Superior Specific Strength Research Articles

On the peridynamic formulation for an orthotropic Mindlin plate under bending

Composite materials are becoming increasingly widespread across applications such as aerospace, automotive, wind and solar energy systems, on account of their superior specific strength and stiffness. There are still unresolved challenges in the structural analysis of composite materials in practical engineering applications, owing to their complex structures. Peridynamic theory is a robust technique for the analysis of composite structures; however, it is computationally costly. Structural idealizations are commonly applied in engineering applications to represent structures with a reasonable simplicity, thus reducing the computational cost. Idealization of a planar structure, such as a plate, reduces the number of peridynamic interactions to be solved. In this study, a peridynamic plate formulation of an orthotropic plate with transverse shear deformation is proposed. Peridynamic bond parameters are derived by localizing the peridynamic equations of motion and comparing them with equations of motion obtained using classical continuum mechanics. A failure theory is implemented in the formulation in order to perform crack propagation simulations. A MATLAB script is written using the proposed formulation for the solution of orthotropic plates under bending. The peridynamic solutions are obtained for both elastic deformations and failure prediction of pre-cracked plates, and are validated using finite-element analysis solutions.

Enhancement of sawing strategy of multiple surface quality characteristics in low power fiber laser micro cutting process on titanium alloy sheet

Being a promising non-traditional micro machining process laser micromachining may efficiently and fruitfully be used for hard machining materials without the hindrances of their hardness, toughness and brittleness. Superior specific strength, corrosion resistance and creep properties have made titanium alloy fit for many engineering applications as well as in medical purposes. High quality of cutting metal sheets to achieve intricate shapes and geometries etc has made laser to be an attractive tool and a popular mode. High cutting speed, high accuracy, narrow kerf and least material waste are the reasons for its high quality. Study and experimental analysis of the effect of sawing angle and constant Z height movement with other process parameters like power setting, duty cycle, scanning speed and pulse frequency related to the kerf taper and surface roughness of the 1 mm titanium alloy sheet (Ti-6Al-4V) have been done. Investigations on laser cutting for the attainment of optimization have found out better process control and better quality of final product.

Systematic design of high-strength multicomponent metamaterials

The emergence of additive manufacturing, along with the introduction of the concept of metamaterials, allows the synthesis of high-performance materials with superior specific strength. With recent advances in printing multi-material structures, the design space of metamaterials has exponentially grown. Variation in dimensions of the printed metamaterials due to limitations of the manufacturing process can drastically offset their performance compared to their original design. So far, the impact of deviations in the manufactured metamaterials and their effect on their final performance has not been studied systematically. There are also no guidelines for selecting materials in a multi-material lattice structure to achieve higher mechanical performance. Here, the strength and toughness of printed single- and bimaterial lattice structures with a combinatorial selection of materials and their sensitivity to the printing parameters are studied. We show that the exterior elements dominate the overall mechanical performance of the metamaterial compared to the internal elements. We found two regimes of slow and fast softening in periodic lattices. We study the sensitivity of the mechanical performance of the printed metamaterial to variations in the thickness of internal and exterior elements in detail.

Fiber Metal Laminate Structure, a good replacement for monolithic and composite materials

Lightweight materials such as aluminium alloys, magnesium alloys, and composite material present a significant possibility for applications in automobile and aerospace structures. In order to consider the feasibility of selecting and replacing such materials in the form of hybrid laminated materials, calculations and simulations are investigated with different lightweight materials such as single layer aluminium, fiber-reinforced composite materials, and the aluminium composite laminates, the carbon and glass cloth as the middle layer, under the constant force condition. The stiffness and deflections of these materials are discussed and compared in details. According to calculations, FE and experimental results validate that the deflections and the stiffness of different materials can be predicted well. In order to finalize the material selection, especially for aerospace-based components, the weight ratios are very determinative. Actually, a material with the superior specific stiffness and strength will be the best one considering some other limitations such as corrosion. Calculating the mass ratio of the suggested lightweight materials were done to find an appropriate one. In fact, these kinds of materials have the advantages of both metallic alloys and composites. In addition, in cases where corrosion resistance, environmental protection, fatigue resistance, and impact resistance are needed, FMLs can be the best choice.

Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance.

This review used a narrative summary of findings from studies that focused on isometric strength training (IST), covering the training considerations that affect strength adaptations and its effects on sports related dynamic performances. IST has been shown to induce less fatigue and resulted in superior joint angle specific strength than dynamic strength training, and benefited sports related dynamic performances such as running, jumping and cycling. IST may be included into athletes' training regime to avoid getting overly fatigue while still acquiring positive neuromuscular adaptations; to improve the strength at a biomechanically disadvantaged joint position of a specific movement; to improve sports specific movements that require mainly isometric contraction; and when athletes have limited mobility due to injuries. To increase muscle hypertrophy, IST should be performed at 70-75% of maximum voluntary contraction (MVC) with sustained contraction of 3-30 s per repetition, and total contraction duration of>80-150 s per session for>36 sessions. To increase maximum strength, IST should be performed at 80-100% MVC with sustained contraction of 1-5 s, and total contraction time of 30-90 s per session, while adopting multiple joint angles or targeted joint angle. Performing IST in a ballistic manner can maximize the improvement of rate of force development.

A review of Long fibre thermoplastic (LFT) composites

ABSTRACTLong fibre-reinforced thermoplastic or long fibre thermoplastic (LFT) composites possess superior specific modulus and strength, excellent impact resistance, and other advantages such as ease of processability, recyclability, and excellent corrosion resistance. These advantages make LFT composites one of the most advanced lightweight engineering materials and enable their increasing use in various applications. This review paper summarises the research and development work that has been conducted on LFT composites since their initial development. Different aspects of LFTs, such as process development, fibre orientation distribution (FOD), fibre length distribution (FLD), and their effects on the mechanical properties of LFT composites are described. The characterisation of the FOD and FLD in the LFT composites using advanced imaging technology such as high-resolution 3D micro-CT scanning technique is summarised. Research and development of LFT hybridisation and LFT additives are also discussed. Finally, conclusions are made and the future outlook of LFT composites is given.

Centimeter-sized Ti-rich bulk metallic glasses with superior specific strength and corrosion resistance

Since increasing Ti content in Ti-based metallic glasses would benefit their specific strength, developing Ti-based bulk metallic glasses (BMGs) with high Ti content has drawn great attention of researchers. However, excessive Ti content usually deteriorates their glass forming ability (GFA), especially for Ti-based BMGs with Ti content higher than 50 at.%. Here, based on the Ti55Zr15Be20Ni10 BMG with a critical diameter of 5 mm, the (Ti55Zr15Be20Ni10)100-xFex alloys were designed and investigated. The (Ti55Zr15Be20Ni10)96Fe4 BMG exhibited a critical diameter of 10 mm, suggesting GFA of the Ti55Zr15Be20Ni10 BMG could be improved by Fe addition. In addition, their yield strength increased with Fe addition, thus the specific strength was enhanced from 3.98 × 105 N m/kg to 4.46 × 105 N m/kg, providing the most optimal scheme of specific strength and GFA among the reported Ti-based BMGs. The developed BMGs exhibited high pitting potentials in 3.5 wt.% NaCl aqueous solution, which were 1.8~2.8 times higher than that of 304 stainless steel. The present result shows that the developed Ti-based BMGs containing high Ti content, combined with high specific strength, large glass forming ability and good corrosion resistance, are promising for applications requring lightweight alloys.

Magnesium nanocomposites: An overview on time-dependent plastic (creep) deformation

Abstract Magnesium (Mg) nanocomposites are created when nano-size particles are embedded into the Mg (or Mg alloy) matrix. The Mg nanocomposites, cited as high-strength energy-saving materials of future, are a group of emerging materials with excellent combination of strength and ductility and superior specific strength property (strength-to-weight ratio). Having said this, Mg nanocomposites are considered as promising replacement for other structural alloys (i.e. aluminum and titanium) wherever low density and high strength are required, i.e. transportation, aerospace, defense, etc. To be able to apply this group of materials for real components, different failure mechanisms at ambient and elevated temperatures under static and dynamic loading condition must be well documented. Compared with other metals and alloys, rate-dependent plastic deformation (creep), at ambient and elevated temperatures, of these novel materials is not yet well studied which seems a tangible lack of knowledge. This is required since the materials in service are often exposed to medium and elevated temperatures and/or static loads for long duration of time and this encourages creep failure on them. To this end, the information and the controlling mechanisms on time/temperature-dependent response of the material need to be developed to be able to predict the response of the Mg nanocomposites where the materials are under creep conditions. This paper aims at providing an overview on (i) creep-resistant Mg alloys (as matrix) and their chemical compositions, and (ii) responses of the Mg nanocomposites at different creep conditions (time and temperature). The controlling mechanisms contributing to the strength and ductility of the Mg nanocomposites due to the presence of the nanoparticles have been reviewed briefly in the present article. In this paper both traditional (uniaxial) and depth-sensing indentation creep of Mg nanocomposites are reviewed. Also, some fundamental questions and possible explanations have been raised on the creep characteristics of Mg nanocomposites and the contribution of microstructural features (i.e. grain boundaries, twins, precipitates, nanoparticles). This overview article provides a comprehensive summary to understand one of the failure modes (creep) at ambient and elevated temperature in the energy saving Mg nanocomposites that would be of interest for those in academia who explore novel nanocomposites.

Hydrophobic Porous Layer By Plasma Electrolytic Oxidation of Magnesium Alloy for Corrosion Resistance

Magnesium and its alloys have aroused significant attention in a wide range of applications, due to their superior dimension stability, thermal conductivity, damping capacity and high specific strength. Nevertheless, the corrosion resistance is a critical issue in the practical application of the magnesium and its alloys, thus various strategies have been introduced to prevent or impede the corrosion of magnesium. Especially, a plasma electrolytic oxidation (PEO), which forms a thick oxide layer, is considered as a promising technology to passivate the magnesium and its alloys. However, the PEO treated surface shows a great wettability to water and corrosive liquid, the corrosion resistance is not sufficient for the practical applications. In this work, we employed a self-assembled monolayer coating on PEO treated surface of magnesium alloy to hydrophobize the porous oxide layer. The hydrophobic coating enabled the porous oxide layer by PEO to retain air within irregular pores, so that the penetration of corrosive liquid toward the magnesium alloy substrate is prevented. Therefore, the hydrophobized porous oxide layer significantly improved the corrosion resistance of magnesium alloy compared to the hydrophilic porous oxide layer absorbing the corrosive liquid easily. Moreover, due to the porous and rough nature of PEO layer, the hydrophobized surface shows a high mobility of water, thus the self-cleaning property can be realized on the surface of magnesium alloy.

High-fidelity non-linear analysis of metal sandwich panels

The considerably superior specific strength and stiffness of sandwich panels in relation to conventional structural components makes their employment for two-way spanning structural applications a highly attractive option. An effective high-fidelity numerical modelling strategy for large-scale metal sandwich panels is presented in this paper, which enables the capturing of the various forms of local buckling and its progression over the panel domain, alongside the effects of material non-linearity and the spread of plasticity. The modelling strategy is further enhanced with a novel domain-partitioning methodology, allowing for scalable parallel processing on high-performance computing distributed memory systems. Partitioned modelling achieves a substantial reduction of the wall-clock time and computing memory demand for extensive non-linear static and dynamic analyses, while further overcoming potential memory bottlenecks encountered when conventional modelling and solution procedures are employed. A comparative evaluation of the speed-up achieved using partitioned modelling, in relation to monolithic models, is conducted for different levels of partitioning. Finally, practical guidance is proposed for establishing the optimal number of partitions offering maximum speed-up, beyond which further partitioning leads to excesses both in the non-linear solution procedure and the communication overhead between parallel processors, with a consequent increase in computing time.

Mechanical behavior of Al-matrix nanocomposites produced by stir casting technique

Aluminium matrix composites (AMCs) have emerged as a material for aircraft and automotive applications owing to its superior specific strength, stiffness, controlled co-efficient of thermal expansion, light weight and excellent wear resistance. The current research study emphases on the production of aluminium (AA6082) matrix composites reinforced in different volume fractions of alumina (50nm) particulates by using stir casting method. The volume fraction of reinforcement was varied from 0% to 3% in stages of 1%. The produced composites were examined by using scanning electron microscope (SEM). Hardness and tensile strength of the composite was studied. The mechanical properties of these composites were compared with matrix alloy. Microstructural results revealed the homogeneous distribution of nano alumina particles in the matrix. The test results revealed that the hardness and tensile strength of the composite increase with an increase in the volume fraction of alumina particle content, this may be due to good interfacial bonding between the reinforcement and the matrix.

A multi-objective design optimization technique for weight and cost minimization of hybrid laminated composite structure by modified non-dominated sorting genetic algorithm

Laminated composite panels are presently being used in wider applications in automotive, aerospace, defence and civil type of industries. It has various advantages over conventional materials with superior specific stiffness & strength, fatigue and corrosion resistance with energy absorption feature comparing others. Optimal design of composite laminates regarding change in ply angles to increase the strength is obligatory to realize the complete potentiality of fibre reinforced particles/materials. The above epistemology is applied to the multi-objective design optimization technique of fibre-reinforced solid rocket motor composite cylindrical skirt of space vehicle is analyzed. In that solid rocket motor, a skirt is defined as a feasible component for weight diminution which leads to reduction of entire weight. Due to its significance, it is recommended to optimize the both weight and expense of the fibre reinforced composite (FRC) cylindrical shape skirt affected to overstressing strength and buckling strength at the combined conditions of aerodynamic torque and thrust in axial direction. In this paper, the failure principle of Tsai-wu is applied to determine the first ply catastrophe. Failure strength and Buckling strength of the skirt is depicts by using overstressing load level factor and buckling load factor. Various material combinations such as Graphite/Epoxy & Glass/Epoxy, have been used to find the optimal values. Laminated composite skirts are fabricated with glass-epoxy if cost is the criteria and graphite-epoxy if weight comes into an account

High‐Entropy Alloy (HEA)‐Coated Nanolattice Structures and Their Mechanical Properties

Nanolattice structure fabricated by two‐photon lithography (TPL) is a coupling of size‐dependent mechanical properties at micro/nano‐scale with structural geometry responses in wide applications of scalable micro/nano‐manufacturing. In this work, three‐dimensional (3D) polymeric nanolattices are initially fabricated using TPL, then conformably coated with an 80 nm thick high‐entropy alloy (HEA) thin film (CoCrFeNiAl0.3) via physical vapor deposition (PVD). 3D atomic‐probe tomography (APT) reveals the homogeneous element distribution in the synthesized HEA film deposited on the substrate. Mechanical properties of the obtained composite architectures are investigated via in situ scanning electron microscope (SEM) compression test, as well as finite element method (FEM) at the relevant length scales. The presented HEA‐coated nanolattice encouragingly not only exhibits superior compressive specific strength of ≈0.032 MPa kg−1 m3 with density well below 1000 kg m−3, but also shows good compression ductility due to its composite nature. This concept of combining HEA with polymer lattice structures demonstrates the potential of fabricating novel architected metamaterials with tunable mechanical properties.

Static Strength of Adhesively-bonded Woven Fabric Kenaf Composite Plates

Natural fibers are potentially used as reinforcing materials and combined with epoxy resin as matrix system to form a superior specific strength (or stiffness) materials known as composite materials. The advantages of implementing natural fibers such as kenaf fibers are renewable, less hazardous during fabrication and handling process; and relatively cheap compared to synthetic fibers. The aim of current work is to conduct a parametric study on static strength of adhesively bonded woven fabric kenaf composite plates. Fabrication of composite panels were conducted using hand lay-up techniques, with variation of stacking sequence, over-lap length, joint types and lay-up types as identified in testing series. Quasi-static testing was carried out using mechanical testing following code of practice. Load-displacement profiles were analyzed to study its structural response prior to ultimate failures. It was found that cross-ply lay-up demonstrates better static strength compared to quasi-isotropic lay-up counterparts due to larger volume of 0° plies exhibited in cross-ply lay-up. Consequently, larger overlap length gives better joining strength, as expected, however this promotes to weight penalty in the joining structure. Most samples showed failures within adhesive region known as cohesive failure modes, however, few sample demonstrated interface failure. Good correlations of parametric study were found and discussed in the respective section.

Early Damage Detection in Composites by Distributed Strain and Acoustic Event Monitoring

Advances in the development of fibre reinforced polymer composites and their manufacturing techniques have led to their increased use as structural materials. They offer superior corrosion resistance and high specific strength and stiffness, compared to metals, while designing anisotropic structures can provide weight reductions. However, there is uncertainty associated with understanding the consequences of out-of-plane damage in composites. Non-destructive evaluation techniques are adopted in many cases, but represent significant down-time and labour costs. Attached and/or embedded structural health monitoring systems have shown promise in improving the reliability and safety of composites, while reducing lifecycle costs, and improving design and manufacture processes. In this work, a distributed optical fibre sensor is embedded in a six ply carbon fibre-epoxy composite laminate during fabrication, to give three strain sensing regions near the top, middle, and bottom surface of the laminate, which allow in-situ and real time monitoring of strain development in the panel during resin infusion and curing. Four point bending is then conducted on the plate. Acoustic emission events are collected using four bonded piezoelectric wafer active sensors, thus allowing the comparison of strain data with damage formation and growth during progressive loading cycles. Distributed strain data demonstrates the sensitivity of the optical fibre through-the-thickness of the panel. The top, middle, and bottom sensing regions clearly indicate the development of compressive, neutral, and tensile strain, respectively. The strain values obtained from the optical fibre are in good agreement with strain data collected by surface mounted strain gauges. Acoustic event detection suggests the formation of matrix (resin) cracks, with measured damage event amplitudes in agreement with values reported in published literature on the subject.

Improvement of interlaminar fracture toughness in carbon fiber/epoxy composites with carbon nanotubes/polysulfone interleaves

Carbon fiber/epoxy (CF/EP) composites have been widely used as structural materials in many aerospace applications owing to their superior specific strength and specific elastic modulus. However, interlaminar delamination, the most common failure mode of these composite materials, often occurs due to the inherent brittleness of the epoxy matrix. In this study, a vacuum filtration method was used to fabricate sandwiched carbon nanotubes/polysulfone nanofiber (CNTs/PSF) paper as an interleaf to improve the interlaminar fracture toughness of CF/EP composite laminates. During curing of the epoxy resin, the PSF nanofibers were first dissolved and then phase separated from the continuous epoxy matrix to form microspheres while the CNTs were dispersed homogeneously in the epoxy. It was found that interleaving the laminates with the sandwiched paper increased both mode I and mode II interlaminar toughness. Also, the CNTs/PSF interleaved laminates displayed an increase in flexural strength and flexural modulus owing to the reinforcing effect of the CNTs. DMA tests confirmed that better compatibility between PSF and epoxy could be achieved by adding CNTs. The mechanisms for the simultaneous improvements of toughness and flexural properties were analysed.

Experimental Investigation and Optimization in Rotary Ultrasonic Drilling of C/C Composites

C/C composites are widely used in aviation and aerospace due to their low density, superior specific strength, special elastic modulus at elevated temperatures, small thermal expansion coefficient and high fracture toughness. However, there are numerous problems such as delamination, chipping, poor machining quality and tool wear in drilling of C/C composites due to inhomogeneous, anisotropic, wear resistance and varying thermal properties of the composites. In this paper, related experiments on rotary ultrasonic drilling of C/C composites using diamond core drill were conducted to compare the drilling force and machining quality of ultrasonic drilling with conventional drilling, analyze the rotary ultrasonic drilling mechanism and research the influence of spindle speed, feed rate and ultrasonic amplitude on the drilling force. Experimental results showed that rotary ultrasonic drilling can significantly improve the removal of the chips thus preventing the core drill blockage, effectively reduce the drilling force and improve processing quality. In addition, the drilling force decreased with increasing of spindle speed and ultrasonic amplitude, while it increased with increasing of feed rate. Finally, the cutting parameters were optimized by consideration of the drilling force and efficiency.

EVALUATION OF ENERGY RELEASE RATE FOR MODE 1 CRACK PROPRAGATION IN GLASS/EPOXY COMPOSITE

Composite resources are replacing regular engineering metals along with alloys for several applications. Their superior specific strength and stiffness characteristics have made them very competitive in the aerospace industry. The primary limitation of fiber reinforced composites is fracture toughness, specifically delamination. Delamination failures are common due to the nature of composite construction. A variety of manufacturing techniques are available to make composites. Generally, all these methods employ a layered stacking of fibers in a primary plane. The interface between these layers is typically not reinforced with fibers and is the source of delamination or interlaminar fracture. Porosity and Other manufacturing related defects also introduce nucleation sites for delamination. Methods exist to evaluate and quantify inter-laminar fracture toughness, both experimentally and analytically. The material property that best represents resistance to delamination is the strain energy release rate (G C). This can be experimentally obtained and numerically predicted with some success. The primary focus of this study was to characterize and address interlaminar fracture in composites. An interlaminar fracture for mode I crack propagation was analysed for GFRP materials having 0 0 orientation of fibres. Experimental investigation of GC was done for 40%, 50% and 60% of fibre volume. Test was conducted using Double Cantilever Beam specimen. Results obtained were again correlated with Numerical analysis using VCCT method. Results of both experimental and numerical methods were in good agreement.

Fabrication of a Glass‐Ceramic‐to‐Metal Seal Between Ti–6Al–4V and a Strontium Boroaluminate Glass

Glass‐ceramics are widely utilized in the electronics industry to provide electrical insulation and to form leak‐tight joints with a range of metals. The coefficient of thermal expansion (CTE) of the glass‐ceramic can be controlled by the extent of crystallization to reduce detrimental tensile stresses in the joint. In recent years, there has been interest in using titanium alloys, in place of stainless steels, due to their lower density and superior specific strength. In this study, the heat treatment of a strontium boroaluminate glass has been tailored to create glass‐ceramics with mean CTEs ranging from 5.7 ± 0.1 × 10−6/K to 9.7 ± 0.1 × 10−6/K over the temperature range 303–693 K. The resultant glass‐ceramic consists of three crystalline phases and residual glass. A glass‐ceramic with a mean CTE of 6.9 ± 0.1 × 10−6/K was subsequently fabricated to form a compression seal with a Ti–6Al–4V housing and a preoxidized Kovar pin. Single pin assemblies were shown to be reproducible in terms of microstructure and all passed a standard helium leak test, indicating that a successful seal had been produced.

Predicting Impact Damage, Residual Strength and Crashworthiness of Composite Structures

Copyright © 2016 SAE International. The development of the latest generation of wide-body carbon-fibre composite passenger aircraft has heralded a new era in the utilisation of these materials. The premise of superior specific strength and stiffness, corrosion and fatigue resistance, is tempered by high development costs, slow production rates and lengthy and expensive certification programmes. Substantial effort is currently being directed towards the development of new modelling and simulation tools, at all levels of the development cycle, to mitigate these shortcomings. One of the primary challenges is to reduce the extent of physical testing, in the certification process, by adopting a ‘certification by simulation’ approach. In essence, this aspirational objective requires the ability to reliably predict the evolution and progression of damage in composites. The aerospace industry has been at the forefront of developing advanced composites modelling tools. As the automotive industry transitions towards the increased use of composites in mass-produced vehicles, similar challenges in the modelling of composites will need to be addressed, particularly in the reliable prediction of crashworthiness. While thermoset composites have dominated the aerospace industry, thermoplastics composites are likely to emerge as the preferred solution for meeting the high-volume production demands of passenger road vehicles. This keynote paper outlines recent progress and current challenges in the development of finite-element-based predictive modelling tools for capturing impact damage, residual strength and energy absorption capacity of thermoset and thermoplastic composites for crashworthiness assessments.