**Related Resources: Design and Engineering General**

### Threaded Fastener Design and Analysis

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Engineering Fundamentals of Threaded Fastener Design and Analysis

Ralph S. Shoberg, P.E.,

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Open: Engineering Fundamentals of Threaded Fastener Design and Analysis

The process of tightening threaded fastener assemblies, especially for critical bolted joints, involves controlling both input torque and angle of turn to achieve the desired result of proper preload of the bolted assembly. Understanding the role of friction in both the underhead and threaded contact zones is the key to defining the relationship between torque, angle, and tension.

There can be as many as 200 or more factors that affect the tension created in a bolt when tightening torque is applied (refer to paragraph 2.2). Fortunately, torque-angle signature curves can be obtained for most bolted joints.

By combining the torque-angle curves with a few simple calculations and a basic understanding of the engineering mechanics of threaded fasteners, you can obtain the practical information needed to evaluate the characteristics of individual fastener tightening processes. The torque-angle curves can also provide the necessary information to properly qualify the capability of tightening tools to properly tighten a given fastener.

TOC

Introduction: Engineering Fundamentals of the Tightening Process

Energy Transfer

Modeling the Tightening Process

Where Does the Torque Go?

Elastic Torque-Tension Relationship

Stress/Strain vs. Torque/Tension

Correlation of Stress-Strain and Turn.7

Force-Deformation and Torque-Angle Diagrams 8

Preload-Preload Efficiency Factor

Torque-Tension Correlation Coefficient

Thread/Underhead Friction Measurements

Automated Tightening Process

Torque-Angle-Tension Control

Introduction

Torque-Angle-Signature

Torque-Angle Signature Analysis

Tightening Curve

Elastic Origin

Loosening Curve

Beyond Yield

Loosening Tendencies

Accurate Measurement

Torque-Angle Signature Analysis Summary

Clamp Force/Strength Considerations

Modeling the Tightening Process

Torque-Tension Coefficient: Nut Factor, K

Experimental Determination of Friction Coefficients8

Thread/Underhead Friction Coefficient Measurements

M-Alpha Diagram

FM-Alpha Diagram

Estimating the Tension-Angle Coefficient

Ultrasonic Stretch

Strain-Gaged Bolt

Force Washer

Model-Calculation: Estimate of Angle-Tension Coefficient

Laboratory Measurement of Friction Coefficients

Material Property-Yield

Torque-Angle Tension Control Summary

Torque-Tension Audits

Introduction

Hand Torque Audit-Tool Torque Capability

Tool Torque Capability/ISO 5393

Release Angle-Tension Audit

Loosening-Embedment or Loss of Preload

Measurements Verify Fastener Torque and Tension

Other Strategies

Torque-Turn-To-Yield2

Prevailing Torque Locknut Signature Analysis 4.3

Hand Torque Tightness Quality Audits

Redefining The Audit

Hand Torque Audit Qualification

Using Torque Angle Records to Determine Joint Stiffness

Material Yield Point

Glossary of Important Terms 8.0

References