The effects of 3D printed material properties on shaped charge liner performance

© Cranfield University, 2019Shaped charges operate by explosively loading a (typically metallic) liner to produce a jet travelling at extremely high velocity (9-12 km/s). Such explosive loading involves highly non-linear transient phenomena. As such, a very wide range of physical processes must be considered to enable accurate characterisation of such events – with material behaviour within these (pressure / strain-rate) regimes providing insight into problems ranging from shaped charge performance itself through to formation of new material phases at high pressures. Unlike other high strain impact events, the shaped charge phenomenon results in hydrodynamic material flow of the liner which is an integral aspect of the shaped charge design. As such, the study of shaped charge liners has been the subject of numerous scientific research studies for over 50 years since its discovery. When explosively loaded, the liner is stretched extensively during their elongation to form a jet. The jet length depends on the ductility of the liner material, and this is strongly linked to the microscopic crystal structure, which depends on the original material properties and the processes used to produce the liners. There are several processes currently used for liner production. This thesis outlines the different liner production techniques, their advantages/disadvantages and explores the potential of employing additive manufacturing (3D printing) technique for shaped charge liner production. As 3D printed parts are being considered as a possible replacement for conventionally processed parts, this PhD work fits into this long-term vision; with built parts compared in density and mechanical strength to their bulk material equivalents. More so, 3D printing is shown to present some potential benefits for the production of efficient liners including high precision, cost-effectiveness and the potential to realise customized geometries. The use of fine powders may also allow alternative microstructures to be produced with potentially interesting results. This element of the study forms the first part of this thesis, aimed at investigating the mechanism elucidating the performance of 3D printed liners processed through direct metal laser sintering process (selective laser sintering) and filament deposition modelling processes (Polylactic Acid). The next part of this work provided additional insights on the additive manufactured processed employed through investigation of the dynamic behaviour of polylactic acid, employed in the filament deposition modelling process and static (optical and scanning micrographs) observation of the laser sintered liners in their as - manufactured and deformed state, in comparison with traditional machined liners. Autodyn 2D numerical hydrocode was employed to understand how temperature influences the deformation pattern (grain refinement); providing new insights on liner deformation. Finally, a novel computational technique to determine the Virtual Origin of shaped charges was developed to provide a ready route to predict more accurate SC performance

Comparison of the microstructure of machined and laser sintered shaped charge liner in the hydrodynamic regime

To gain further insight into the mechanisms underlying jet formation and elongation of laser sintered shaped charge liners under high strain rate deformation, Cu–Cr–Zr alloy liners fabricated by selective laser sintering process were deformed by explosive detonation. Their as-manufactured (liner) and resultant (slug) microstructure have been investigated in comparison with those of traditional machined liners employing both optical and scanning electron microscopy. The resultant slug microstructure of both machined and laser sintered liners revealed a smaller refined equiaxed grain size consistent with traditionally fabricated liners, characteristic of dynamic recrystallization. The disappearance of the (originally present) pores in the post-shot/recovered material microstructure was observed for laser-sintered liners. Comparison of the forward and rear region of the slug revealed variations in liner deformation, a result attributed to temperature variation across the slug. In contrast with the machined liner, a unique feature of precipitation, observed in the ending (slug) microstructure of the laser sintered liner is indicative of the associated extreme high strain and strain rate liner deformation which occurred during slug formation. The precipitates are likely compounds of Chromium and Zirconium which are constituents of the laser sintered copper alloy—the first time this observation is reported. This study provides a link between post charge evolution microstructure and liner manufacturing processes, potentially providing a new route to help optimise jet formation and effectiveness

The dynamic response of dense 3 dimensionally printed polylactic acid

Polylactic acid (PLA) is commonly used as a feedstock material for commercial 3D printing. As components manufactured from such material become more commonplace, it is inevitable that some of the resultant systems will be exposed to high strain-rate/impact events during their design-life (for example, components being dropped or even involved in a high-speed crash). To this end, understanding the shock properties of polylactic acid, in its role as a major raw material for 3D printed components, is of particular importance. In this work, printed samples of PLA were deformed by one-dimensional shock waves generated via the plate impact technique, allowing determination of both the Hugoniot Equation of State (EOS) and shear strength of the material. Both linear and non-linear EOS forms were considered in the US-Up plane, with the best-fit found to take the general form US=1.28+3.06−1.09Up2" role="presentation" style="display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border-width: 0px; border-style: initial; position: relative;">US=1.28+3.06−1.09U2pUS=1.28+3.06−1.09Up2 in the Us−Up" role="presentation" style="display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border-width: 0px; border-style: initial; position: relative;">Us−UpUs−Up plane, consistent with other polymers. Use of lateral Manganin gauges embedded in the material flow allowed consideration of lateral stress evolution at impact pressures ranging from 0.3 to 4.0 GPa. Shear strength was observed to increase with impact stress, however, with minimal strengthening behind the shock front. Deviation of the measured stress from the predicted elastic measurement (corresponding to the PLA’s Hugoniot Elastic Limit) was observed at longitudinal stress of 0.90 ± 0.05 GPa, within range of polymeric materials of similar characteristics—the first time this important parameter has been measured for PLA. As a result, this material characterisation will allow numerical modellers to accurately predict the structural response of PLA-based components/structures against high strain rates such as impacts or drops

Epidemiology of lumbar disc herniations in adults with low back pain in Enugu, Nigeria

Background: Lumbar intervertebral disc herniation is used to describe a spectrum of anatomical abnormalities involving disc extension beyond the interspace. It follows a tear in the annulus fibrosus of the intervertebral disc. It is one of the most common causes of low back pain among adults. The study aims to assess the epidemiological pattern of lumbar disc herniations among adults with low back pain in Enugu urban.Methods: The study was a prospective study at National Orthopedic Hospital Enugu and Annunciation Specialist Hospital Enugu. Following ethical approval and written informed consent, patients who met the inclusion criteria were consecutively recruited. The MRI scans of the participants were viewed using DICOM® (Digital Imaging and Communications in Medicine) software on laptop computer. The data included the patients’ demographics, functional disability index for back pain, weight, height, the anatomical level(s) and site(s) of the herniated disc among other parameters.Results: A total of 81 subjects who met the inclusion criteria were included and analyzed using SPSS version 20.0. The mean age of the subjects is 52.99±13.13 years. The most common affected age group is 51-60 years (27.2%). Majority of the subjects (68; 84%) had multiple level herniations which usually includes L4 level(74; 91.4%).Conclusions: That multilevel lumbar disc herniation is far more common than single level herniation with a prevalence of 84% among adults with low back pain in Enugu urban. That, there is statistically significant association of lumbar disc herniation and increasing age

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely