Experimental and numerical study of auxetic sandwich panels on 160 grams of PE4 blast loading

Mines, specifically as Anti-Tank (AT) mines are a significant threat for defence vehicles. While approaches such as v-shaped hulls are currently used to deflect the blast products from such threats, such a solution is not always usable when hull standoff is limited. As such the development of a low profile, energy absorbing solution is desirable. One approach that has potential to achieve these requirements are sandwich panels. While sandwich panel cores can be constructed from various materials, one material of particular interest are auxetics. Auxetic are materials that exhibit a negative Poisson’s ratio. This material has potential to be an efficient an impact energy absorber by increasing stiffness at local deformation by gathering mass at the impact location. This study investigates the effectiveness of novel auxetic core infills alongside three other panel types (monolithic, air gap, polymer foam sandwich) against buried charges. 160 grams of PE4 were buried in 100 mm depth and 500 mm stand off the target. Laser and High Speed Video (HSV) system were used to capture the deflection-time profile and load cell sensors were used to record the loading profile received by the panels. Experimental works were compared with numerical model. Explicit model were generated in LSDYNA software as ‘initial impulse mine’ keyword. The result found that the auxetic and foam core panels were effective in reducing peak structural loading and impulse by up to 33% and 34% respectively. Air-filled panels were the most effective to reduce the deflection of the rear of the plate, however variation between capture methods (HSV and Laser system) were reported, while numerical modelling provided comparable plate deflections responses. When normalised against panel weight, the air filled panels were experimentally the most efficient per unit mass system with the auxetics being the least effective

Experimental and computation assessment of thermomechanical effects during auxetic foam fabrication

Auxetic foams continue to interest researchers owing to their unique and enhanced properties. Existing studies attest to the importance of fabrication mechanisms and parameters. However, disparity in thermo-mechanical parameters has left much debate as to which factors dominate fabrication output quality. This paper provides experimental, computational, and statistical insights into the mechanisms that enable auxetic foams to be produced, using key parameters reported within the literature: porosity; heating time; and volumetric compression ratio. To advance the considerations on manufacturing parameter dominance, both study design and scale have been optimised to enable statistical inferences to be drawn. Whilst being unusual for a manufacturing domain, such additional analysis provides more conclusive evidence of auxetic properties and highlights the supremacy of volumetric compression ratio in predicting Poisson’s ratio outcomes in the manufacture process. Furthermore statistical results are exploited to formulate key recommendations for those wishing to maximise/optimise auxetic foam production

Student Experiences With an International Public Health Exchange Project

With growing interconnectivity of healthcare systems worldwide and increased immigration, inappropriate cultural and role assumptions are often seen when cultures clash within a country or when there is practice across country boundaries in times of disaster and during international travel. To increase students' multicultural awareness and work experiences abroad, the authors describe a 7-school, 5-country international student exchange project. The authors also share the students' evaluations of their experiences as they are challenged to erase boundaries and embrace nursing across countries. Participating faculty describe the process, challenges, and keys to success found in creating and living this international project. Students involved in the exchange process evaluate the learning opportunities and challenges and the joy of coming together as newfound colleagues and friends

Revisiting the association between candidal infection and carcinoma, particularly oral squamous cell carcinoma

Background: Tobacco and alcohol are risk factors associated with cancer of the upper aerodigestive tract, but increasingly the role of infection and chronic inflammation is recognized as being significant in cancer development. Bacteria, particularly Helicobacter pylori, and viruses such as members of the human papilloma virus family and hepatitis B and C are strongly implicated as etiological factors in certain cancers. There is less evidence for an association between fungi and cancer, although it has been recognized for many years that white patches on the oral mucosa, which are infected with Candida, have a greater likelihood of undergoing malignant transformation than those that are not infected. Objective: This article reviews the association between the development of oral squamous cell carcinoma in potentially malignant oral lesions with chronic candidal infection and describes mechanisms that may be involved in Candida-associated malignant transformation

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

The preparation and characterisation of auxetic foams for the application of trauma attenuating backings

Blunt body trauma, due to a heavy impact or blow, has the potential to cause catastrophic injury in a broad range of professions and workplace environments. At particular risk are those who work in areas such as the military, the engineering and construction industries, contact sports (such as American football or rugby) or indeed any other area where an individual has the potential to come into physical contact with other moving objects. Unlike other occupations, the primary cause of blunt trauma in the military is associated with high impact kinetic energies transferred onto the body through the deformation and displacement of body armour.To date, the effects of behind armour blunt trauma (BABT) are counteracted by materials known as Trauma Attenuating Backings (TABs), which have the ability to dissipate and redistributed the impact energy. Unlike currently available TABs that utilise conventional materials, this thesis explores the feasibility of reducing the effects of BABT through the employment of auxetic foams. In contrast to conventional materials, auxetics exhibit a negative Poisson’s ratio when subjected to both tensile and compressive loading, whilst also exhibiting a range of enhanced mechanical properties.Utilising the well-established three-step auxetic foam fabrication process, the influence of fabrication parameters with key focus on Poisson’s ratio and energy absorption have been explored. Auxetic foams were produced for a number of fabrication parameter combinations, where heating time and volumetric compression ratio were identified to be codependentin determining Poisson’s ratio and energy absorption behaviour. While many individual samples demonstrated a negative Poisson’s ratio with enhanced energy absorption, due to the presence of defective and/or damaged cellular structures throughout the foam structures, large variability and little sample repeatability were shown to exist between samples produced from the same combination of fabrication parameters.A novel 3D printing approach was then developed to produce two types of repeatable pliable polymeric foam structures (re-entrant and honeycomb, auxetic and conventional, respectively) where the majority of geometric features have a dimensional error between 0.5% - 5.0% and exhibited negative Poisson’s ratios under both tensile and compressive loading.Interestingly under direct impact conditions (7.2J of impact energy under freefall) no discernible difference regarding energy absorption was shown between the auxetic and conventional systems. However, when considered with respect to the peak force, the auxetic systems exhibited a lower overall mean peak force by a factor of two. Whilst the auxetic system significantly reduced the transmitted peak force but maintained similar energy absorption when compared to the conventional system, it was difficult to surmise whether or not the auxetic system performed better than the conventional system. However, with respect to the quasi-static testing (where the auxetics exhibited a greater energy absorption per unit volume due to both systems having an approximately same relative density), for a like-for-like weight basis the auxetic foams absorb more energy than their conventional counterparts due to their structure and not just because of the increase in relative density that the classic auxetic fabrication process instils.Therefore, it may be concluded that auxetics are potentially suitable for the application as a trauma attenuating backing material as they demonstrated that they satisfy the two key requirements that TAB materials must possess: the ability to absorb energy and reduce the transferable force. However, due to a current lack of understanding on the effects governing BABT, particularly in the area of mechanical and biophysical interactions that take place, it is important that more rigorous testing is undertaken to explore other effects, including pressure wave propagation, ergonomics and replicating in-field conditions before committing auxetic foams to a TAB application

Scaled simulation of the blast effects on structures using LEGO blocks: A pilot study

Blast effects on structures is an important topic in this modern age for many practising engineers, including structural engineers designing buildings for safety or weapons engineers attempting to destroy enemy infrastructure. Due to the large costs, time demands, space requirements and expertise required, full scale testing is rarely a feasible approach. As such it is important to be able to effectively model the blast effects on structures. Currently, computer modelling techniques are extensively used, however the results of these models are often difficult to verify, whilst requiring experienced expert users to ensure accurate data