Mechanical Design Handbook

Figure 1: Buckling is a geometric instability failure, not just a material strength failure. In a mechanical design situation, the expected load on a column and its length are usually known. The designer's job is to specify the structural parameters to prevent failure. Advertisement The 5 Key Design Parameters End Fixity: How is the column attached? (Pinned-Pinned, Fixed-Free, etc.) This determines the effective length factor (K). Cross Section: The shape (I-beam, Tube, Solid Round). This determines the Radius of Gyration (r). Material: Determines Stiffness (Modulus E) and Strength (Yield Sy). Design Factor (N): The safety margin. Final Dimensions: The actual width/thickness required. Because the cross-section (Item 2) determines the slenderness ratio, but you can't pick the cross-section until you know the allowable stress, column design is inherently iterative . The Iterative Design Loop: 1. Assume a di...

Reactions are the forces and/or couples acting at the supports and holding the beam in place. In some cases, the user should enter a distributed load to account for the weight of the beam. The shear V effective on a section is the algebraic sum of all forces acting parallel to and on one side of the section: V = Σ F Advertisement The bending moment is the algebraic sum of the moments due to applied loads and other applied moments to one side of the section of interest. Using the value V , the bending moment can be calculated: M = ∫ (V · dx) + M 0 Where: • x = position on the beam measured along its length • M 0 = constant of integration evaluated from the boundary conditions. A bending moment that bends a beam convex downward (tensile stress on bottom fiber) is considered positive, while convex upward (compressive on bottom fiber) is negative. Figure 1: Coordinate system of a beam. Moment and shear diagram...

Figure 1: A bolted joint works like a stiff spring. Tightening the nut stretches the bolt (tension) and compresses the parts (clamping force). 1. Bolt Selection for Required Clamping Force The primary goal of a bolted joint is to provide a required clamping force (F) between mechanical components to prevent separation or sliding. If a set of n bolts is used, and the total load is distributed equally, the required clamping load per bolt is: P = F / n Advertisement Defining Material Limits (Proof Strength) Bolts are selected from standard grades (e.g., SAE J429 Grade 5 or 8, ASTM A325). Instead of designing to the yield strength, bolt design uses Proof Strength (σ) . Engineering Insight: Proof vs. Yield Proof strength is slightly lower than yield strength. It is the maximum tensile stress a bolt can withstand without experiencing any permanent set. Designing to proof strength ensures the bolt remains entirely elas...