A stylized illustration of a loosening bolt on a futuristic bridge, symbolizing engineering challenges and the importance of joint reliability.

Bolted Joint Blues? How to Prevent Self-Loosening and Keep Your Structures Secure

Nico Varela in Tech & Innovation September 2025 • 4 min read.

"A Deep Dive into Dynamic Shear Loads and Innovative Solutions for Bolted Joint Reliability"

Bolted joints are the unsung heroes of countless engineering structures, offering a blend of simplicity, cost-effectiveness, and ease of assembly. From bridges to automobiles, these connections are fundamental to modern infrastructure and technology. However, they are not without their vulnerabilities. One persistent issue is self-loosening—the gradual untightening of bolted joints under time-varying loads.

Self-loosening is more than just a minor inconvenience; it’s a potential safety hazard that can lead to catastrophic failures. Imagine a critical joint in an aircraft wing slowly coming undone mid-flight, or a bridge support gradually weakening under the constant stress of traffic. The consequences can be severe, making the study of loosening mechanisms and influencing factors a crucial area of research.

Recent research published in the International Journal of Modern Physics B delves into the self-loosening behavior of bolted joints subjected to dynamic shear loads. This study, conducted by Junbo Zhou, Jianhua Liu, and their team, explores how initial tightening torque, shear load amplitude, and bolt material impact the stability of these essential connections. Understanding these factors is key to developing strategies that mitigate self-loosening and enhance the reliability of bolted joints.

Why Do Bolted Joints Loosen? Understanding Dynamic Shear Load

A stylized illustration of a loosening bolt on a futuristic bridge, symbolizing engineering challenges and the importance of joint reliability.

Dynamic shear load is the primary culprit behind self-loosening. Unlike static loads, which remain constant over time, dynamic loads fluctuate, causing the bolted joint to experience varying stresses. This constant change in stress can lead to several detrimental effects:

Relative Slip: The most significant cause of self-loosening is the relative slip between contacting threads and the bearing surface of the bolt or nut. As the load changes, these surfaces slide against each other, gradually reducing the clamping force.

Plastic Deformation: Under high dynamic loads, the materials of the bolt and joint can undergo plastic deformation. This means they permanently change shape, leading to a loss of preload (the initial tension in the bolt).
Fretting Wear: The small, repetitive movements between the contacting surfaces cause fretting wear. This wear removes material, further reducing the clamping force and accelerating the loosening process.

The study highlights that the loosening process typically occurs in distinct stages. Initially, the clamping force remains relatively stable. However, as the dynamic load continues, plastic deformation and relative rotation between the bolt and nut cause the clamping force to drop rapidly. Over time, this leads to a gradual decline in the clamping force until the joint is significantly loosened.

Securing the Future: Practical Steps to Enhance Bolted Joint Reliability

Self-loosening in bolted joints is a complex issue, but with the right knowledge and strategies, it can be effectively mitigated. Understanding the critical factors identified in recent research—such as initial tightening torque, shear load amplitude, and material selection—is the first step. By applying these insights, engineers and designers can create more reliable and safer structures, ensuring that the unsung heroes of modern engineering continue to perform their vital role without fail.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1142/s0217979219400095, Alternate LINK

Title: Self-Loosening Behavior Of Bolted Joints Subjected To Dynamic Shear Load

Subject: Condensed Matter Physics

Journal: International Journal of Modern Physics B

Publisher: World Scientific Pub Co Pte Lt

Authors: Junbo Zhou, Jianhua Liu, Huajiang Ouyang, Zhenbing Cai, Jinfang Peng, Minhao Zhu

Published: 2019-01-30

Everything You Need To Know

What is self-loosening in bolted joints, and why is it a significant concern in engineering structures?

Self-loosening in bolted joints is the gradual untightening of these connections under time-varying loads, making it a significant issue because it can lead to catastrophic failures in critical structures. For example, the consequences could be severe if a joint in an aircraft wing comes undone mid-flight or a bridge support weakens under traffic. It's more than a minor inconvenience; it’s a potential safety hazard that requires thorough understanding and mitigation.

What is dynamic shear load, and how does it contribute to the self-loosening of bolted joints?

Dynamic shear load is the primary cause. Unlike static loads, dynamic shear loads fluctuate, causing the bolted joint to experience varying stresses that lead to relative slip between contacting threads and the bearing surface of the bolt or nut, plastic deformation in the materials of the bolt and joint, and fretting wear between the contacting surfaces. This constant change reduces the clamping force and accelerates the loosening process.

Can you describe the stages of the self-loosening process in bolted joints under dynamic shear loads?

The loosening process typically occurs in stages. Initially, the clamping force remains relatively stable. However, as dynamic load continues, plastic deformation and relative rotation between the bolt and nut cause the clamping force to drop rapidly. Over time, this leads to a gradual decline until the joint is significantly loosened. Junbo Zhou, Jianhua Liu, and their team found that initial tightening torque, shear load amplitude, and bolt material all affect the stability of the joints.

Can self-loosening in bolted joints be effectively mitigated, and what are the initial steps to take?

Yes, understanding the critical factors identified in recent research—such as initial tightening torque, shear load amplitude, and material selection—is the first step. By applying these insights, engineers and designers can create more reliable and safer structures, ensuring that the bolted joints perform their vital role without fail. Using insights like those in the International Journal of Modern Physics B study can help reduce failures.

What specific factors are critical in preventing self-loosening of bolted joints, and how do they influence the joint's reliability?

Several factors are studied to prevent bolted joint failures, including initial tightening torque, shear load amplitude, and bolt material. Initial tightening torque affects the initial clamping force, shear load amplitude determines the magnitude of stress experienced by the joint, and bolt material influences the joint's resistance to plastic deformation and wear. Managing these factors can enhance the reliability and longevity of bolted joints in various applications.