Machine Design Practice Test: Wire Ropes Stresses, Buckling of Columns — Flashcards

Wire ropes are stressed by:
Direct stress: The weight of the rope and the axial load lifted
Bending stress: When the rope winds around the sheave or drum
Stresses during starting and stopping
Stress due to change in speed
Effective stress 

Wire ropes are also stressed by fluctuating forces, wear, corrosion, and in rare cases, extreme forces. 
Some typical failure modes of wire ropes include: Fracture, Wear, Corrosion, Geometric failure, Thermal failure. 

The stress at the middle cross section of wire rope is symmetrically distributed. The average stress level of IWS is higher than that of SSs, and the overall stress level of PCWR is higher than that of LCWR. 
Abnormal tensile or torsional stresses in a wire rope will cause abnormal tensile stress in the wire rope. However, the treatment methods for these two stresses are different. 

Buckling of columns is a phenomenon that occurs when a slender structural element, such as a column or a beam, fails under compressive loads. It is characterized by sudden, lateral deflection or bending. 

Buckling is caused by: Material strength and stiffness properties, Instability, Geometric failure 

The most suitable column design to withstand buckling is one with a homogeneous cross-section and initial straightness. 

There are different types of buckling, including:
Flexural-torsional buckling: A combination of bending and twisting response of a member in compression. This can occur in columns with open cross-sections.
Lateral-torsional buckling: Can occur in simply supported beams loaded in bending. 
The Euler formula is used to analyze the buckling of long columns with loads applied along the central axis. The Johnson formula is used to analyze the buckling of intermediate columns.