Reference object for evaluating the accuracy of porosity measurements by X-ray computed tomography

Abstract Internal defects such as voids and porosity directly influence mechanical properties, durability, service life and other characteristics of industrial parts. There are several non-destructive and destructive methods for defects detection and evaluation. Recently, X-ray Computed Tomography (CT) has emerged as an effective tool for geometrical characterization of internal defects. 3D information about internal voids/porosity extracted from CT datasets can be utilized in many applications, such as production processes optimization and quality control. However, there are still challenges in using CT as a traceable method for internal voids dimensional measurements. In order to enhance the accuracy and reliability of CT porosity measurements, a metrological validation method is required. This study presents the application of a new reference object for accuracy evaluation of CT porosity measurements and discusses results obtained by using it. The reference object is made of aluminium and is composed of a cylindrical body and four cylindrical inserts with micro-milled hemispherical features of calibrated sizes resembling artificial flaws. The accuracy of porosity measurements is evaluated according to various characteristics (diameters and depths measurements errors) and repeatability of measurements. Design of experiments technique is used to investigate the influence of CT parameters settings on porosity measurement accuracy

x ray computed tomography for metal additive manufacturing challenges and solutions for accuracy enhancement

Abstract Additively manufactured parts are characterized by metrological challenges and complexities, due to several reasons, including the inherent presence of internal defects and complex surface topography. Micro X-ray computed tomography is currently used to perform dimensional evaluations, porosity analysis and, more recently, surface topography measurements of additively manufactured parts thanks to the possibility of analysing non-destructively also non-accessible geometries and micro-scale features. However, the accuracy of these evaluations can be limited due to the high complexity of such parts. This work summarizes the results of experimental investigations on metrological challenges and accuracy of tomographic analyses, based on studies performed on Ti6Al4V specimens produced via selective laser melting

Porosity testing methods for the quality assessment of selective laser melted parts

This study focuses on the comparison of porosity testing methods for the quality assessment of selective laser melted parts. Porosity is regarded as important quality indicator in metal additive manufacturing. Various destructive and non-destructive testing methods are compared, ranging from global to local observation techniques and from quick low-cost to expensive time-consuming analyses. Forty test specimens were produced using five varying control factors. The experimental results show that Archimedes and CT methods compare well, Archimedes can be deployed to inspect parts in small series and CT pre- and post-cut analysis show that post-cut porosity results are systematically higher

Pore-Scale Transport and Two-Phase Fluid Structures in Fibrous Porous Layers: Application to Fuel Cells and Beyond

We present pore-scale simulations of two-phase flows in a reconstructed fibrous porous layer. The three dimensional microstructure of the material, a fuel cell gas diffusion layer, is acquired via X-ray computed tomography and used as input for lattice Boltzmann simulations. We perform a quantitative analysis of the multiphase pore-scale dynamics and we identify the dominant fluid structures governing mass transport. The results show the existence of three different regimes of transport: a fast inertial dynamics at short times, characterised by a compact uniform front, a viscous-capillary regime at intermediate times, where liquid is transported along a gradually increasing number of preferential flow paths of the size of one-two pores, and a third regime at longer times, where liquid, after having reached the outlet, is exclusively flowing along such flow paths and the two-phase fluid structures are stabilised. We observe that the fibrous layer presents significant variations in its microscopic morphology, which have an important effect on the pore invasion dynamics, and counteract the stabilising viscous force. Liquid transport is indeed affected by the presence of microstructure-induced capillary pressures acting adversely to the flow, leading to capillary fingering transport mechanism and unstable front displacement, even in the absence of hydrophobic treatments of the porous material. We propose a macroscopic model based on an effective contact angle that mimics the effects of the such a dynamic capillary pressure. Finally, we underline the significance of the results for the optimal design of face masks in an effort to mitigate the current COVID-19 pandemic

Pore-Scale Transport and Two-Phase Fluid Structures in Fibrous Porous Layers: Application to Fuel Cells and Beyond

We present pore-scale simulations of two-phase flows in a reconstructed fibrous porous layer. The three-dimensional microstructure of the material, a fuel cell gas diffusion layer, is acquired via X-ray computed tomography and used as input for lattice Boltzmann simulations. We perform a quantitative analysis of the multiphase pore-scale dynamics, and we identify the dominant fluid structures governing mass transport. The results show the existence of three different regimes of transport: a fast inertial dynamics at short times, characterised by a compact uniform front, a viscous-capillary regime at intermediate times, where liquid is transported along a gradually increasing number of preferential flow paths of the size of one–two pores, and a third regime at longer times, where liquid, after having reached the outlet, is exclusively flowing along such flow paths and the two-phase fluid structures are stabilised. We observe that the fibrous layer presents significant variations in its microscopic morphology, which have an important effect on the pore invasion dynamics, and counteract the stabilising viscous force. Liquid transport is indeed affected by the presence of microstructure-induced capillary pressures acting adversely to the flow, leading to capillary fingering transport mechanism and unstable front displacement, even in the absence of hydrophobic treatments of the porous material. We propose a macroscopic model based on an effective contact angle that mimics the effects of the such a dynamic capillary pressure. Finally, we underline the significance of the results for the optimal design of face masks in an effort to mitigate the current COVID-19 pandemic

quality and productivity considerations for laser cutting of lifepo4 and linimncoo2 battery electrodes

Abstract Laser cutting of lithium-ion battery electrodes has been shown to be a viable alternative to mechanical blanking for some specific electrode types, yielding similar cut quality and throughput but with decreased on-going costs due to lower maintenance requirements. The multitude of electrode chemistries within the lithium-ion classification, particularly with regards to the cathode, together with the sensitive nature of battery components such as the polymeric separator films and electrodes themselves, requires careful assessment of defects for each electrode type. In the present work, cutting of LiNiMnCoO2 (LNMC) coated aluminium cathodes and graphite coated copper anodes is performed at 100 mm/s with a 1064 nm pulsed fibre laser with 25 μm spot size, varying the pulse duration, energy and repetition rate over the ranges 4-200 ns, 8-935 μJ and 20-500 kHz, respectively. Process productivity is assessed in terms of the minimum cutting power at which complete electrode penetration takes place. A scanning electron microscope is utilised to assess upper coating layer clearance width and to determine the presence and dimensions of defects resulting from melting of the coating layers. Results are compared with previous cuts performed on LiFePO4 (LFP), with differences observed in the parameters leading to minimum average cutting power and optimum quality between cathode types. Laser pulse fluence in the range 35-40 J/cm2 with 30 ns pulse duration and 100 kHz repetition rate is found to lead to the highest cutting efficiency and quality for the LFP cathode, while 110-150 J/cm2 fluence with 200 ns pulse duration and 20 kHz repetition rate is instead found to be ideal for the LNMC cathode and for the anode. The present on-going study indicates relatively strong sensitivities to electrode composition and laser pulse fluence for cutting efficiency and quality

Qualification and testing of CT systems

This chapter focuses on system verification and conformance to specifications. System qualification is carried out to ensure that the system and its components achieve the best performance-usually corresponding to the specifications made by the manufacturer. Acceptance and reverification testing are undertaken on the overall integrated system to check whether the system performs as specified