CT of Fuse failure mechanisms

Introduction

Fuses are widely used in electronic systems to protect circuits from damage caused by short circuits or other fault conditions. During a fault, excessive current can flow through the circuit, potentially damaging electronic components. A fuse typically consists of a thin conductive wire enclosed within an insulating protective housing. Understanding the fuse failure mechanism is essential for designing devices that reliably operate and rupture at their specified current rating.

As most fuses are opaque and cannot be disassembled without altering their internal structure, X-ray computed tomography (CT) scanning was used to investigate the failure mode. CT scanning involves acquiring hundreds of X-ray radiographs while the sample is rotated through 360°. These radiographs are then reconstructed into a three-dimensional model for detailed visualisation and analysis.

Experimental

To look inside the fuse, a Nikon XT H 160i CT scanner was used to scan around the fuse using 100kV X-rays, 200uA beam current, 0.25mm copper filter was used to prevent overexposure of the X-ray detector and provides good contrast between elements inside the sample. Due to the systems cone shaped beam the scan geometry was configured to capture the entire fuse within the field of view, resulting in a reconstructed voxel size of 20 μm (38 mm field of view). 

A projection ct view through a fuse showing a blown component

Fig 1: X-ray radiographs of the fuse from side at 90° and 45° from the side view.

Results

The CT data were reconstructed and analysed using Dragonfly 3D World software. AI-based deep learning segmentation was used to separate the fuse into its casing, insulation, and metallic core components. The segmented components were then processed and rendered to improve visualisation and facilitate interpretation of the internal structure.
a 3d segmented model of a blown fuse componentFig 2: AI segmented slice with the fuse and metal casing in orange & insulation material in green.

As shown in Figure 2, the fuse contains two wire elements, one of which has completely failed while the other has partially failed. The radiograph presented in Figure 1 reveals several narrow sections along the fuse element, which are expected to experience higher current density and localised heating. These regions therefore represent the most likely locations for melting and failure initiation. Following failure, molten fuse material was displaced approximately 1.5 mm before being arrested by the surrounding insulation, as shown in Figure 3. The AI-based segmentation was able to identify and separate many of the individual insulation grains. However, because the grains are tightly packed together, the boundaries between adjacent particles were not always clearly defined, leading to some localised inaccuracies. 

a 3d model of a blown fuse component

Fig 3: Segmented fuse with annotated edge to edge distances of the failed component.

Summary 

Computed tomography (CT) is a powerful non-destructive technique for characterising the internal structure of materials and components. Unlike traditional sample preparation methods, CT enables failure modes to be analysed while preserving the original  condition of the specimen. In the case of fuses, CT can be applied to investigate a variety of failure mechanisms under different operating conditions. The ability to rapidly analyse multiple samples provides repeatable Quality control and supports design optimisation.

Acknowledgement  

Melvin Chan