Search

The use of the porous Polylactic acid (PLA) for tissue engineering has gained the attention of the researchers worldwide. In this work, PLA tubes were extruded using CO 2 as a foaming agent. The foaming of the PLA tubes at various extruder screw rotational speed and different CO 2 pressure are studied in this work. Subsequently, morphological characterization and surface hydrophilicity studies of the tubes were carried out. It is be found that with an increase in the screw rpm, the contact angle first decreases and reaches the lowest value and then increase with the increase in screw rpm. Similarly, the effects of screw rpm and gas pressure on cross-sectional morphology and FTIR spectra were observed indicating an increase in crystallinity. [ABSTRACT FROM AUTHOR]

Magnesium and its alloys are getting more attention in the field of tissue engineering as it is biodegradable as well as biocompatible. An open cell structure in particular offers the advantage of body fluid transportation through it and allows the growth of new tissues. Open cell Mg foams with pore interconnectivity are difficult to fabricate from conventional techniques. In the present work, a novel approach has been successfully developed to fabricate the open cell Mg structures with pore interconnectivity using powder metallurgy route and Ti-woven wire mesh as a space holding material. Pore morphology and percentage porosity can be easily altered by adjusting the Ti-wire diameter and shape of construct. Ti-woven wire mesh in the shape of netted wire gave the best result in terms of homogeneity of pores and strength. Maximum porosity achieved is 60% and ultimate tensile strength is measured to be 78 MPa for the porous structure. [ABSTRACT FROM AUTHOR]

Abstract: A new mechanism for biaxial tension tests was developed for loading an in-plane reinforced composite laminate or any injection-molded polymeric specimen simultaneously in two principal directions. This mechanism can be adapted to any uniaxial tension test machine and, thereby, it can reduce the cost of conducting tests on expensive dedicated machines. The fixture provides a uniform state of equibiaxial tension, necessary for characterizing the biaxial state of loading on any polymeric material system and it can also be reconfigured to test non-equibiaxial tension over a short range. The mechanism is presently utilized for understanding the failure behavior of injection molded short fiber polyamide and nanoparticle-reinforced PP thermoplastic composites. [Copyright &y& Elsevier]

Abstract: A three-dimensional macro-mechanical finite element (FE) model is developed to study the machining response of unidirectional (UD) carbon fiber reinforced polymer composites. This study is conducted for a range of fiber orientations, depths of cut and rake angles both experimentally as well as numerically. In the FE model the material properties are assumed as degraded based on the three-dimensional Tsai-Hill failure criterion. Cutting/thrust forces obtained from the FE simulation matches well with the experimental observations. Cutting force increases with fiber orientation and depth of cut but is less influenced by rake angle. Chip formation mechanism is observed under an optical microscope and is compared with FE simulation results. The chip formation mechanism predicted by FE simulations has a good agreement with experimental observations. [Copyright &y& Elsevier]

Abstract: In this second part of a two-part paper, the failure mechanism of polypropylene (PP)/nanoclay composite under fracture loads is presented. The PP/nanoclay composite was prepared via melt compounding in a twin-screw extruder. Maleic anhydride grafted polypropylene (MA-g-PP) was used as a compatibilizer to improve the dispersability of the clay. The PP/clay nanocomposite was characterized by XRD and SEM. XRD results show possibilities of exfoliation, and SEM studies rule out large-scale particle agglomeration. Fractographic observations of PP/clay nanocomposite at lower loading rates reveal that excessive fibrillation and impregnated fibrils arrest crack propagation, and the fracture occurs by void initiation at larger clay particles. As the loading rate increases, crazes combined with voids to accelerate crack propagation. At higher loading rates, cleavage type brittle fracture is observed. [Copyright &y& Elsevier]

Abstract: Polypropylene (PP)/Montmorillonite (MMT) nanoclay based composite was prepared by melt compounding with maleic anhydride grafted polypropylene (MA-g-PP) as a compatibilizer in a twin-screw extruder, and the test specimens were injection molded. Mechanical properties such as tensile modulus, flexural modulus, yield strength and maximum percent strains were measured for pure PP and PP based nanocomposite to establish the effect of clay platelet reinforcement. The fracture properties were measured by using the essential work of fracture (EWF) method. PP/clay nanocomposite shows 25% improvement in specific EWF compared to pure PP. The variation of EWF parameters with loading rate is discussed, whilst the mechanisms of fracture are considered in a subsequent paper. [Copyright &y& Elsevier]

Abstract: The chip formation mechanism in orthogonal machining of unidirectional glass fiber reinforced polymer (UD-GFRP) composites is simulated using quasi-static analysis. Dynamic explicit finite element method with mass scaling is used for analysis to speed up the solution. A two-dimensional, two-phase micromechanical model with elastic fiber, elasto-plastic matrix and a cohesive zone is used to simulate the debonding interface between the fiber and the matrix. The elements of the fiber are failed once the maximum principal stress reaches the tensile strength and the matrix elastic modulus is degraded once the ultimate strength is reached. The effect of fiber orientation, tool parameters and operating conditions on fiber and matrix failure and chip size is also investigated. The degradation of the matrix adjacent to the fiber occurs first, followed by failure of the fiber at its rear side. The extent of sub-surface damage due to matrix cracking and interfacial debonding is also determined. [Copyright &y& Elsevier]

In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage. • The influence of hybization on the high strain rate resposne of thermoplastic composites. • Intra-ply hybridization excels over inter-ply hybridization. • Placement and direction of yarns is crucial in intra-ply hybridization. • Higher areal density fabrics are replacable with hybrid fabrics of lower areal density. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of the High Strength Low Alloy (HSLA) Steel before and after heat treatment was examined experimentally by performing quasi-static and high strain rate testing at room temperature and cryogenic temperatures. The high strain rate tensile testing of the material was performed on a Split Hopkinson Tensile Bar (SHTB) setup. A customized liquid nitrogen chamber equipped with UTM and SHTB was used to perform the cryogenic temperature testing. The stress–strain response of the material under different loading conditions was recorded and a modified Johnson–Cook material model was derived. It was observed that the flow stress of the material increased when tested at a high strain rate and it further increased at a cryogenic high strain rate loading environment. The microstructure of the material before and after heat treatment was also observed to identify the dominant phase change in microstructure contributing towards improvement in strength after heat treatment. The failure analysis of each category of the samples was examined under the Scanning Electron Microscope (SEM) after the testing. The formation of small and deep dimples for as-received samples and bigger and shallow dimples for heat-treated samples distinguished the type of failure between the quasi-static, high strain rate and cryogenic high strain rate material testing. • High Strength Low Alloy Steel (HSLA) were characterized at Quasi-Static and high strain rate tensile testing at room temperature and cryogenic temperature in both annealed and post heat treated conditions. • The customized Split Hopkinson Tensile Bar equipped with liquid nitrogen chamber and on-board temperature measurement system was developed to perform high strain rate cryogenic testing of HSLA steel. • The fractured surface of annealed and post heat treated samples were examined to understand the underlying effect contributing towards improvement in mechanical properties of the HSLA steel. • The modified Johnson–Cook material model parameters were derived based on the experimental results. The numerical simulations were performed to verify the developed constituent model. [ABSTRACT FROM AUTHOR]

Highlights • A novel single step biaxial expansion method is used for bioresorbable tube fabrication. • Biaxially expanded tubes have better radial compressive properties. • Brittle behaviour of PLA changes to ductile by addition of 5 wt% PCL. Abstract Bioresorbable stents is going to become the future modality for the treatment of coronary artery disease (CAD). However, the main limitation of the polymeric stent is its poor mechanical properties. For the proper functioning of a stent in the artery; it is required to enhance the radial stiffness of the polymeric stent. Polymeric tube manufacturing is the first and most important step in the stent manufacturing process. Usually, post processing operation which enhances the mechanical properties such as annealing, blowing and die drawing near glass transition are used after tube extrusion. In this study, along with conventional tube extrusion process (SE), a single step biaxial expansion method (BAE) was employed during the tube extrusion. The effect of manufacturing method on the radial compressive strength of the extruded tubes is thereby evaluated. For further determining the tubes radial resistive force, parallel plate crush testing as per ISO 25539-2 was performed and it is observed that tubes extruded by BAE method have better performance during crush testing as compared to the SE tubes of the same material. SEM was used for observing the cross-sectional morphology of the Cryo-fractured surface of fabricated bioresorbable tubes. [ABSTRACT FROM AUTHOR]

This study systematically investigates the effect of Shear Thickening Fluid (STF) treatment on the high strain rate properties of UHMWPE (Ultra High Molecular Weight Poly Ethylene) composites. Spherical nanosilica particles of size 100 nm were used for the synthesis of STF. The high strain rate impact studies were accomplished on in-house designed and fabricated Split Hopkinson Pressure Bar (SHPB) experimental set-up. Compression moulded UHMWPE variant Gold Shield ® was used as the ballistic composite. Both STF-treated as well as neat Gold Shield ® specimens were subjected to high strain rate impact testing. From the experimental results and Fractography studies it was revealed that STF treatment enhanced the ballistic resistance of Gold Shield ® composite material. In the SHPB experiments, the improved ballistic performance of STF-treated Gold Shield ® specimens was manifested in terms of higher peak stress, specimen strain rates and impact toughness. [ABSTRACT FROM AUTHOR]

Shear thickening fluids (STFs) are a special class of field responsive fluids which exhibit change of phase from liquid to solid when subjected to imposed shear. This remarkable characteristic of STFs has led to their application in soft body armor technologies, leading the development of concept of Liquid Body Armors (LBAs). LBAs extensively rely upon the symbiotic relationship between STF and high strength FRP (Fiber Reinforced Polymer) composites comprising of high tenacity fibers such as Kevlar, UHMWPE (Ultra High Molecular Weight Poly Ethylene) etc. Although in the past, STFs have been widely characterized by rheometers at low strain rates (≤10 3 s −1 ), but in actual practical scenarios, body armours encounter much higher strain rates (of the order of 10 5 –10 7 s −1 ) under a ballistic impact. The main objective of this study is to capture the dynamics of STFs at such high strain rates by employing Split Hopkinson Pressure Bar (SHPB) technique. The STF sample was synthesized by dispersing 67.5 wt.% of 100 nm silica powder in Poly Propylene Glycol (PPG) and ethanol, using ultrasonic homogenization method. The mechanical response of STF was studied at high strain rates in terms of the stress-strain behavior and variation of the impact toughness with the loading rate of the fluid specimen. It was observed that the impact toughness of STF increased progressively with the specimen loading rate. The peak stress and peak strain rate attained in the SHPB tests were 147 MPa and 22,100 s −1 , respectively. The characteristic transition time of STF was found to be in the range of 13–25 µs. [ABSTRACT FROM AUTHOR]

In the present work, dynamic compression response of polypropylene (PP) based composites reinforced with Kevlar/Basalt fabrics was investigated. Two homogeneous fabrics with Kevlar (K3D) and Basalt (B3D) yarns and one hybrid (H3D) fabric with a combination of Kevlar/Basalt yarns were produced. The architecture of the fabrics was three-dimensional angle-interlock (3D-A). Three different composite laminates were manufactured using vacuum-assisted compression molding technique. The high strain rate compression loading was applied using a Split-Hopkinson Pressure Bar (SHPB) set-up at a strain rate regime of 3633–5235/s. The results indicated that the dynamic compression properties of thermoplastic 3D-A composites are strain rate sensitive. In all the composites, the peak stress, toughness and modulus were increased with strain rate. However, the strain at peak stress of Basalt reinforced composites (B3D, H3D) decreased approximately by 25%, while for K3D specimens it increased approximately by 15%. The K3D composites had a higher strain rate as compared to the B3D and H3D composites. In the case of K3D composite, except strain at peak stress, remaining dynamic properties were lower than the B3D composite, however, hybridization increased these properties. The failure mechanisms of 3D-A composites were characterized through macroscopic and scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

This paper investigates the characterization of in-plane shear properties of thermoplastic composites reinforced with Kevlar/basalt fabrics. Different fabrics had architectures of two dimensional plain woven (2D-P) and three dimensional angle-interlock (3D-A). Intralayer hybridization was performed during the weaving of the fabrics with the combination of Kevlar and basalt yarns. Five 2D-P and three 3D-A composite laminates were manufactured with polypropylene (PP) as a matrix, using compression molding. Iosipescu shear tests were carried out to evaluate the in-plane shear properties. The experimental results revealed that the shear properties including shear modulus, shear strength and shear failure strain of homogeneous composites were improved by 6.5–14.9%, 4.3–19.7%, and 3.2–46.7%, respectively. Similarly, change in the fabric architecture from 2D-P to 3D-A also enhanced the shear strength and shear failure strain by 32.0–41.6% and 7.2–22.5%, respectively. Intralayer hybrid composites had better in-plane shear properties than the interlayer hybrid composites. The fracture morphologies of the specimens were examined by scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

The present study compared the tensile and low velocity impact (LVI) response of Kevlar/basalt fabrics. Homogeneous and hybrid fabrics with structures of two dimensional plain woven (2D-P) and three dimensional angle-interlock (3D-A) were woven with Kevlar and basalt yarns. Interlacing of brittle basalt yarns with high-ductility/high-toughness Kevlar yarns enhanced the tensile strength of 2D-P fabrics by 5.39–50.29% and 3D-A fabrics by 14.80%. Similarly hybridization enhanced the energy absorption of 2D-P fabrics by 8.58–37.71% and 3D-A fabrics by 13.45–20.14%. Change in the architecture from 2D-P to 3D-A also enhanced the tensile and impact resistance of fabrics. Different failure modes induced due to tensile and LVI loads were identified. [ABSTRACT FROM AUTHOR]

Kevlar ® fabric reinforced plastics (KFRPs) are specialized composites with multiple layers of fabrics (∼ranging from 20 to 50 layers) designed for high impact applications. In this work, Kevlar-129 fiber was reinforced with polyetherimide (PEI) and polypropylene (PP) to obtain two groups of laminates in three configurations i.e. 16, 24 and 30 layers. Holes of diameter 11.6 mm were profile cut using fiber laser machining system operating at 1070 nm wavelength. Effects of polymeric matrix on the failure of the Kevlar – polyetherimide (K-PEI) and Kevlar – polypropylene (K-PP) laminates were characterized by studying the following: (i) threshold laser power required to make the holes (ii) surface morphology using scanning electron microscopy (iii) damage zone along the laser cut path using scanning acoustic microscopy and optical microscopy. K-PEI laminates underwent material separation at much lesser line energy (ratio of laser power to velocity) than K-PP laminates during laser machining. Scanning electron microscopy (SEM) was used to further analyze the laser cut surfaces. A prominent observation on the laser-irradiated surface was: less recast/resolidified polymer covered the Kevlar fabric in K-PEI as compared to a thicker polymeric layer in K-PP. Heat affected zone and damage factors were evaluated using scanning acoustic microscopy (SAM). Surface roughness and kerf width were also analyzed to understand the effect of laser machining of Kevlar laminates. [ABSTRACT FROM AUTHOR]

The present work reported the mechanical characterization of novel polypropylene (PP) composites reinforced with three-dimensional angle-interlock (3D-A) Kevlar/basalt fabrics. Two homogeneous fabrics with Kevlar (K3D) and basalt yarns (B3D), and a hybrid fabric (H3D) with a combination of both Kevlar and basalt yarns were produced. Three types of two layer 3D-A composites were manufactured using vacuum-assisted compression molding method. Static tensile and in-plane compression tests were carried out on the manufactured composites. The mechanical behavior of the three 3D-A composites was compared in terms of stress-strain response, elastic modulus, strength and failure strain. Influence of hybridization on the mechanical behavior of the 3D-A composites was also studied. Significant improvement in the tensile behavior of 3D-A homogeneous composites was observed due to hybridization. Meanwhile, there was no considerable improvement in in-plane compression behavior. The damage patterns for in-plane compression loading were examined through scanning electron microscopy (SEM) to explore the possible damage patterns such as matrix cracking, fiber failure, delamination and deformation. Numerical simulations were carried out using ABAQUS/Standard, by implementing a user-defined material subroutine (VUMAT) based on the Chang-Chang linear orthotropic damage model. Good agreement between experimental and numerical simulations was achieved in terms of damage patterns. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations are carried out to determine the low velocity impact (LVI) response of three different polypropylene (PP) composites. Three dimensional (3D) angle-interlock fabrics with Kevlar, basalt and a hybrid combination of both are produced. 3D composites are manufactured with these three fabrics using vacuum-assisted compression molding process with PP resin. LVI tests are conducted using a drop-weight impact equipment at the energy level of 240 J. The LVI response of the three 3D-PP composites is compared in terms of peak force, energy absorption and damage modes. The experimental results indicate that the basalt 3D composites showed 6.62–13.73% higher peak force and H3D composites absorbed 7.67-48.49% more energy than the remaining composites. Results indicate that there is a considerable enhancement in the energy absorbing capability of hybrid composites as compared to Kevlar/PP and basalt/PP composites. Numerical simulations are carried out using the commercial finite element (FE) code ABAQUS/Explicit. A user-defined material subroutine (VUMAT) based on Chang-Chang linear orthotropic damage model, is implemented into the FE code. Good agreement between experimental and numerical simulations is achieved in terms of impact response characteristics. [ABSTRACT FROM AUTHOR]

In this study, low velocity impact (LVI) behaviors of composite laminates reinforced with fabrics of different architecture are investigated. Three kinds of fabric architecture, namely, two-dimensional plain woven (2D-P), three-dimensional orthogonal (3D-O) and three-dimensional angle interlock (3D-A), are prepared with Kevlar 29 (Kevlar) yarns. Composite laminates are manufactured with Kevlar fabrics and polypropylene (PP) resin. These composites are impact tested at 4 m/s and 6 m/s impact velocities. The post-impact response of the composites of different fabric architecture is studied. The results revealed that the impact resistance is mainly dependent on the in-plane stiffness of the laminates. The energy absorption ability is predominantly influenced by the existence of yarns in the thickness direction. The 3D composites absorbed 14–26% higher energy than the 2D laminates. Especially, 3D-A laminates exhibited a higher peak load (14.21–30.25%), more energy absorption (12.7–26.2%) and lower cone formation at the back of the target (25–39%) as compared to 3D-O and 2D-P composites. [ABSTRACT FROM AUTHOR]

In this study, experimental investigations on Kevlar fiber reinforced polypropylene (PP) woven composites under high strain rate compression loading are discussed. Kevlar/PP composite laminates with 8 and 24 layers are fabricated using vacuum assisted compression molding technique. Maleic anhydride grafted-PP (MAg-PP) is added to PP to improve the interfacial property between Kevlar fiber and PP resin. The through-thickness properties at high strain rates from 1370 to 6066 s −1 are obtained using split Hopkinson pressure bar (SHPB) setup. The behavior of PP resin is found to be different than the commonly used thermoset resins, such as epoxy. Dynamic stress–strain relations are drawn to reveal the mechanical properties at high strain rates and these relations appear to be rate sensitive. As a result, the peak stress increased by three times, toughness increased by almost ten times and strain at peak stress increased by as much as two times with an increase in the strain rate. The final failure of the specimens is examined by scanning electron microscopy (SEM) to explore the possible failure mechanisms such as, delamination, fiber failure and shear fracture. [ABSTRACT FROM AUTHOR]

The ballistic impact response of thermoplastic-based composite armors made from Kevlar ® fabric and polypropylene (PP) matrix has been investigated against ballistic test standard NIJ-STD 0106.01 Type IIIA. Kevlar ® fabrics of different architectures, namely 2D plain woven, 3D orthogonal and 3D angle interlock fabrics, were produced and used as reinforcements to fabricate composite armor panels, using compression molding technology. Interfacial property between PP and Kevlar ® was improved by adding a coupling agent called maleic anhydride grafted PP. Reduced density was observed in Kevlar ® thermoplastic-based composites as compared to that of the thermoset-based laminates. Ballistic impact tests were imparted with 9 mm full metal jacket (FMJ) on armor panels having different fabric architecture. Ballistic test results revealed that 2D armor was 2.4–7% more susceptible to damage than 3D armors. Hydrocode simulations were carried out using ANSYS AUTODYN v. 14.0 to obtain an estimate for the ballistic limit velocity and simulate failure modes. Post-impact damage patterns obtained from the simulations were compared with the experimental results to assess the performance of the simulations. Good correlation between the hydrocode simulations and experiments was found, both in terms of failure modes and damage patterns. 3D composite armors were able to confront the 9 mm FMJ projectile; however, the 2D plain woven armors failed. The increase in the ballistic limit from 2D plain woven armor to 3D orthogonal and 3D angle interlock armors was 16.44% and 20%, respectively, indicating the effect of fabric architecture. [ABSTRACT FROM AUTHOR]

• High hardness steel (HHS) sheet with UHMWPE composite backing were tested against a hardened steel core projectile. • The projectile core was eroded by the HHS sheet and stopped in UHMWPE composite. • It is observed that only a core eroded to a certain length and weight by armor system can be defeated. • In numerical modeling core failure strain was determined from the residual weight of cores. • The numerical model can be used to evolve armor design. Thin high hardness steel sheets can be an alternative to expensive ceramic armor systems designed to defeat hardened core projectiles. A thin high hardness steel sheet backed with UHMWPE fiber-reinforced composite was ballistically tested against a 7.62 × 39 mm hardened steel core projectile in a single-stage gas gun. Thin steel sheets of 530 BHN hardness were adhesively bonded with UHMWPE fiber-reinforced composite to fabricate armor plates. Armor plates were able to defeat the projectile showing considerable potential. Tensile strength of steel sheet and UHMWPE-fiber reinforced ply was also determined. A detailed numerical simulation of the impact event was also performed to understand the phenomenon of defeat and penetration in greater detail. The numerical model was calibrated from the recovered projectile's core after the ballistic test. [ABSTRACT FROM AUTHOR]

• Vacuum compression moulded Basalt-Polyeteherimide (PEI) composites manufacturing. • Optimization of Basalt-PEI composite manufacturing moulding parameters. • Basalt-PEI composite under quasi-static and dynamic high strain rate loading. • Elastic recovery of Basalt-PEI composite can help in reflecting the blast wave. High temperature blast and ballistic resistant light weight fibre reinforced plastic composites are very much in demand. Accordingly, the present investigation is focused on the quasi-static and high strain rate behaviour of Basalt/Polyetherimide (PEI) composite. Nine different types of composite samples were fabricated by compression moulding. The moulding pressures and temperatures were varied in the range of 15–25 bars and 325 °C−375 °C, respectively. Quasi-static testing was done at the rate of 3 mm/min to establish the optimum moulding parameters. High strain rate compression tests in the strain rate range of 900/s−3200/s were performed on the optimum moulded composite specimens. High strain rate testing revealed that 40 layered Basalt/PEI composite moulded at 25 bar pressure and 350 °C attained highest stress of 932 MPa whereas, the same was found to attain 446 MPa under quasi-static loading conditons. Thus, establishing the rate depedency of Basalt/PEI composite. Damage studies revealed that Basalt/PEI undergoes brittle damage, typically resulting in shear plane angle of 42°−45°. SEM micrographs revealed brittle fibre failure and matrix free fibre bundles, indicating the importance of process parameter optimiation. [ABSTRACT FROM AUTHOR]

The present study deals with the quasi-static and high strain rate characterization of Kevlar-129 based thermoplastic composites. Two different thermoplastic matrices, namely, Polypropylene (PP) and Polyetherimide (PEI) were used to manufacture composite laminates. Quasi-static compression tests were performed at strain rates of 0.041 s−1 and 0.045 s−1. High strain rate tests were performed using a split Hopkinson pressure bar apparatus within the strain rates ranging from 2548 s−1 to 4379 s−1. Stress-strain relations reveals the rate-sensitive behaviour of composites. Kevlar/PP (K-PP) showed higher peak stress under quasi-static loading as compared to the high strain rate test. Comparable peak stresses were revealed under quasi-static and high strain rate loading for Kevlar/PEI (K-PEI) composite. Also, high strain rate compression properties such as peak stress, peak strain and toughness of K-PP were 25%, 27% and 6% higher than that of the K-PEI composite. The failure mechanisms of both the composites were characterized through macroscopic and scanning electron microscopy. K-PP failed majorly due to matrix crush and fibre failure while K-PEI failed due to shear cracking. Damage study reveals that a single fibre based composite system can be tailored to act as an energy-absorbing or dissipating material system by varying the thermoplastic matrix materials. • Static and dynamic compressive properties of Kevlar reinforced high-performance polymers. • Kevlar/Polypropylene outperforms over Kevlar/Polyetherimide under both the quasi-static and high strain rate loads. • The quasi-static strength of Kevlar/Polypropylene is 25% higher than its high strain rate strength. • Polypropylene matrix results in ductile failure, while the Polyetherimide matrix results in brittle failure. [ABSTRACT FROM AUTHOR]

Modification of Polylactic acid (PLA), a biopolymer, is a strategy still to be fully explored for the next generation of bioresorbable vascular stent (BVS) biomaterials. With this focus, inclusions upto 5% of Polycaprolactone (PCL) and Magnesium in PLA were tested in the rat subcutaneous model and their cellular and tissue interactions characterized, specifically with respect to inflammatory response, angiogenesis and capsularization. The cytokines IL6, TNF Alpha and IL-1Beta were estimated in the peri-implant tissue, all of which showed a non-significant difference between the non-implanted animals and those containing PLA by 8 weeks, speaking to the benign nature of PLA as an implant biomaterial. Both modified materials, had increased macrophage counts and cytokine levels, except IL6 at 8 weeks. Vascularization only at 8 weeks in PLA PCL containing tissue was significantly higher than pure PLA, which may be more carefully controlled along with the material hydrophobicity for possible efforts towards therapeutic angiogenesis. Capsule thickness, measured by staining with both Hematoxylin & Eosin and Masson's Trichome did not show any differences between materials, including PLA. [ABSTRACT FROM AUTHOR]

Abstract: In this research article, novel porous microcellular ABS foams were fabricated and subsequently investigated for their morphological attributes. Initial research focuses on developing ultra-low density closed cell foams through cyclic microcellular foaming process. First stage foaming process develops microcells which affect the second stage of the batch foaming process. Hence, the effect of repeated foaming process on foam density and its morphology are discussed. Subsequently, ultrasound excitations were utilized to rupture the closed cell walls, thereby developing porous structure. The combined cyclic solid-state foaming and ultrasound excitation provides a way to fabricate ultra-low density porous polymers. [Copyright &y& Elsevier]

Quasi-static tensile test of UHMWPE fiber-reinforced composite laminate is challenging to perform due to low interlaminar shear strength and low coefficient of friction. Tensile tests proposed in the literature were conducted and limitations associated with each method led to the evolution of a new method. Tensile test of single-ply was realized as the best representative of tensile strength of a composite than tensile test of UHMWPE laminate. A fixture was developed for single-ply tests which increased friction and provided the mechanical constraint to slipping. The fixture is easy to fabricate and has provided repeatable results for eight grades of UHMWPE fiber-based (0/90) fabrics. Reported tensile strengths are in quite high range of 900–1500 MPa. • Ballistic composites are quite different from structural composites. • Tensile strength difficult to determine with standard methods. • All available methods tested for efficacy. • A new method is suggested for efficient testing. • Properties of wight commercial grades determined by suggested method. [ABSTRACT FROM AUTHOR]