Failure Analysis Process - Part 2: Initial Examination
Written by Matthew Bridson, Metallurgist, IST
Once we receive the spring from our customer, we can start our initial examination stage of the failure analysis.
The first stage is to start big and asses the entire spring. As we progress through the initial examination we focus more on the smaller details. Every spring we receive for a failure analysis is different, and although some may be like ones we have seen in the past, it is imperative we treat each one as unique. We photograph the spring upon its arrival with a high quality DSLR camera. The spring is placed in our light box, it is photographed at many different angles including close up images of the fracture face and surrounding wire surface to ensure we don’t miss anything important. We take extra care in ensuring no further damage is caused to the springs through this stage.
Next up, we use our low power microscope to focus in on the fracture faces and the surrounding wire surface. When we look at the wire surface, we are focusing on the quality and if there are any manufacturing defects, such as coiling marks or evidence of chattering. We also look for any evidence of wear, this informs us that there has been some form of contact. For example, if there is visible coil to coil wear that could insinuates there has been some coil clashing. Signs of external wear could mean that there has been contact with a possible housing, with internal wear showing the potential contact with a mandrel. If a spring has been coated with paint, we are often able to see end coil wear, as the paint has worn against the supports.
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Corrosion is a common sight on fractured springs. When corrosion is a factor, we look for pitting and discolouration. We must be cautious when we see corrosion, as it is common for springs to rust after they have failed, meaning it may not have played any part in the actual failure.
Next, we focus on the fracture face. The first thing we try to understand, is where the initiation region is. There are many factors which can help with this, but the most useful are called beach marks or propagation marks, which appear as arcs emanating from the initiation region.
Even after gaining all this information, we must keep an open mind on how the spring failed, we don’t want to narrow our search too early and potentially miss some important information.
We take numerous images at every stage of the initial examination. We want to have as much evidence as we can before moving forward to the metallurgical work which involves sectioning the spring where information and evidence could be lost.
In our April edition of our The Spring Industry Newsletter we will move on to part 3 and talk about metallurgical analysis and testing.