How to Prevent Fastener Failure

Fasteners are known as the ‘rice of industry’ and are one of the most widely used basic parts. Glorysteelwork has been working in the fastener field for more than 15 years and has rich product knowledge and practical experience. As an important connection node for load transfer, the reliability of fasteners is closely related to the safe and reliable operation of the whole equipment or structure.

In the process of fastener use, we will inevitably encounter the problem of fastener failure. So, what are the reasons for fastener failure? How should we avoid fastener failure, to extend the service life?

Fastener Application Failure Solutions

There are many reasons for the failure of fasteners, the more common are fracture, slippery teeth, locking, corrosion and so on. After the fastener failure, the light is to affect the subsequent use of the workpiece and fastening again, the heavy is to cause safety accidents, personal safety and property caused by serious losses.

Failure analysis of fasteners is an important way to improve the reliability of products, which helps to improve the design and prevent the recurrence of accidents. This article will be explained from the fastener fracture failure point of view, the failure causes are analysed, so as to provide you with ways to prevent the failure of fasteners.

Below are several situations that can cause fastener failure and preventive measures.

Overloaded

Overload failure of fasteners refers to the failure of external forces exceeding their load-bearing limits, mainly including ductile overload fracture, brittle overload fracture and “debonding”.

Overload failure of bolts usually occurs in the assembly stage, causes overload failure mainly due to.

1. Thread size mismatch, decarburisation or insufficient screwing length resulting in thread debonding.

2. Insufficient material strength, internal defects or cracks and other reasons for insufficient bearing capacity of the bolt and fracture; 3.

3. Due to the unreasonable assembly process, the preload exceeds the normal bearing capacity of the bolt and fracture.

Solution

1. Measure in advance according to the application scenario of the equipment and choose the correct strength, size and length of the bolts.

2. Use higher quality fasteners to reduce factory defects.

3. Reasonable assembly to ensure that the preload force is less than the normal bearing capacity of fasteners.

Hydrogen embrittlement

Hydrogen embrittlement refers to the sudden fracture and failure of a material under a tensile stress lower than the tensile strength, after a gestation period. Hydrogen embrittlement has the typical characteristics of delayed fracture, usually in the fastener assembly pre-tensioning after a few minutes to several months of time suddenly occurred, no signs before the fracture, the harm is greater.

The occurrence of hydrogen embrittlement is mainly related to the hardness of the material, the amount of hydrogen and the tensile stress and other factors. The higher the hardness of the material, the greater the hydrogen content of the matrix, the greater the tensile stress, hydrogen embrittlement is more likely to occur.

Solution

1. In the production process of 12.9 grade and above strength grade fasteners, avoid the use of degreasing, pickling, electroplating, phosphating and other processes.

2. Avoid galvanising products with hardness above 365HV or tensile strength above 1000Mpa.

3. Strict dehydrogenation treatment should be carried out for products with hydrogen embrittlement risk.

Fatigue

Fastener fatigue damage stress is often far below its static load strength limit, belongs to the brittle fracture, and fracture signs are not obvious, is the most common fasteners, the most harmful form of failure.

Thread structure is the fastener fatigue ‘innate factors’. When there are defects in the thread, such as carburisation, decarburisation, processing of sharp corners, streamline cut-off, folding below the middle diameter, etc., its fatigue strength will be reduced. Different bolt structure, its fatigue resistance will also have differences.

Solution

1. Ensure product quality and reduce thread defects during the manufacturing process.

2. Select a thread structure with better fatigue resistance, e.g.: the fatigue performance of ordinary coarse threads is better than that of fine threads; the fatigue performance of rolled threads is better than that of cut threads.

3. Improve the process, for example, using heat treatment and then roll forming process, not only to retain the thread bottom flow line of the dense and integrity, at the same time, can make its resistance to high fatigue performance is significantly better than the heat treatment of the thread before roll forming.

Of course, there may be other influences on fastener failure. To determine the cause of fastener failure, it is necessary to make a specific analysis of the fastener’s use of the environment, materials, structure and so on.