Modelação numérica da resposta dinâmica de proteções multi-material sujeitas a impactos balísticos

With the current events concerning terrorist attacks, it is imperative to perform research and development on issues related to ballistic protection. The need to protect soldiers from high impact velocity threats has become increasingly important and challenging. Within the scope of this work the aim is to develop an optimised armour configuration for an advanced ballistic helmet design, which is able to defeat impacts from high velocity rifle bullets. This is done using finite element modelling supported by results from experimental tests. The design presented here is based on four different layers, where: (i) the first layer is designed to break and erode the projectile, (ii) the second layer absorbs the kinetic energy of the projectile, (iii) the third layer minimises the back face deflection and, finally, (iv) a fourth layer absorbs the shock wave of the initial impact and provides the necessary standoff (required by the back face deflection) for the first three layers, so that direct contact between these layers and the head does not occur. The results obtained by simulation with the finite element method (using LS-DynaTM) demonstrate that the models agree with the experimental results. A detailed numerical study of the diferent layers as well as the 7.62x39 M43 projectile was made. A good correlation between numerical and experimental results of the ammunition and armour materials was achieved, as well as between numerical and experimental results in terms of the depth of indentation as a function of impact velocity of the new ballistic helmet design. The last two sets of numerical analysis made for the helmet shell configuration was relative to the shock absorbing layer. The first set of simulations consisted of introducing rigid boundaries to the composite layer of the at panel. A second set of simulations considered the composite layer of the at panel to be attached to a rigid frame, without fixing this frame. From the simulation results, a shock-absorbing layer can be designed in such a way as to significantly reduce the risk on behind-helmet blunt trauma, and with acceptable force transfer to the head. An optimum standoff distance was determined for a ballistic helmet concept able to stop the M43 Kalashnikov projectile.Face aos sucessivos eventos relativos a ataques terroristas, é imperativo realizar investigação científica e desenvolvimento em questões relacionadas com a proteção balística. O objetivo principal do trabalho que aqui se apresenta _e desenvolver um novo capacete balístico capaz de parar projéteis de alta velocidade, usando modelos de elementos finitos, validados com base em resultados de testes experimentais. O modelo de capacete aqui apresentado _e composto por quatro diferentes camadas, onde: (i) a primeira é capaz de deformar e fraturar o projétil, especialmente o núcleo de aço, ajudando a reduzir a sua velocidade; (ii) a segunda camada absorve energia cinética do projétil, (iii) a terceira limita a deflexão da face anterior e, finalmente, (iv) a quarta camada absorve a onda de choque do impacto inicial e garante a distância necessária para evitar o contato dessas camadas com a cabeça. Foi também realizado um estudo numérico detalhado das diferentes partes do projétil 7.62 x 39 M43. Obteve-se uma boa correlação entre os resultados numéricos (usando o software LS-DynaTM) e experimentais para os modelos do projétil quer do equipamento de proteção pessoal (capacete). Atingiu-se também uma boa correlação em termos de velocidade de impacto em função da profundidade de deformação do novo desenho de capacete balístico. Realizou-se uma análise numérica mais detalhada para a configuração do capacete relativa _a camada de absorção da onda de choque. Um primeiro conjunto de simulações consistiu em introduzir limites rígidos nas extremidades das três primeiras camadas. Um segundo conjunto de simulações considerou as três primeiras camadas anexadas a uma estrutura rígida, fixa no capacete. A partir dos resultados numéricos, conclui-se ser possível projetar uma camada de absorção da onda de choque de maneira a reduzir significativamente o risco de traumatismo craniano causado pelo impacto no capacete. Uma distância mínima entre a cabeça e o capacete pode, portanto, ser determinada para um novo modelo de capacete balístico capaz de parar o projétil M43 Kalashnikov.Programa Doutoral em Engenharia Mecânic

Dinamičko mehanička svojstva hibridnih nanokompozitnih materijala

Predmet istraživanja ove doktorske disertacije pripada oblasti nanomateijala i nanotehnogija koja je u trendu savremenih istraživanja. Posebno su intenzivna istraživanja u oblasti polimernih nanokompozita gde tradicionalno slabe strane polimera (niske vrednosti parametara mehaničke čvrstoće i loša termostabilnost) se značajno poboljšavaju primenom malog udela nano punioca i ojačanja uz neznatan porast gustine. Razvijena je metoda dizajniranja strukture nanokompozitnih balističkih materijala sa gledišta poboljšanja njihovih svojstava otpornosti pri udarima visoke energije. Proučeni su uslovi dobijanja laminarnih kompozitnih materijala p-aramid/poli (vinil butiral). Poli (vinil butiralni) sloj nanošen je u obliku disperzije poli (vinil butirala) i nano čestica SiOR2R u etil-alkoholu, pri čemu su korišćene modifikovane i nemodifikovane čestice SiOR2 Rsa vezujućim agensom-AMEO silanom. Na taj nači je utvrđen veliki značaj modifikacije nano čestica SiOR2R sa silanima na mehanička, termička i antibalistička svojstva dobijenih hibridnih nanokompozitnih materijala. Savremena istraživanja u ovoj oblasti usmerena su u pronalaženju mehanizama zaustavljanja rasta prsline modifikovanjem strukture na nano nivou što je i predmet ove doktorske disertacije. Proučavanja u okviru ove disertacije bila su usmerena na istraživanja mehanizama apsorpcije energije u nanokompozitima pri udarnim opterećenjima visoke energije i ponašanje nano čestica kao konstituenata u strukturi hibridnih kompozitnih materijala. Sinteza ovih nanokompozitnih materijala izvršiće se primenom koloidnih suspenzija koje se karakterišu ekstremnim porastom viskoznosti pri velikim brzinama smicanja kojima su izloženi pri udarnim naprezanjima. Originalnost ideje se ogleda što je princip hibridizacije primenjen na izradu laminatnih balističkih ploča sa laminama koje su različito nanomodifikovane a samim tim i sa različitim svojstvima. Značaj ove ideje je što različito nanomodifikovane lamine omogućavaju izradu funkcionalno gradijentnih kompozitnih materijla od nano do mikro nivoa. Ciljevi ove disertacije su višestruki: 1) proučavanje mehanizama procesiranja nano prahova različitih oksida u različitim disperzionim sredstvima prema klasičnim metodama i savremenim metodama modifikovanja površine čestica; 2) eksperimentalna istraživanje uticaja procesnih uslova brizganja i toplog presovanja hibridnih nonokompozita sa tkaninama od aramidnih vlakana sa različitim udelom modifikovanih nanočestica na njihova dinamickomehanička svojstva (modul sačuvane i izgubljene energije i tangens gubitaka) u različitom temperaturnom intervalu pri različitim frekvencijama); 3) eksperimentalna istraživanje uticaja procesnih uslova brizganja i toplog presovanja hibridnih laminatnih nonokompozita sa matricom od poli (vinil butirala) sa razlicitim udelom modifikovanih cestica silicijum dioksida na makromehanicka svojstva (Jungov modul elasticnosti, zatezna cvrstoca, prekidno izduženje); 4) eksperimentalna ispitivanja otpornosti na razaranje dobijenih hibridnih nanokompozitnih materijala na udar velikim energijama i brzinama (standardna balisticka ispitivanja sa municijom u realnim uslovima).The purpose of this dissertation is to investigate the effects of lamination and hybrid soft armor systems through ballistic impact. The investigation was carried out by using dynamic mechanical analysis and actual ballistic testing. The most important conclusions derived from this research are that lamination of the systems with very low resin content are superior to multiple non-laminated systems, and this advance could be improved further by hybrid systems using nanomodified fabric layers on the impact side and relatively tighter woven fabrics between the layers. This dissertation reports the preparation of SiOR2R and TiOR2R/poly (vinyl butyral) nanocomposites with enhanced dynamic mechanical properties. Silica and titania nanoparticles were introduced in the matrix as the neat powder and as colloidal sol using the melt mixing process. Composites reinforced with colloidal sol silica and titania showed higher mechanical properties than the ones reinforced with as-received particles. When sol TiOR2R particles are used, the highest increase of storage modulus of about 54% is obtained for 5 wt% loading, while for sol SiOR2R, the storage modulus increases with the addition of nanosilica with the largest increase of about 99% for 7 wt% loading. In addition, nanocomposites were introduced within Kevlar/PVB composites. The addition of 5 wt% silica and titania colloidal sol lead to the remarkable increase of the storage modulus for about 98 and 65%, respectively. Largest contribution of nanoreinforcements in lowering the glass transition temperature is observed for 7 wt% loading of TiOR2R and SiOR2R colloidal sol. This study reports the manufacture of new fabric forms from the preparation of hybrid laminated multi-axial composites with enhanced thermo-mechanical properties. Thermal and dynamic mechanical analysis of polymer matrix films and fabricated hybrid composites were employed in order to determine the optimal material composition and reinforcement content for composites with improved viscoelastic properties. The introduction of 5 wt. % silica nanoparticles in a composite of p-aramid– poly(vinyl butyral) led to significant improvements in the mechanical properties, and the addition of silane coupling agents yielded maximal values of the storage modulus for hybrid nanocomposites. The introduction of silane led to a better dispersion and deagglomeration of SiOR2R particles and to the formation of chemical bonds between organic and inorganic constituents, or p-aramid–poly(vinyl butyral) composites. In this way, the mobility of macromolecules was reduced, which can be seen from the decreasing value of damping factor for the p-aramid–poly(vinyl butyral) composite. Analysis of the glass transition temperature of the composite with amino-functionalized silica nanoparticles revealed improved thermal stability in addition to the aforementioned mechanical properties of the tested materials

Investigation into energy dissipation in equal channel angular extrusion

The field of energy absorption is definitely one the most important in engineering design, as many types of static and dynamic structures, designed and built for different purposes and tasks, require energy absorption capabilities under loading conditions. This thesis is aimed at the introducing experimental and theoretical analyses of a novel and revolutionary technique to dissipate unwanted energy in engineering systems. An extensive literature review on existing energy absorbers was undertaken in relevant application fields such as structural and personal protection. Hence, devices attached to buildings and designed to dissipate energy due to severe earthquakes have been discussed and compared. Types considered, in this review, are mainly based on friction, viscoelasticity and material yielding mechanisms. Furthermore, methodologies to strengthen structures against impacts such as those used in armoured walls are described, and their capabilities assessed. In addition techniques to protect the human body against dangerous loads were reviewed, and important issues for chest and head protection, leg defences in football and safety in motorcycles have been investigated. Experimental results about energy absorption in crash tests have been studied. Also, as an example the use of current technologies to dissipate energy during landing operations in aircrafts have been considered. A classified chart of energy absorption devices in different applications has been produced and referenced. In general most energy absorption devices were shown to be capable to eventually dissipate dangerous and unwanted energy, but poor reusability and predictability after impact were not part of the design process. The research base in this thesis is a novel energy dissipation technique capable of designing Universal Reusable Energy Absorption Devices (UREAD). This technique exploits the principles and working mechanisms that are used in extrusion of deformable materials through intersecting channels. Such mechanism of deformation is known in literature as Equal Channel Angular Extrusion (ECAE). ECAE is one of the severe plastic deformation processes. A theoretical analysis of internal pressure and stresses developed at the interface with the tools has been presented for channels of different geometrical parameters. In addition, energy absorption capabilities have been analysed by the Upper Bound ii method. Also, a numerical solution based on the implementation of the Finite Element Analysis, in ANSYS commercial package was obtained to show the intensity of stress distribution in the deforming material and the tools surrounding it. UREAD devices of different dimensions and geometries were designed, manufactured and tested using an experimental set up constructed for this work. Circular and square cross-sectional channels were tested using various deformable materials. Experimental results were compared with theoretical distributions, and several analogies were highlighted and discussed. Special tools were designed and manufactured to study experimentally the normal stresses at contact surfaces using the so called “Pressure Pin Technique”. Also, an experimental apparatus has been built to simulate the potential implementation of UREAD devices against the occurrence of heavy impacts and the effect of the energy absorber was experimentally measured at the instant of ground impact.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The optimisation of flexible impact-protection systems for varying strain rates and energies.

The need for smarter and active, energy absorbing systems designed especially for human protection applications has sparked interest in highly strain rate sensitive compounds. This thesis describes the iterative design, development and optimisation of a novel form of energy absorbing, body worn protection. The original contribution to knowledge is the development of a novel strain rate sensitive protection system incorporating synergetic internal architecture. Co-continuous blends of silicone based dilatant and thermoplastic elastomer have been developed through a recursive design process to develop a new material specifically optimised for body worn protection. Failure mechanisms were analysed, and from these results techniques have been developed to mitigate internal fracture mechanisms. This enabled the development of a strain rate sensitive material utilised with an internal architecture. The novel material properties were examined and developed using monolithic samples, tested at a variety of energies, speed and environmental conditions. Methods for designing and developing auxetic structures that work synergistically with the new material have been developed. The novel system has also been combined with textiles, and the merit of this combination explored. An improvement in performance has been validated, as well as a design improvement through being able to attach parts directly to garments. The resulting impact protectors are applicable over a range of strain rates. Systems have been designed to incorporate this novel technology in pre-production prototypes in three selected market areas, which typify low, medium and high impact speeds. The work also explores the systems ability to manage multiple impacts at the same location with a surprisingly low loss in performance, effectively making a protector that can withstand repeat impacts. This work has contributed to the methods previously used in testing personal protective equipment. The techniques developed in this work have enabled new revision of these PPE standards, as well as directly contributing to two new standards.Open Acces

The mitigation of primary blast injury

While effective against penetrating threats, ballistic armour may not mitigate primary blast injuries inflicted by the pressure wave. It remains poorly understood whether such armour improves blast clinical outcome for the wearer. The aim of this work was to deepen understanding of the nature of modern primary blast injuries, potential materials appropriate for personal blast protection and the influence of hard ballistic plates on expected survivability. The modern prevalence and severity of blast in the civilian environment was investigated by carrying out a meta-analysis of injured populations. The occurrence of primary blast injuries strongly depends on the ventilation of the attack environment. As the rate of pulmonary injury for Improvised Explosive Device attacks is approximately 9%, it is apparent that the blast attenuating capability of thoracic armour is of importance. The blast mitigation performance of polyurethane-based foams, hydrogels and a hard ballistic plate were assessed using a shock tube. The foams and hydrogels were manufactured and mechanically characterised across strain rates from 0.01–1600/s covering regimes relevant to both load-bearing and blast loading scenarios. While reticulated polyurethane foam enhanced the peak blast pressure, the hydrogels dissipated blast energy through brittle fracture. A ballistic gelatine human thorax surrogate was used to evaluate the clinical significance of the mitigation, and the blast loading of the gelatine computationally modelled. The hydrogels yielded a 90% reduction of peak pressure compared to the unarmoured case, comparable to values reported for water-based mitigation systems. By comparison, the addition of a ballistic plate with zero air gap increased lethality from values up to 50% in the unarmoured case to values up to 99%. Under the highest amplitude and duration blast loading, this corresponded to an increase of the delivered peak pressure and impulse to the surrogate of 52% and 27%, respectively, compared to the unarmoured case. Introduction of an air gap between the surrogate and armour further increased the lethality risk to near 99% over the full range of loading conditions due to blunt impact of the plate. However, mitigation could be achieved by combining the ballistic plate with a reticulated foam backing layer greater than a critical thickness.Open Acces

Modular Composite Body Armor

Tasked with the development of a composite material profile for use in the application of body armor design, the team worked with with Desmark/Amerisewn to create a stab and slash resistant composite material. This report investigates the design, development, and analysis of such composite material, and details the accomplishments made by the team throughout the entire design process. The objective was to meet and adhere to the National Institute of Justice (NIJ) 0115.00 Standards, specifically the specifications described for a Protection Level III apparatus. Thinking beyond this scope, the initiative is to provide a more lightweight, flexible, reliable, and modular solution to threats encountered by law enforcement officials in regards to slash and stab attacks, with a primary concern being those implemented by a knife or spike-like object. Corresponding manufacturing and experimentation procedures are included for analyzing the implicit dynamic penetration resistance and associated mechanical behaviors of the configured composite material. Through this analysis, a numerical method pertaining to the design and prediction of a multi-laminate composite material’s mechanical behavior, given an impact due to a weapon/implement mentioned above, aided in a final solution that adheres to both the items described within the NIJ 0115.00 Standard as well as design specifications corresponding to the product. Proposed to adhere to these requirements, the team developed a composite material that applies a multi-laminate design to create the desired product characteristics. The carbon fiber epoxy resin solution has an overall profile thickness of 0.495 inches and an estimate total weight of approximately 2.38 lb. A manufacturing method for producing such composite material is also explained in this report. Further analysis and testing of the was conducted through means of numerical analysis. A composite program developed by the team using MATLAB was used to calculate the mechanical characteristics of the composite using data inputs collected by experimental methods. The program will then assess the respective stress and strain relations through the entire composite profile. This gave insight to where the material will fail and under what load, and is a useful tool in determining the failure conditions, as well as identifying materials that do not contribute to the overall integrity of the composite. Several methods of experimentation, both physically and numerically, were conducted in order to validate the performance and adherence to design specifications. Ultimately, the carbon fiber/epoxy composite material adheres to National Institute of Justice’s 0115.00 Protection Level III Standard the most effectively and efficiently, minimizing the depth of puncture to less than 1/4 and 3/4 past the backing material due to a force applied at the strike face of 43.0J and 65.0J respectively

Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included

Development of a helmet liner for protection against blast induced trauma

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 211-215).Traumatic brain injuries caused by shock waves have attracted increased medical and scientific attention due to the large percentage of combat troops that have sustained such injuries in recent conflict theatres. To this day, the knowledge in the fields of causes, effects and identification of traumatic brain injury is limited. The use of advanced body armor has decreased the number of fatalities from fragments observed in previous military operations, resulting in the increase of non-fatal brain injuries from shock waves. The purpose of this project is the advancement of the knowledge in the field of shock wave mitigation strategies and the development of a helmet liner for protection against blast induced trauma. The proposed helmet liner design is based on the introduction of solid and fluid filler materials inside channels opened in the interior of a foam liner in order to enhance the attenuation of incoming shock waves. Primary investigated attenuation mechanisms include acoustic impedance mismatches between the filler and foam material interfaces, viscous effects of fluid fillers, porosity and particle size of solid filler materials. Specific goals of this research project include the reduction of the peak pressure and pressure gradient of the transmitted wave through the helmet liner and the enhancement of the spatial distribution of the energy of the incoming shock wave.(cont.)This research effort employed both shock tube experiments and numerical studies in order to investigate the effectiveness of the proposed helmet liner design. Quantitative results have shown that the use of high density filler materials result in higher attenuation levels than low density materials while comparing to solid foam control samples. The peak transmitted overpressure and pressure gradient were significantly reduced with the use of high density materials while the duration of the positive phase was increased. This response resulted in lower overall impulse values of the transmitted wave. The use of high density filler materials also results in superior frequency distribution.by George Alexander Christou.S.M

Applications of Finite Element Modeling for Mechanical and Mechatronic Systems

Modern engineering practice requires advanced numerical modeling because, among other things, it reduces the costs associated with prototyping or predicting the occurrence of potentially dangerous situations during operation in certain defined conditions. Thus far, different methods have been used to implement the real structure into the numerical version. The most popular uses have been variations of the finite element method (FEM). The aim of this Special Issue has been to familiarize the reader with the latest applications of the FEM for the modeling and analysis of diverse mechanical problems. Authors are encouraged to provide a concise description of the specific application or a potential application of the Special Issue