the efficient use of the equilibrium equations to determine unknown forces and moments. A body or group of bodies is imagined to be isolated from all other bodies and all significant external forces and moments known or unknown are shown to act on the free-body model. PLATE 1 Flat-Trac Roadway Simulator R D 100 Award-winning system in 1993. Photo courtesy MTS Systems Corp. Minneapolis MN. PLATE 2 Spinning torque transducer with on-board preamplifier. An angular accelerometer is attached at the center of the torque cell. Photo courtesy MTS Systems Corp. Minneapolis MN. 1999 by CRC Press LLC PLATE 3 Vibration screening of a circuit board using an electromagnetic shaker and a laser doppler vibration pattern imager. Photo courtesy Ometron Inc. Sterling VA. PLATE 4 Vibration patterns of a computer hard disc reader head at 4540 Hz. Photo courtesy Ometron Inc. Sterling VA. 1999 by CRC Press .