Materials Design and Applications IV

In this work, a novel Mg-Zn-Ca-Er alloy was prepared. A spark plasma sintering (SPS) technique was used to produce samples from powders synthesized by mechanical alloying (MA). Sintering temperature of 583 K and holding time of 4 min were used. These parameters allow to obtain the appropriate densification and compaction in the produced samples. Before and after sintering, microstructural changes were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The results of density measurements, microhardness, and compression strength tests are presented. Analyses showed that amorphous structure was achieved by mechanical alloying for milling times exceeding 20 h. A substantial increase in hardness values with increasing the milling time up to 70 h was attributed to the particle size decrease, and strong plastic deformations occur. The mechanical properties that can be achieved using SPS of the Mg-Zn-Ca-Er alloy are promising. Mechanical test results displayed reasonable improvements in compressive strength with decreasing porosity of the samples. Fracture morphology of the Mg-Zn-Ca-Er is the characteristic for brittle crystalline materials.

The human behaviour has significantly affected the climate. Because of that, the pursue of new alternatives for non-renewable materials has increased. In that scenario, the use of natural fibre to substitute synthetic ones in composite materials has also increased. In this work, two types of natural fibres from different regions and climates were evaluated and compared. The evaluated fibres were Coir from Brazil and Hop from Portugal and also were evaluated two different extraction methods for the hop batches, boiling in NaOH and maceration in water. To evaluate the composite mechanical characteristics, seven tensile tests were performed in each fibre batch, according to ASTM C 1557-14—Standard Test Method for Tensile Strength and Young’s Modulus of Fibres, and the average tensile strength for each one was calculated. The highest value of ultimate tensile strength was brought by the hop extracted with the boiling in NaOH method and resulted in an average of 16 MPa.

Doors and windows represent a vital role in domestic energy efficiency, and multi-material beams with a thermal break can be fundamental in terms of energetic sustainability. Their static and dynamic structural performance is fundamental to ensure a proper thermal insulation. Two multi-material composite beam topologies were tested in a three-point bending, while one was subjected to an experimental frequency response analysis. FEM models were created for the composite beams, using beam elements (BEAM189) and solid elements (SOLID186) with a shared topology configuration. Their capacity to predict the static and dynamic behaviour of the beams was assessed by comparing the numerical results with the experimental and analytical data. It is shown that the three-point bending behaviour of the physical beam could not be realistically captured by the 1D beam elements model, as their cross section with different components could not be coupled due to the relatively low stiffness of the polymeric components. However, the eigenfrequencies from the beam elements were very close to those measured experimentally, meaning the dynamic modulus at low strain values could keep the beam’s cross section in-plane during the experiment. On the other hand, the 3D solid elements had the opposite outcome, agreeing with the experimental three-point bending test but not with the experimental modal analysis.

The aim of the study was to design a cementitious material that is prepared with the synergistic addition of sodium silicate and granite fine aggregate in order to obtain low capillary suction. For this purpose, three different classes of cement mortar (M15, M10, M5), one type of granite fine aggregate and two different proportions of additive in the form of sodium silicate (0.002 kg, 0.005 kg) were analysed. Firstly, the capillary suction of the granite aggregates was analysed and compared with traditional sand. Afterwards, nine cementitious material bars were made, which were then used to examine the capillary suction. It was proved that the M15 cementitious material with the granite fine aggregate and a higher proportion of the additive had the lowest capillary suction. In turn, the M5 cementitious material without the additive had the highest index of capillary suction, which shows that adding sodium silicate to cement mortar can significantly reduce its capillary suction. Finally, the results of this study were compared with the previous authors’ studies concerning basalt and quartz fine aggregates. As a result of the research, it was found that the cementitious material with the fine quartz aggregate had a lower rate of capillary suction index than the cementitious material with the fine basalt aggregate.

The paper presents the possibility of producing foamed geopolymer materials with various foaming agents. Geopolymer is an amorphous aluminosilicate polymer made from the synthesis of silicon (Si) and aluminum (Al), geologically obtained from minerals. Geopolymers contain long chains (copolymers) of aluminum–silicon and aluminum, stabilizing metal cations, most often sodium, potassium, lithium or calcium, and bound water, in addition, there are usually various mixed phases: silicon oxide, unreacted aluminosilicate substrate, and—sometimes—crystallized aluminosilicates of the type zeolite. Most methods of geopolymer synthesis come down to one process: The fine and dried pozzolanic materials are mixed with an aqueous solution of a suitable silicate with the addition of a strong base—usually concentrated sodium or potassium hydroxide. The resulting paste behaves like cement. Fly ash from the Heat and Power Plant in Skawina (Poland) was used as a precursor for the production of geopolymer. The activation process was performed with a 10-molar solution of sodium hydroxide NaOH in combination with a solution of sodium silicate. The foaming agents were perhydrol, aluminum powder, and the Sika^® Lightcrete-400 foaming saucer—an organic surfactant for the production of low-emission, lightweight, porous concrete. The produced foamed geopolymer materials were subjected to strength and thermal conductivity tests. The properties of the foams are related to the used foaming agent, but it is not the only factor affecting the quality of the materials. In the production of samples, the crucial factors are mixing the materials, the amount of the added additive, and the temperature of the geopolymerization process.

Fused deposition modelling is an additive manufacturing technique, classified as one of the most popular 3D manufacturing processes, because of its low cost and easy usability, resulting in good quality products. However, the mechanical properties of manufactured pieces depend on the base material properties, manufacturing parameters and room conditions (temperature and moisture). For those reasons, to obtain the optimal conditions, three different types of experimental tests were performed: tensile, flexural and water absorption. These tests were carried out to determine ABS and PLA’s mechanical and physical properties, which are the main materials used in FDM technique. Results showed that PLA has higher values of tensile and flexural strength comparatively to ABS and, in the other hand, ABS had greater weight of water absorption.

Mortars, in particular 3D printing (3DP) ones, rely heavily on Portland cement (PC), a material that entails high carbon emissions and energy consumption related to its manufacture. As its use must become more moderate to comply with the growing environmental regulations and concerns, alternatives to PC or additives to reduce its percentage are being sought. Due to providing adequate pozzolanic activity and filler effect, many supplementary cementitious materials (SCM) have been used, such as agricultural waste. Sugarcane bagasse ash (SCBA) emerges as a strong contender, since sugarcane is available in rich quantities in Brazil and India, with almost no land left to dispose the raw bagasse. The aim of this research is to present a mixture for 3DP with a suitable SCBA content that conforms with the properties in the fresh (flow table and slump) and hardened states (compressive and flexural strength). SCBA with a particle size up to 250 µm was used to replace PC with different dosages (5, 10, 15, 20, 25%), by volume of binder. The fine aggregates used (two types of sand) were kept constant, according to the reference mixture, and no plasticizers or superplasticizers were incorporated. Experimental results showed that an increase in SCBA caused an increase in the water content and the mixture with 5% of SCBA showed similar results of mechanical strength at 28 days when compared to the reference mixture.

Belt–pulley transmissions are a classical topic in mechanical engineering, usually studied following two approaches: the creep theory (Euler or Grashof model) and the shear theory. Recently, the authors introduced a new theory to study the belt–pulley contact mechanics, which is inspired to the brush model used for pneumatic tires. Basing on this theory, the belt is considered as an almost axially rigid tension member connected to a series of bristles, which are, at the other end, in contact with the pulley. In this paper, a test bench is presented and designed to experimentally validate the brush model. The bench is made up of two pulleys connected to two shafts driven by independently controlled motors; a belt is installed between the pulleys, and the shafts are equipped with sensors measuring the angular velocity and the transmitted torque. The belt preload, which is measured by a load cell, can be varied by changing the distance between the two shafts. The belt was painted creating a suitable texture (random speckle pattern) to be interpreted using the Digital Image Correlation (DIC) technique. The first results obtained by carrying out tests at low speed with different transmitted torque values are discussed, appreciating the variation in the tension of the belt along the winding arc and the dependence of the radial compression of the belt from the transmitted torque. The tangential deformation of the belt under the action of different torque values and direction of rotation of the pulleys is also presented, which is consistent with that foreseen by the brush model.

In this study, rubber pad forming is employed for the cost-effective production of metallic bipolar plates. To this end, a punch with parallel serpentine flow field patterns and a rubber layer is used to form SS316 bipolar plates with a thickness of 0.1 mm. The influence of forming force and rubber hardness on the channel depth of the bipolar plates is investigated. Results show a direct relationship between the channel depth and the applied force. The maximum channel depth is decreased by increasing the hardness of the rubber. However, a remarkable reduction in the rubber hardness reduces the system’s performance in supplying the pressure required for forming microchannels and results in an unformed bipolar plate. Thus, to achieve a greater channel depth, the applied force and the rubber hardness should be increased accordingly.

Due to economic and ecological requirements and the associated trend towards lightweight construction, mechanical joining technologies like self-piercing riveting are gaining in importance. In addition, the increase in lightweight multi-material joints has led to the development of many different mechanical joining technologies which can only be applied to join a small number of material combinations. This leads to low process efficiency, and in the case of self-piercing riveting, to a large number of required tool changes. Another approach focuses on reacting to changing boundary conditions as well as the creation of customised joints by using adaptive tools, versatile auxiliary joining parts or modified process kinematics. Therefore, this study investigates the influence of increased die-sided kinematics on joint formation in self-piercing riveting process. The aim is to achieve an improvement of the joint properties by superimposing the punch feed. Furthermore, it is intended to reduce required tool changes due to the improved joint design. The investigations were carried out by means of a 2D-axisymmetric numerical simulation model using the LS-Dyna simulation software. After the validation of the process model, the die was extended to include driven die elements. Using the model, different kinematics as well as their effects on the joint formation and the internal stress concentration could be analysed. In principle, the increased actuator technology enabled an increase of the interlock formation for both pure aluminium and multi-material joints consisting of steel and aluminium. However, the resulting process forces were higher during the process phases of punching and spreading.

During the process of bone fracture fixation and reconstruction surgery, bone screws and or fixation plates are used by surgeons. Preliminary experiment showed that the micro-motion of the bone screw leads to loosening and causes the implant to dislocate from its location. Several experimental procedures such as push-in, pull-out, screwing torque and bending tests are used to evaluate the strength of the screw fixation. Although pull-out tests are widely used by researchers, the interaction between the screw fixation and bone surface is largely unexplored until now. This paper aimed at assessing the screw pull-out using homogenized finite element analysis. Owing to the need for longer computational time, screw threads were not considered in most of the finite element analyses done until now. So, it is unclear how different screw types affect the screw–bone interaction. In this paper, finite element analyses were used to compare different types of the screw–bone interfaces. Analyses were performed using buttress and reverse buttress screws, and then the resulting stress distributions around the bone–screw interfaces were analysed. To resemble the actual scenario, screws were pulled out from the bone considering the physiological loading conditions. The obtained results showed that the influence of screw type on stress distribution in the bone-implant interface is significant. As a conclusion, the use of longer screw rods could provide an increased anchoring effect to the fixation device. However, increasing the number of screws potentially cause the stress concentration on the rod which should be take into account. The developed model was also extended to a three-dimensional case study by considering the bone plate, bone screws and the cortical bone. The result obtained from the three-dimensional finite element analysis showed only about 7% error from the experimental counterpart under same conditions.