Proceedings of the Institution of Mechanical Engineers,Part L: Journal of Materials: Design and Applications

Gypsum is one of the most environmentally friendly binders and consequently its importance in building industry is increasing. New applications are being sought and new materials are being developed. A lightweight gypsum material foamed by waste stone dust was designed and tested. The amount of stone dust, a waste product formed during the cutting and polishing of decorative stones, is becoming serious problem in some countries. When the stone dust contains calcium carbonate, it can be used for gypsum foaming to produce cheap, environmentally attractive material. The physical and mechanical properties of lightweight gypsum-based materials with different amounts of stone dust were designed and tested. The material with largest amount of waste stone dust attained a bulk density under 600 kg/m³ and compressive strength of 1.1 MPa, with a thermal conductivity of 0.117 W/m.K. These properties are sufficient for use of the material as a thermal insulating plaster, as the core of thermal insulating gypsum boards or in lightweight blocks for inner walls and partitions. Life cycle cost analyses was performed for the most favourable material and was compared with aerated autoclaved concrete, which is a common commercial product with similar properties.

The article presents the results of “in situ” tests of two new cement mortar floors that were made defectively in an important public building with a large area. The performed results of organoleptic tests and extensive strength tests, which are helpful in determining the causes of numerous and various defects in floors, were presented. It was observed that the source of the aforementioned causes is not only the failure to comply with the technological and technical conditions and requirements for laying a cement mortar mix and the execution of floors but also the lack of appropriate supervision over the entire flooring process. The causes of defects were determined and should help to avoid similar situations in the future.

Juglone is a naphthoquinone-type dye. It is also known as a C.I Natural Brown 7 dye and is used to dye natural and synthetic fibers. This article presents the possibility of using juglone as a natural colorant for biodegradable polymers (polylactide and polyhydroxybutyrate). Based on the results of the research, it was shown that juglone added to biodegradable aliphatic polyesters does not change the properties of the polymers, such as mechanical properties and thermal stability. Noteworthy is the change in the color of the materials under the influence of various external factors, such as temperature, humidity, and UV radiation. Juglone can be used as an indicator of the aging time of polymeric materials. The presented materials, made of biodegradable polymers with a dye of plant origins, may potentially be applied to packaging materials with controllable life-times. The scientific novelty of this paper is the use of juglone as a natural dye and as an indicator of the aging time of biodegradable polyesters (polylactide and polyhydroxybutyrate).

Thermoplastics, such as the polypropylene, often have different behaviours when subjected to traction or compression loads. Thermoplastics are also used in additive manufacturing processes, such as the fused filament fabrication, allowing to build complex structures possessing structural elements with an intricate internal architecture (foams and functionally graded material deposition). Thus, yield criterions have to be appropriately chosen in order to capture the homogenised material non-linear behaviour. In this work, polypropylene regular specimens are discretised and analysed assuming traction and compression tests. The non-linear elastoplastic analyses are performed considering three distinct discrete numerical approaches. Thus, the stress–strain curves obtained using two different meshless methods and the finite element method are compared with experimental data. In the end, a comparative study is performed between the results obtained using meshless methods and the finite element method, and the accuracy of the meshless methods is demonstrated.

Aluminum metal matrix composites, which exhibit significantly high compressive strength, were produced through the squeeze casting process using aluminum 7075 alloy as the matrix material and 2.5 wt% alumina as reinforcement. The process parameters of squeeze casting were prudently selected based on the literature in order to obtain better mechanical properties such as compressive strength and hardness. Samples were examined using an optical microscope, energy dispersive spectroscopy, a scanning electron microscope, and X-ray diffraction analysis. The optical micrograph showed low porosity in the produced composite, which matched the porosity measured using the Archimedes principle. The scanning electron microscope showed uniform distribution of reinforcement in the grain boundaries of the matrix. An X-ray diffraction analysis confirmed the presence of Al₂O₃ particles in the composite. The hardness of the composite improved from 44 to 59 HRB. The compressive strength of the composite improved significantly with the addition of alumina reinforcement to 587 MPa when compared to Al 7075 alloy as well as other aluminum metal matrix composites reported in the literature.

Sandwich panels with aluminum or glass fiber composite facesheets and polyurethane or polystyrene foam core were tested in impact by using an Instron Ceast 9340 impact tower at speeds from 1.5 to 4.5 m/s. The influence of the initial velocity of impact and kinetic energy is analyzed for all types of panels. Particularities of the impact response of the sandwich panels were observed and explained. The facesheet type influence on the damage and penetration of the panels during impact is discussed. If the absorbed energy of the panels is a priority, then the aluminum facesheets and the polystyrene foam core are a good combination. If minimum deformation is required, then composite facesheets and the more rigid polyurethane foam core are a strong option for the sandwich panel design.

Fiber-reinforced polymer composites yield a range of microscopic damage mechanisms even under apparently “simple” load cases, e.g. quasi-static uniaxial tensile tests to failure. Even reducing the fiber-reinforced polymer composite to a single fiber embedded in a matrix will produce several different damage types under quasi-static tensile loading. These are fiber breaks and simultaneous fiber–matrix debonding as well as friction between fiber and debonded matrix, and sometimes, additional matrix cracks. Acoustic emission monitoring of mechanical load tests on material specimens or components is often used to identify the occurrence of damage and attempts at locating the source and identifying the damage mechanism or type in a wide range of materials. The complex damage behavior of fiber-reinforced polymer composites poses a challenge in that respect. Therefore, various approaches (e.g. pattern recognition or neural networks) have been developed to identify the different microscopic damage mechanisms from acoustic emission signals obtained from various load tests. For improved understanding of the damage mechanisms in fiber-reinforced polymer composites as well as for validating the procedures for identifying the types of mechanisms, fiber-reinforced polymer specimens showing a “single dominant damage mechanism”, i.e. occurring in significantly larger number than all others, at least in certain stages of damage accumulation or in localized volume elements, can be designed. The contribution discusses and classifies selected examples of single dominant damage mechanism for fiber-reinforced polymer composites and their application.

Composite sandwich materials are very common in structural uses for a wide range of applications in the aerospace and automotive industry that require low weight, high bending strength, and high energy absorption. In general, the core of the sandwich structures has a two-dimensional cellular structure, with a regular honeycomb geometry. While with standard manufacturing processes the geometric structures are limited, the emergence of additive manufacturing provides alternatives to conventional designs. The aim of this work is to analyze and evaluate the effect of the core geometry on the flexural properties of the structure. For that purpose, three different cellular configurations were considered, namely regular honeycombs, lotus, and hexagonal honeycombs with Plateau borders. Four relative densities, with average values of 0.1, 0.25, 0.44, and 0.62, for each configuration, were studied. The flexural properties of cellular structures were evaluated with three-point bending tests, both numerically and experimentally. A modeling approach of the tests in the three configurations was performed, for two materials, polylactic acid and pure aluminum, by means of finite element simulations. Fused deposition modeling was used to obtain polylactic acid samples for the aforementioned configurations, which were experimentally tested to evaluate the mechanical response and the failure behavior of the cores. Results differ with the geometry arrangement and showed a strong dependency with the relative density of the structures in the flexural response in what concerns strength, stiffness, and energy absorbed. The arrangements studied present properties, which make them competitive with the traditional core structures for the same density. A promising agreement between experimental and simulation results was obtained.

In this work, a numerical–experimental study of the interlaminar zone for an unidirectional glass fiber reinforced epoxy composite is carried out in order to predict the load–displacement curves of a double cantilever beam test. First, an experimental mechanical characterization of the laminated composite was made through quasi-static in-plane tensile and bending tests and out-of-plane delamination tests (i.e. double cantilever beam tests or opening mode I). The main results have shown that the elastic module in the fiber direction is E₁ = 32.1 GPa and the fracture process is characterized by a critical energy release rate G _IC  = 1466 N/m. In order to be able to predict delamination using finite element analysis, a bilinear cohesive zone model is adopted. This law has two parameters—the initial stiffness K ∼ and the critical traction t n 0 —to be fit for reducing the distance between numerical and experimental double cantilever beam load–displacement curves. That means an optimization problem, which is here solved by proposing a very simple and cheap three-step procedure, avoiding expensive three-dimensional simulations: (i) the numerical double cantilever beam test is coded in the OCTAVE software using one-dimensional beam elements and the bilinear cohesive zone model; (ii) several one-dimensional simulations are performed varying at the cohesive law's parameters in order to build the objective function; and (iii) a genetic algorithm from the Scilab optimization toolbox is then used to determine the interface's parameters minimizing the objective function. This method has proposed K ∼  = 2.74 × 10¹⁴ N/m³ and t n 0  = 1.99 MPa as the best parameters fitting the curves. Finally, the identified bilinear cohesive law's parameters are used to carry out a full three-dimensional finite element analysis simulation in ANSYS, showing the same response than the simplified beam code, but with the possibility to obtain more accurate information about the fracture process (e.g. the shape of the process zone) or to use more complicated geometries or boundary conditions. In this work, we show the ability to predict the material behavior through different methods, using the best characteristics of each one.

This paper focuses on the development of a new mathematical model and its analytical solution for the analysis of the mechanical behavior of geometrically and materially linear three-dimensional two-layer bimetallic beams with interface compliance. Consequently, the analytical solution of bending of elastic three-dimensional two-layer composite beams with interface compliance is derived for the first time. In the illustrative example, a three-dimensional two-layer cantilever composite beam made of 6061-T6 aluminum and C83400 red brass is analyzed. It is shown that interface compliance could have a significant influence on the mechanical behavior of such a structure. Finally, the results for different mechanical quantities are tabulated and as such the analytical solution presented can be used as a benchmark solution of three-dimensional bimetallic composite beams.

This study addresses the effects of roughness anisotropy in the tribological behavior of AA5083. Wear tests were carried out using a reciprocating tribometer under a contact pressure of 200 MPa. Sliding was performed on three topographic orientations. The friction force was recorded instantaneously. Furthermore, microscopic analyses were conducted for the purpose of characterizing the wear mechanisms. The findings proved the sensitivity of friction and wear of the initial surface properties. A numerical model of the reciprocated test was, in addition, developed upon ABAQUS/Explicit to better understand the evolution of equivalent plastic deformation during sliding. The proposed model is able to simulate a real surface profile described using python scripts. The model was found very useful in highlighting the significant effect of surface anisotropy on the stress distribution and plastic deformation.

Orthopedic surgeons frequently face the problem of selecting adequate implants that fulfill certain characteristics of mechanical stability and biological features. Recent three-dimensional printing advancements have made possible the use of biologically compatible materials in regenerative medicine in order to meet the increasing demand of tissue and organs, including bones. Current three-dimensional printing bone technologies can create either strong bone structures (based on primary scaffolds) that are structurally compatible but functionally inert or structures that have osteoconductive properties but are extremely weak. In this context, the present article presents a follow-up study based on previous analysis in which a new technique is used to create high-resistance implants using biocompatible materials as acrylonitrile butadiene styrene to print biomimetic scaffolds directly from computer assisted design data. The main objective is to develop a design methodology to model and create artificial bone tissue, based on the trabecular pattern of the host, to obtain scaffolds within a structural design that mimics the mechanical resistance of the patients’ bone. These scaffolds, obtained from a micro-tomography, would generate stronger structures by enhancing them with osteoblast precursor cells in an osteogenic habitat in order to generate bone tissue in their surface. Mechanical strength of these scaffolds is also analyzed by comparing models with and without trabecular patterns using a standard compression test. The anisotropy of the structures was also considered in this analysis. Results confirm that trabecular pattern and bone matrix formation enhances the mechanical strength of the scaffolds obtaining similar values as of real trabecular tissue. The clinical use of the developed structures would constitute a new generation of three-dimensional-printed functional implants.

The main objective of this paper is to investigate material flow and force requirement in sheet-bulk forming processes where loading is applied perpendicular to sheet thickness. The presentation draws from material characterization to experimental and numerical analysis of process parameters related to the material and geometry of the blanks, and to the shape of the forming punches. The work is performed in aluminum AA-5754-H111 and polycarbonate and is a step towards exploring the potential of using sheet-bulk forming to produce polymer parts at room temperature. Incremental sheet-bulk forming of polymer rack gears demonstrate the potential of the process to fabricate small batches of complicate parts widely used in machines and mechanisms.

Despite extensive research regarding metal cutting simulation, the current industrial practice very often relies on empirical data when it comes to tool design. In order accurately simulate the cutting process it is not only important to have robust numerical models that closely portray the phenomenon, but also to properly characterize the material taking into account the cutting conditions. The goal of this investigation focuses on the mechanical characterization of the cast aluminum alloy AlSi₉Cu₃ by conducting both compression and fracture tests. Due to its very good castability, machinability, and attractive mechanical properties, this alloy is widely used in casting industry for the manufacture of automotive components, among others. Besides the experimental characterization, a numerical methodology is proposed for the modeling of the cast alloy, making use of the Johnson–Cook constitutive material model, in Abaqus/CAE. The material model is calibrated based on compression tests at multiple conditions (quasi-static, incremental dynamic and high temperatures). The identified model is then validated by simulation of the ductile fracture tests of notched specimens. The obtained numerical results were consistent with the experimentally obtained, contributing to the validity of the presented characterization technique.

Significant improvement in formability of aluminum alloys can be obtained when these materials are formed in the warm working temperature range (below recrystallization temperature). In the present work, an experimental set up is designed and developed to determine formability of Al–Mg–Si alloy (AA 6061) sheets of different thickness in the temperature range of 200–300 ℃. It consists of lower and upper dies with casing heaters, a hemispherical bottom punch with heating element, controls for punch displacement and speed of the 60-ton double action hydraulic press used in the experiments. An attempt has been made to experimentally determine the influence of punch speed, temperature, and sheet thickness on the limiting dome height and forming limit diagram in the warm working temperature range. The effect of temperature and strain rate on tensile properties of the alloy has also been studied. The plane strain intercept values of forming limit diagram (FLD₀ which is the major strain value at zero minor strain), determined experimentally at different conditions and thicknesses, have been used to develop a correlation for FLD₀ with temperature, punch speed and thickness. The FLD₀ values obtained from the developed correlation agreed well with the experimental values with the difference less than 10% in most cases. The confirmatory experiments at an intermediate punch speed showed an error of just 8%. The effect of temperature and punch speed on strain distribution in the forming limit diagram samples and the load–displacement curves has also been analyzed.

Titanium aluminides are used in the aeronautical and automotive field as an alternative material to manufacture critical components exposed to high temperatures and corrosive environments. These alloys due to its intermetallic structure exhibit some special properties such as low density, high strength, high stiffness, corrosion resistance, and creep resistance. When these components are manufactured, surface integrity is one of the most relevant parameters used to evaluate the quality of the parts. Severe surface integrity problems are reported in the literature, defects such as microstructural alterations, work hardening, residual stresses, surface cracks, among others induced by the cutting process. The surface and sub-surface alteration induced by machining are critical because it will affect the parts performance. Some parameters affect the quality of machined surface. In particular cutting parameters, cutting tools material, tool wear and material properties are the most frequently investigated. Experimental and empirical studies are presented mainly in order to understand the surface integrity induced by machining. This paper provides an overview of the problems associated with the machining process of various types of titanium aluminides. The cutting tools, machining parameters, as well as processing parameters employed to improve machinability and reduce surface defects in titanium aluminides are analyzed and discussed. Particular focus was given to turning and milling process of gamma titanium aluminides. Also, some of the optimal parameters for machining titanium aluminides are presented offering a compilation of the most relevant information from the first to the most recent works that analyze the different aspects that affect the machining of these alloys.

Adhesive bonding is extensively used by several industries. A large number of joint architectures are available, of which the most typical ones are single-lap, double-lap and scarf joints, each one with their own benefits and limitations. Bonded joints are also widely used to join tubular components in the pipeline industry (petroleum production, energy and wastewater treatment), in vehicle frames (aeroplanes, cars and buses), in civil engineering truss structures and in space structures. This joint design is mainly subjected either to axial or torsional loads. For the design process of these joints, analytical or numerical predictive techniques can be used. This work performs a comprehensive experimental and numerical study of axially loaded tubular joints between aluminium adherends and bonded with three different adhesives. The effect of the overlap length between inner and outer tubes (L_O) was addressed in the experiments and numerical study. A conventional continuum-based finite element method analysis was undertaken to analyse peel (σ) and shear stresses (τ) in the adhesive layer. Cohesive zone models were subsequently employed to perform a damage evolution analysis and to predict the joint strength. A comparison between axisymmetric two-dimensional and full three-dimensional simulations was undertaken. The cohesive zone model technique was positively validated for the strength analysis of tubular joints. It was also shown that the joints' geometry and type of adhesive highly influenced the joints' behaviour.

The potential of an electrospun nylon nanofibrous mat as adhesive carrier and reinforcing web in adhesive bonding has been proven by the authors in a previous work. In that work, a pre-preg nanomat was developed using a low-viscosity epoxy resin for composite hand lay-up, in order to favour wetting of the nanofibres and to minimize air entrapment. However, the resin for hand lay-up exhibited a poor bonding performance when compared to the one typical of epoxy adhesives. The present work is therefore aimed at developing a laboratory route to add an electrospun polymeric nanomat to a two-part epoxy adhesive joint. Three different adhesives with increasing viscosity have been preliminarily evaluated regarding the entrapment of air after curing. The most promising one has been used to manufacture a small-size, Al-alloy double cantilever beam joint and compare the performance with and without the nanomat. Three different precracking procedures have also been developed and evaluated, namely fatigue precracking (A), razor blade tapping (B) and nanomat exfoliation (C). The results indicate that the fracture toughness of the nanomat-reinforced adhesive joint is similar to the neat adhesive one at the beginning of the propagation but it becomes much higher as the crack advances.

A laser transmission-based joining process is investigated, joining one thermoplastic adherend (PA6) which is transparent for the applied laser radiation with another adherend being a thermoset carbon fiber-reinforced plastic. The application is addressed to use thermoplastic fasteners to join different materials to thermoset carbon fiber-reinforced plastic parts. The influence of different laser intensities and different amounts of introduced energies to the joint are investigated. Therefore, laser parameters such as scan speed and laser power are varied using a fiber laser and a scanner optic. The same laser source is used to pretreat the thermoset surface exposing the C-fibers before joining. The performance and the quality of the joints are evaluated by mechanical shear-tests and microscopic cross sections. The results show the significant influence of laser intensity and energy on damage-mechanisms but also the possibility to provide good quality joints reaching up to 13.8 MPa.

The number of electric and hybrid vehicles on the roads has increased significantly in recent years. The high weight of these vehicles requires the use of lightweight construction technologies and materials. In this context, adhesively bonded multi-material structures are increasingly being used. However, the combination of different materials with the production processes established in the automotive industry is a challenge to the manufacturers. Especially the drying process after cataphoretic dip coating can lead to adhesive failure. In order to detect and solve these problems as early as possible, a forecast using the finite element simulation is necessary in the early stage of the project. The objective is to show that a temperature-dependent cohesive zone model can be used to predict damage during the drying process. Therefore, the parameters for such a model were identified on different temperature levels using tubular butt joints, tapered double cantilever beams, and tapered end notched flexure specimens. Finally, the material model was validated on heated lap shear specimens. It could be shown that it is generally possible to predict damage within the adhesive layer using a cohesive zone model. Furthermore, it was shown that the way the stiffnesses are determined has a decisive influence on the calculation accuracy under temperature influence.

In many plastics engineering applications, fastenings are typically realized by means of snap fits instead of conventional types of fasteners such as screwed fits or rivets. Snap fits can be easily integrated into injection molded parts and enables later assembly without additional fasteners. When disassembling a ring-type snap fit, the viscous deformation resulting from the hysteresis behavior of the polymeric material can reduce the holding force and the disassembly force. In a conventional finite element analysis of the assembly and disassembly process, the hysteresis behavior is usually not taken into account. After loading and unloading a part, a permanent set after the removal of the load is found, which is due to the viscous material deformation of the polymeric material and yields the accompanying change in deformation behavior under sequence of loading procedures. The first assembly can already lead to mechanical damage of the polymeric part. Consequently, in return it explains why the disassembly forces of a ring-type snap fit are lower than the assembly forces. The reduction of the necessary disassembly force due to mechanical damage reaction needs to be predicted by a simulation of the component. Therefore, the different deformation behavior during assembly and disassembly of the snap fit, which in turn is influenced by the height of the deformation of the snap-in element during assembly, must be taken into account for a simulation. Neglecting to observe this different deformation behavior can result into a malfunction or even failure of the component during application may occur. The simulation possibilities for deformation behavior during force loading and unloading of a polymeric joint is investigated by means of finite element analysis. The assembly and disassembly forces of a ring-type snap fit made of polyoxymethylene were simulated employing three different material constitutive models and compared with experimentally measured results. For the simulation of a subsequent disassembly and further assembly, only a viscoelastic material model satisfactorily predicts the measured behavior of the component in the experiment.

The state of the surface plays a crucial role in defining the mechanical properties of bonded joints, in particular, the chemical state of the adherend surface and its structural morphology have been proved to be the main elements of the bonding process. The structural morphology of the surface strictly depends from its topological features, like roughness, presence and distribution of grooves, homogeneity, etc. In a previous work, the effect provided by pulsed Yb-laser ablation on the mode I energy release rate of aluminium double cantilever beam joints was evaluated, in order to identify a relation between the combination of laser parameters and the morphological characteristics of the ablated surfaces which can support in identifying the optimal process configuration. The experimental tests showed that the fracture toughness of the double cantilever beam joints grew up as the surface roughness increased until a threshold value, after which the grooves resulted too narrow to allow the adhesive to completely fill them, inducing a higher amount of entrapped air into the grooves and therefore reducing the level of failure propagation energy. In this work, the problem dealing with the influence that the presence of air bubbles has over the mechanical behaviour of bonded joints was considered and the study went deeper into the investigation on the relation between laser-induced surface topology and mechanical response of joints. Different surface textures involving different directions and conditions of treatment were realized and their effect on the mechanical properties of aluminium bonded specimens was evaluated through experimental tests. The characterization of the treated surfaces was carried out by observing them with a 3D optical profiler and with SEM analysis and by measuring some geometrical features of the patterns created as a result of laser ablation.

The use of bonding for joining composite materials in high-performance structures has increased significantly, as this joining method offers improved stress distributions and capability of joining dissimilar materials. However, the use of adhesive bonding for this purpose might lead to delamination failure, caused by peel stresses acting on the generally weaker transverse direction of the composite adherends. This work focused on improving the resistance to delamination of composite adhesive joints by using a novel composite with a reinforced high toughness resin on the surfaces. Single-lap joints using the novel composite material as adherends, were found to have 22% higher failure loads when compared with the specimens using carbon fiber reinforced polymer only adherends, with the failure mode changing from delamination of the adherends to cohesive failure in the adhesive. The lap shear strength was also close to that attained when using high strength steel adherends. A finite element analysis, using cohesive elements, was performed with the objective of reproducing the experimental results and better understanding the failure mechanism. Using this model, it has been determined that the change of failure mode and the plasticity on the surface layers are the two key factors underlying the increase in strength obtained with the novel adherends.

Dissimilar welding of 2024Al alloy to SiC/2009Al composite was conducted via solid-state ultrasonic spot welding technique. Defect-free sound spot welds were successfully achieved. SiCp particles were observed to migrate from the composite side to 2024Al side along with the interfacial interlocking during the intense high-frequency rubbing, which increased with increasing welding energy. The microhardness across the ultrasonic spot welded similar and dissimilar joints remained nearly constant. The tensile lap shear failure load increased with increasing welding energy, and satisfied the requirements of AWS standard D17.2 for spot welding. In addition to room temperature tensile lap shear tests, all the similar and dissimilar joints were subjected to tensile tests at varying temperatures and their respective results were discussed.