tailieunhanh - Harris' Shock and Vibration Handbook Part 14

Tham khảo tài liệu 'harris' shock and vibration handbook part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | SHOCK AND VIBRATION ISOLATORS AND ISOLATION SYSTEMS been occasionally used for shock isolation systems. However in general tension loading is not recommended because of the resulting loads on the elastomer-to-metal bond which may cause premature failure of the material. Buckling Loading. Buckling loading illustrated in Fig. occurs when the externally applied load causes an elastomeric element to warp or bend in the direction of the applied load. Buckling stiffness characteristics may be used to derive the benefits of both softening stiffness characteristics for the initial part of the load-deflection curve and hardening characteristics for the later part of the load-deflection curve . The buckling mode thus provides high energy-storage capacity and is useful for shock isolators where force or acceleration transmission is important and where snubbing . motion limiting is required under excessively high transient dynamic loads. This type of stiffness characteristic is exhibited by certain elastomeric cushioning foam materials and by specially designed elastomeric isolators. However it is important to note that even simple compressive elements will buckle when the slenderness ratio the unloaded length width ratio exceeds . Combinations of the types of loading described above are commonly used which result in combined load-deflection characteristics. Consider for example a compression-type isolator which is installed at an angle instead of in the usual vertical position. Under these conditions it acts as a compression-shear type of isolator when loaded in the vertical downward direction. When loaded in the vertical upward direction it acts as a shear-tension combination type of isolator. Static and Dynamic Stiffness. When the main load-carrying spring is made of rubber or a similar elastomeric material the natural frequency calculated using the stiffness determined from a static load-deflection test of the spring almost invariably gives a value lower .