Design bio-inspired composite structure subjected to blast loading

This paper investigates the behaviour of a bio-inspired finite element composite model (that mimics the structure of nacre, the inner layer of molluscan shells) under blast loading. Nacre, which has attracted the attention of researchers over the past few decades, comprises 95% aragonite, brittle voronoi-like polygonal tablets that are joined by an organic matrix and arranged in a brick and mortar type structure. The best attempt made thus far in mimicking such complex geometry involved rebuilding the tablet contours via optical imaging. This method, which practically copies the nacreous structure, offers no control over the geometry, making it difficult, if not impossible to eventually develop composites that mimic nacre. To this end, the finite element model developed herein was constructed using voronoi diagrams and geometric algorithms capable of automatically generating staggered layers of voronoi-like aluminium tablets bonded together by a vinylester adhesive layer. Many studies have led to the belief that the magnificent toughness of nacre is mainly attributed to the inter-platelet adhesive bonds. Results obtained from the finite element analysis show that this is indeed true, and it is imperative that the adhesive bond exhibits adequate toughness in order to be able to spread damage across the entire composite, thereby delaying localised failure

PEMBUATAN MODEL APLIKASI REMINDER MUTABA'AH AMAL YAUMIYAH STUDI KASUS YAYASAN TENDA VISI INDONESIA

Tenda visi sebagai sebuah lembaga yang bergerak di bidang sosial-pendidikan tentunya memiliki banyak program kerja. Salah satu program kerja dari Tenda Visi adalah Mutabaah Amal Yaumiyah. Mutabaah Amal Yaumiyah merupakan kegiatan rutin setiap anggota Tenda Visi dalam hal ibadah. Terdapat kesulitan dalam pelaksanaan program Mutabaah Amal Yaumiyah yaitu sulitnya mereka data kegiatan amal yaumiyah yang sudah dilakukan oleh anggota karena anggota terkadang lupa memberikan catatan amal yaumiyah-nya. Selain itu anggota Tenda Visi juga terkadang lupa untuk melakukan amal yaumiyah yang harus dikerjakan. Reminder/pengingat bisa dikatakan sebagai aplikasi yang berfungsi untuk memberi tahu pada hari/waktu itu ada sebuah kegiatan atau hal yang harus dilakukan. Sebelum reminder memberikan informasi mengenai kegiatan yang harus dilakukan, pengguna melakukan pengaturan jadwal dan kegiatan terlebih dahulu. Reminder mutabaah amal yaumiyah merupakan solusi yang dapat membantu Tenda Visi dalam merekap kegiatan amal yaumiyah anggota, evaluasi terhadap kegiaatan amal yaumiyah yang sudah dilakukan anggota, serta dapat memberikan kemudahan kepada anggota dalam melaksanakan dan mendokumentasikan amal yaumiyah yang sudah dilakukan. Kata kunci : amal yaumiyah, reminder, aplikasi, tenda visi, kegiata

A bio-inspired composite system for protecting critical structural components from extreme loads

© 2017 Dr. Abdallah GhazlanAccidental and deliberate loads on civil and military structures continue to cause severe damage worldwide, along with catastrophic losses of human life. The significance of this problem is evidenced by high government spending on counter-terrorism, which has steadily increased over the past decade to several billion dollars. There is little evidence on the efficiency of such expenditures, which highlights the need for scientific intervention. This study seeks a solution from nature, which has optimised its structure over millions of years of evolution to survive extreme loads that arise from the harsh conditions of its environment. The attractive feature of natural structures is that they tend to minimise their weight by employing highly brittle minerals during their assembly but the overall structure boasts a fracture toughness that is several orders of magnitude greater. This makes natural structures highly attractive to the protective structural engineering discipline. The overarching aim of this research project is to develop a lightweight bio-inspired composite system (BCS) for protecting critical structural elements from extreme loads by identifying and mimicking the key strengthening and toughening mechanisms facilitated by the structural features of nacreous seashells. This aim spans three disciplines, namely extreme loading, biomimicry and computational geometry. Firstly, a comprehensive literature review is conducted on these three key areas to understand: 1) the physics of blast loading and shockwave dynamics; 2) the key toughening mechanisms that are employed in the armour system of nacreous seashells to protect their soft tissues from extreme loads; and 3) computational geometry techniques that can be employed to mimic several key features of these natural structures and translate them to protective structural systems. Building on this knowledge, a computational framework is developed to generate nacre-mimetic composite structures in a format that is recognised by computer aided design (CAD) and finite element programs. This framework can automatically construct and manipulate the geometry of the nacre-mimetic composite structure, which saves significant time by automating the modelling and manufacturing process. The framework utilises geometry manipulation and meshing functionalities that are already implemented in popular software packages, and implements additional subroutines where specialised functions are not available. For example, a specialised subroutine is required to automatically insert cohesive elements between polygonal bricks to model the nacre-like mortar. The geometry was developed to be transferrable to a CAD format such that the nacre-mimetic structure can be manufactured using rapid prototyping technologies such as 3D printing or laser cutting. Several analytical models were subsequently developed at the unit cell level to gain preliminary insight into the parameters responsible for the superior load transfer efficiency found in nacre. By extending current analytical studies conducted by researchers in the area of biomimicry, which mainly investigated the behaviour of nacre’s brick and mortar structure under planar tension, a shear lag approach was employed, which assumes that the tensile force applied to the bricks is transferred via shear through the mortar. As such, parametric studies were conducted to investigate the significance of the interfacial geometry and the overlap length between the bricks in adjacent layers, with the objective of quantifying the effects of these features on the energy absorbing capacity and load transfer efficiency in the composite structure. This preliminary study showed that the waviness of the interface improves the shear transfer efficiency in the mortar and maximises the load sharing efficiency between the bricks and the mortar. To this end, a more comprehensive numerical model was developed to mimic nacre’s polygonal brick and mortar structure more closely and account for fracture in the mortar, which has been observed experimentally. Voronoi diagrams, which are well-known in computational geometry, were employed to automatically generate different nacre-mimetic polygonal structures. This facilitated several key parametric studies for understanding the behaviour of the nacre-mimetic composite under quasi-static loading, whereby the numerical model was validated using experimental data available in the literature. These studies showed that the constitutive behaviour of the ductile mortar was responsible for the high toughness of nacre, which accounted for the hardening phase observed in the experimental stress-strain curve. This result was contrasted to the abovementioned simplified unit cell model, which indicated that the waviness of the interface and the overlap length between adjacent bricks played a key role. The shape of the bricks was also found to be significantly influential on the crack deflection and arrest capabilities in the mortar. The voronoi approach was again employed to investigate the dynamic behaviour and failure modes of a bio-mimetic polygonal brick and mortar panel under blast loading using finite element modelling techniques. Several parametric studies were conducted to establish the influence of different geometric and material parameters on the damage and load distribution in the composite. This model utilised the automated geometric construction and manipulation capabilities of the computational framework mentioned earlier. It was found that an increased number of layers in the brick and mortar structure increased the energy dissipated throughout the composite, which was much more prominent than a monolithic panel of equal mass. A bio-inspired polygonal brick and mortar composite structure was then manufactured from medium density fibreboard (MDF), which was bonded by a ductile polyurethane adhesive. The single edge notched specimen (SENT) utilised several key features found in nacre, namely the polygonal brick and mortar structure, reinforcing bridges between the bricks and the soft ductile adhesive bonding. The MDF panel was manufactured by utilising the automated computational framework mentioned previously and its behaviour was investigated under quasi-static loading. Compared to a brittle monolithic MDF specimen of equal mass, the nacre-mimetic composite showed significant improvements in ductility and energy absorbed. This was achieved by deflecting cracks away from the brittle bricks and into the ductile polyurethane mortar, which did not fracture at the conclusion of the test. The high potential of this study in terms of protective structures is evident because brittle non-structural materials that are abundantly found in structures, such as ceramic tiles, can be toughened to protect critical structural elements from extreme loads

Blast performance of a bio-mimetic panel based on the structure of nacre - A numerical study

2019 Elsevier Ltd Nacre, the tough protective layer of a mollusk seashell, has a fracture toughness that is several orders of magnitude higher than brittle aragonite, a ceramic that accounts for 95% of its composition. As such, it possesses characteristics that may be highly beneficial for protective structural applications. In this research, several structural characteristics from nacre\u27s brick and mortar-like microstructure are mimicked with the goal of enhancing the stiffness and fracture toughness of a monolithic ceramic panel under blast loading. These features include the mineral bridges connecting the adjacent brick-like tablets for enhancing the stiffness of the panel, the multi-layered structure for enhancing its toughness via crack bridging mechanisms and the growth bands between the nacreous tablet layers for deflecting cracks. The results from the numerical simulations showed that the nacre-like panel possesses superior energy dissipation over the monolithic ceramic panel, which thereby reduces the reaction forces transmitted to the supports and mitigates catastrophic failure. This has positive implications in terms of the capability of fine-tuning the structural characteristics of an armor system for defeating impulsive loads, by employing the principles adopted in the microstructure of a natural armor system

Advanced manufacturing methods for ceramic and bioinspired ceramic composites: A review

Ceramics and ceramic composites are often utilised for armour applications, where light weight and ballistic protection are essential. Recently, bio-inspired materials and composites for future armour applications are attracting increasing attention from researchers and engineers. In order to choose the suitable methods and techniques to fabricate ceramic and bioinspired ceramic composite armours cost-effectively, it is necessary to understand current techniques for manufacturing ceramic and ceramic composite products. In this paper, we provide a state-of-the-art review of advanced/potential manufacturing techniques available to fabricate ceramic and bioinspired ceramic composites. These methods encompass powder-based techniques (e.g., Selective Laser Melting/Sintering, Binder Jetting) used for prototyping porous ceramic structures, as well as vat polymerisation (e.g., Stereolithography, Digital Light Processing) and Slurry-Based Deposition (e.g., Direct Ink Writing, Fused Deposition Modelling), which are employed for fabricating dense ceramic parts

Dynamic increase factors for Radiata pine CLT panels subjected to simulated out-of-plane blast loading

© 2020 Elsevier Ltd The construction industry, which accounts for almost 20% of Australia\u27s carbon emissions, is responding to climate change by increasing the demand for sustainable and environmentally friendly materials. Cross-laminated timber (CLT) is an innovative eco-friendly engineering material that can satisfy this demand due to its excellent properties, including fire and seismic resilience, natural insulation and lightweight, to name a few. This study presents the results of 8 blast tests, which were conducted on two types of Radiata pine CLT panels sourced in Australia. The CLT panels were subjected to simulated blast loads from a shock tube apparatus. The dynamic increase factor (DIFE) of the panels was quantified by comparing their stiffness in the dynamic and static loading regimes. Single degree of freedom (SDOF) and numerical models were developed to predict the elastic response of the CLT panels. Interestingly, the SDOF model predicted DIFE from 1.12 to 1.57 whilst the numerical model predicted DIFE from 1.05 to 1.43. The experimental and analytical results can supplement the development of design guidelines for predicting the behavior of Australian Radiata pine CLT panels under blast loading

Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites

This paper investigated the effect of ceram powder on the properties of composite laminates based on glass fibres and phenolic resin. The amount of ceram in the polymer matrix was varied between 30% and 50% of the weight of resin. The density, void ratio, tensile strength, interlaminar shear strength, bond strength, bending modulus and glass transition temperature were studied, and the effect of ceram on these properties was assessed. A systemic decision-making strategy is applied to evaluate the optimal amount of ceram in the polymer matrix. Results showed that while the increase of ceram decreased the strength properties of the composite laminates, the bulk density and bending modulus increased. Moreover, the glass transition temperature increased by 32 °C with the addition of 50% (by weight of resin) ceram powder. The strategic decision-making approach suggested that a good balance of physical, mechanical, and thermos-mechanical properties can be achieved when ceram is added at a fraction of 50% of the weight of resin, and this amount is considered as optimal for designing laminated fibre composites

A bio-mimetic cellular structure for mitigating the effects of impulsive loadings – A numerical study

© The Author(s) 2020. Re-entrant and honeycomb cellular structures have shown potential for mitigating the effects of extreme loadings such as those imposed by impacts and near-range air blast. However, these cellular geometries can buckle locally and collapse in the immediate vicinity of the loading, which can limit their effectiveness as a protective element. These deficiencies can be addressed by mimicking alternate, naturally occurring, cellular structures, including that of the porcupine quill, which is studied here. The quill possesses several distinct features that effectively counteract buckling and bending, and minimise weight. This study mimics several structural features of the quill to develop a novel cellular design for counteracting air blast loads such as those associated with detonations of high explosives. The performance of the bio-mimetic structure is benchmarked against traditional hexagonal and re-entrant designs, which have been documented in the archival literature. The quill-inspired structure offers more design freedom than the traditional cellular geometries. By iteratively mimicking several of the structural features of the porcupine quill, an optimal balance between local buckling and collapse can be realised, which minimises the reaction on the target below and maximises energy dissipation