Bullfrog: Enabling High-Rate Low-Waste Composite Manufacturing
Bullfrog Technologies has sat with the question:
Why does composite manufacturing lose so many parts to defects that could have been caught earlier?
Earlier this year, Dr Christopher Sutcu from the University of Southampton published a paper as part of their work package with us. It is a thorough review of Active Thermography for composite NDT, covering the science of defect detection, the full landscape of thermographic techniques, and critically, a rigorous validation of whether lower-cost uncooled camera systems can genuinely match the performance of expensive cooled photon detectors when paired with the right signal processing.
The short answer: they can. And that finding is central to what makes Bullfrog viable as a shop-floor tool rather than a laboratory instrument.
Below is the executive summary and introduction to the paper. We urge you to go deeper and explore the work done on the signal processing comparisons, the full experimental literature review, and the conclusions on excitation parameter optimisation. The full paper is linked at the end.
Excerpt: Bullfrog: Enabling High-Rate Low-Waste Composite Manufacturing
Executive Summary
Project Bullfrog aims to enable high-rate, low waste production of advanced composite structures by utilising Active Thermography (AT) to produce a low cost, Non-Destructive Testing (NDT) system. This will enable understanding of manufacturing defects via in-situ testing. The primary breakthrough is the use of lower cost uncooled (i.e. microbolometer) thermal imaging cameras and robust signal processing pipelines to remove the reliance on more expensive and operationally complicated cooled photon detector cameras to both qualitatively and quantitatively detect common manufacturing defects seen in composite materials.
A brief overview of composite materials and the most common manufacturing and in service damage types are presented, as well as how they impact residual strength of composite materials. This document delivers the state of the art in terms of pulsed thermographic experimental practises and why AT is positioned as the optimal NDT solution for high-rate composite material inspection compared to other NDT techniques. A comparison and validation of the industrial use case of using uncooled vs cooled camera systems is examined and commonly used signal processing methods in relation to Pulsed Thermography (PT) are documented.
The technical and economic feasibility of using uncooled microbolometers for industrial composite NDT is validated by numerous studies demonstrating that, when paired with robust signal processing, these systems deliver performance comparable to cooled counterparts. Future work for Project Bullfrog will focus on the optimisation of experimental excitation parameters (standoff distance, power delivery, and pulse length), which seem to vary considerably in the scientific literature depending on specimen material, geometry and defect types. Generalising these parameters remains the biggest challenge in producing a robust NDT system.
Introduction
Non-Destructive Testing & Evaluation (NDT & E) techniques are extremely valuable methods for analysing the structural health of engineering structures without cutting apart or altering the material. Therefore, their non-invasive nature allows for characterisation of the structure while it is still in service, minimising operational downtime and eliminating the costs associated with sampling structural components. Additionally, NDT & E serves as a robust predictive tool as it can effectively identify a wide range of structural defects, from manufacturing of the component until the end of its operational life. This approach provides a wealth of information about how design choices can influence the lifetime of the structure and fundamentally, how damage propagates in engineering structures [1].
The understanding of damage propagation becomes even more relevant in the area of composite materials, due to their inherent anisotropic structure. Composite materials are composed materials made up of two or more constituent materials, which combine to form a material that is superior to its individual components. Composite materials have seen wide success in aerospace, automotive and maritime industries in recent years due to their superior specific strength compared to more dense metallic materials [2]. This, however, comes at a cost, as the damage accumulation is non-trivial; hence the growing important partnership between composite materials and NDT & E techniques.
NDT & E technology has steadily matured over the last couple of decades and now encompasses a wide range of techniques all with differing qualitative and quantitative abilities. A non-exhaustive list of NDT & E techniques used today are visual inspection, ultrasonic testing, liquid penetrant testing, radiography and holography [3]. Among the NDT & E techniques, there is also Active Thermography (AT). AT is rapidly growing in science and engineering due to the promising properties it has over other NDT & E techniques. Specifically, its non-contact and non-invasive nature allows for highly efficient data acquisition and simplified experimental setups compared to methods requiring physical coupling or intrusive access. This can potentially allow for easier generalisation of the experimental set-up for a diverse range of materials and geometries, proving highly advantageous for the development of a robust NDT & E system.
The full paper covers a great deal, including a detailed breakdown of pulsed, lock-in, and frequency modulated thermographic techniques, a comparison of cooled vs uncooled camera systems across a wide range of experimental conditions, and a comprehensive table of signal processing methods and their trade-offs.
If you work in composites manufacturing, NDT, or aerospace quality engineering, it's worth reading in full.
Read the full paper here:
