Lightweight Construction Research Articles

Probing the effect of post-curing and halloysite nanotube reinforcement on thermo-mechanical properties of lightweight epoxy syntactic foam composites

This paper deals with an investigation of the post-curing effect of halloysite nanotubes (HNTs) reinforced syntactic foam (HRSF) containing cenosphere as hollow inclusion at 0, 20, and 40 vol% in an epoxy matrix. Compression, flexural, and thermal properties of HRSF (1 vol% HNTs) and cenosphere/epoxy syntactic foam (CESF) composites without HNTs are studied under the influence of post-curing. Further, the post-cured HRSF containing 40 vol% cenosphere (NSF40_H) exhibited a compressive modulus of 33.2% higher than room temperature cured neat epoxy due to improved crosslinking. Addition of HNTs in NSF40_H augments the flexural modulus up to 26.9% compared to post-cured neat epoxy. Additionally, the glass transition temperature ( Tg) of CESF composites with 40 vol% cenosphere was increased by 24.3 °C compared to the room temperature cured sample. This positive shift in Tg can be attributed to the beneficial impact of post-curing, as indicated by differential scanning calorimetry study. Thermogravimetric results demonstrated better thermal stability of HRSF relative to CESF and neat epoxy composites. Transmission electron microscopy illustrated the structure-property correlations of nanotube reinforcement. The improved properties of syntactic foams could be viewed as a potential material for lightweight constructions, especially in the marine and automobile industries.

Development and evaluation of green fired clay bricks using industrial and agricultural wastes

Green construction materials have emerged as viable options to cope with the sustainability challenges set by the global communities without compromising the technical merits. Agro-industrial wastes have been utilized as alternative components in manufacturing construction products. In this vein, burnt clay bricks (CBs) is one of the novel and viable waste disposal strategy. Therefore, the primary focus of this research is to examine the impacts of agro-industrial wastes, such as sludge waste (SW), steel slag (SS), wood ash (WA), and banana ash (BA) on various physical, mechanical, and microstructure characteristics. The green CBs were prepared by admixing the wastes at a 5%, 10%, 15%, and 20% dosage. The binary blended CBs were dried under the sun for 7 days before being fired at 900 °C for 3 hrs. The CBs containing SW, WA, and BA exhibited lower compressive strengths of ∼67% than the control and SS blended specimens depending on the chemical composition and particle size distribution of the source material. The microstructural analysis of the CBs incorporating the wastes tented to improve with the addition of waste precursors and governed by the Ca/Si ratio. The outcomes revealed the potential of attaining reduced bulk density for the light-weight and cost-effective constructions with low volume (5%) replacement of studied wastes in the clay mixture. The scanning electron microscopic (SEM) analysis revealed a relatively compact matrix of the control and SS-based specimens which tended to improve the engineering properties of developed CBs.

Enhancement and Function of the Piezoelectric Effect in Polymer Nanofibers.

ConspectusThe realization of intelligent, self-powered components and devices exploiting the piezoelectric effect at large scale might greatly contribute to improve our efficiency in using resources, albeit a profound redesign of the materials and architectures used in current electronic systems would be necessary. Piezoelectricity is a property of certain materials to generate an electrical bias in response to a mechanical deformation. This effect enables energy to be harvested from strain and vibration modes, and to sustain the power of actuators, transducers, and sensors in integrated networks, such as those necessary for the Internet of Thing. Polymers, combining structural flexibility with lightweight construction and ease of processing, have been largely used in this framework. In particular, the poly(vinylidene fluoride) [PVDF, (CH2CF2)n] and its copolymers exhibit strong piezoelectric response, are biocompatibile, can endure large strains and can be easily shaped in the form of nanomaterials. Confined geometries, improving crystal orientation and enhancing piezoelectricity enable the fabrication of piezoelectric nanogenerators, which satisfy many important technological requirements, such as conformability, cheap fabrication, self-powering, and operation with low-frequency mechanical inputs (Hz scale). This account reports on piezoelectric polymer nanofibers made by electrospinning. This technique enables the formation of high-aspect-ratio filaments, such as nanowires and nanofibers, through the application of high electric fields (i.e., on the order of hundreds of kV/m) and stretching forces to a polymeric solution. The solution might be charged with functional, organic or inorganic, fillers or dopants. The solution is then fed at a controlled flow rate through a metallic spinneret or forms a bath volume, from which nanofibers are delivered. Fibers are then collected onto metallic surfaces, and upon a change of the collecting geometry, they can form nonwovens, controlled arrays, or isolated features. Nanofibers show unique features, which include their versatility in terms of achievable chemical composition and chemico-physical properties. In addition, electrospinning can be up-scaled for industrial production. Insight into the energy generation mechanism and how the interaction among fibers can be used to enhance the piezoelectric performance are given in this paper, followed by an overview of fiber networks as the active layer in different device geometries for sensing, monitoring, and signal recognition. The use of biodegradable polymers, both natural and synthetic, as critically important building blocks of the roadmap for next-generation piezoelectric devices, is also discussed, with some representative examples. In particular, biodegradable materials have been utilized for applications related to life science, such as the realization of active scaffolds and of electronic devices to be placed in intimate contact with living tissues and organs. Overall, these materials show many relevant properties that can be of very high importance for building next-generation, sustainable energy harvesting, self-rechargeable devices and electronic components, for use in several different fields.

Structural principles of an asymptotic lamella curtain wall

Asymptotic lamella structures are a new lightweight construction system that allows fabrication from straight and flat strips of material that are elastically formed into a doubly curved design geometry. To study the structural potential of asymptotic building facades withstanding wind loads, a full-scale curtain wall prototype was constructed and analysed. Deflection tests with vertical loading and lateral point loading show that the structure is most likely to fail due to the lateral-rotational buckling and compression buckling. An inductive regression method is presented that combines analytical solutions with the finite element simulation to study the structural principles. In this way, the deflection of the structure can be quantitatively divided into bending, torsion and shear deformation under a specific loading condition. Under wind loads, the bending and the torsion deformation take a major part in the resultant deflection, and the structure can be regarded as a curved beam grillage. Finally, several design strategies, including numeric optimization of the profile dimensions, are proposed to improve the structure for future applications.

Correlation between sound insulation and occupants’ perception – Proposal of alternative single number rating of impact sound, Part III

Through a series of Swedish research projects carried out over twelve years, the relation between the measured impact sound insulation and the corresponding subjective rating given by residents of multi-storey apartment buildings has been studied. Previous results, based on a limited number of building cases, suggested the need to include frequencies below 50 Hz in a frequency weighted single number quantity to get a reasonable correlation with the subjective ratings.The purpose of this paper is to include an extended amount of data compared to the previous studies to secure more substantiated results. Data has been examined for 38 building cases, including a variety of lightweight and heavy constructions. More than 1200 questionnaire responses form the basis for comprehensive statistical analyses.The results confirm the conclusions of the previous parts (I, II), stating that frequencies below 50 Hz are of importance when evaluating impact sound insulation, primarily in lightweight buildings. The correlation between measured weighted single number quantities and annoyance ratings increases significantly when the frequency range is extended down to 25 Hz. The strongest correlation was obtained when evaluating the impact sound insulation, again from 25 Hz, when using the weighted single number quantity LnT,w + CI,25–2500 where the CI-term is evaluated according to ISO 717-2 amended to the extended frequency range 25–2500 Hz. It is also suggested that in the lowest one-third octave bands, 25–40 Hz, there is no need to normalize the impact sound pressure levels with respect to the reverberation time.

Simulation and Optimization of Rectangular Microstrip Patch Antenna for Mobile 5G Communications

Microstrip or patch antennas are becoming increasingly useful because they can be printed directly onto a circuit board. The microstrip antennas are becoming very widespread within the mobile phone market. Patch antennas are low fabrication cost, have lightweight, and are easily fabricated. The lightweight construction and the suitability for integration with microwave integrated circuits are two more of their numerous advantages. This work introduces a design of a rectangular Microstrip Patch Antenna (MPA) at a frequency of 28 GHz using the finite integration technique of the Computer Simulation Technology (CST). The simulated antenna is employed for the 5G mobile communication. The inset-fed technique has been used to feed the rectangular MPA because it is easy to fabricate and provides simplicity in modelling as well as impedance matching. In order, to facilitate the fabrication and reach the best results, an attempt has been made to improve parameters through optimized patch dimensions by trial and error. A reasonable gain, bandwidth, radiation pattern, and return loss have been obtained after the antenna simulation process was completed.

Fine Blanking Limits of Manganese-Boron-Steel in Fine Blanking Compared to Tempered Steel with Variation of Sheet Metal Temperature

Fine blanking is a key technology for the near-net-shape production of sheet metal components. It is often used in combination with processes such as deep drawing. With increasing environmental requirements, the processing of materials with lightweight construction potential is becoming more and more important. A group of materials with high potential for lightweight construction, not only due to their suitability for hot stamping, is the group of manganese-boron steels. The fine blanking properties of these steels have not yet been exhaustively investigated. In this work, the fine blanking properties of the manganese-boron steel 40MnB4 were investigated in comparison to the quenched and tempered steel 42CrMo4. This was done using a star-piece fine blanking layout with investigation of die roll as well as tooth tip cracking. Furthermore, an investigation of the high-temperature fine blanking properties were investigated by means of inductive heating prior to fine blanking. The process forces were evaluated depending on the sheet metal temperature. A good fine blanking capability of 40MnB4 could be confirmed. Process forces and product quality were comparable to 42CrMo4 steel. Accordingly, an industrial application of fine blanking to manganese-boron steels seems highly promising.

Identification of Influencing Factors in Machine Hammer Peening with Consideration of Lubricant Influences

Lightweight construction and performance requirements in the automotive industry have resulted in increased power density. At the same time, this increases the load on the workpieces. To counteract the resulting wear, either a more wear-resistant material may be applied or the functional surface may be specifically modified against wear. Machine hammer peening (MHP) is a process for such a targeted adjustment of the functional surface and the surface area properties. MHP is a mechanical surface treatment, which increases the wear resistance of the workpieces by introducing residual compressive stresses and work hardening as well as by smoothing or structuring the surface. To ensure an accurate adjustment of the surface properties, the influencing factors (material, process parameters and lubricant) and their interactions must be sufficiently well studied and understood. In particular, the influence of the lubricant on the surface area properties has not yet been adequately investigated. The objective of the work presented in this paper was to provide a deeper insight into the influence of the type of lubricant on the resulting surface properties in terms of roughness, residual stresses and hardness. The lubricant’s influence was investigated using a partial factorial experimental design. Additional factors investigated, besides the choice of lubricant, were stroke, distance of indentation and step over distance. The results show a strong influence of the lubricant selection, especially on the resulting surface roughness. For the same process parameters, a deviation of 540 % in the resulting surface roughness was measured between two surfaces machined with different lubricants.

A Novel Method for the Determination of High Temperature FLCs of ECAP-Processed Aluminum AA5083 Sheet Metal

In this study, investigations into the deformation behavior of aluminum AA5083 at elevated temperatures were carried out on a newly developed test rig. The test rig was developed jointly with ZwickRoell GmbH & Co. KG (Germany) and is based on a Nakajima test carried out with heated dies. In this way, statements can be made about the lightweight potential of the alloy. Additionally, equal-channel angular pressing (ECAP) was performed to process the aluminum sheet metal. The conventional ECAP process is mainly used for bulk material in laboratory use and therefore is often not suitable for many industrial applications, especially for large series. The use of sheet metal allows a significant increase in the areas of application. It is documented in conventional ECAP that grain refinement is achieved by the severe plastic deformation. At room temperature this primarily increases the mechanical strength. Formability is improved in fine-grained materials, especially at elevated temperatures, which is related to diffusion-controlled deformation mechanisms and grain boundary sliding. The advantages of ECAP for sheet materials are thus also in lightweight construction and can even optimize the use of the AA5083 alloy. ECAP-route C was used for the process to provide the most homogeneous microstructure possible (180° rotation around the ECAP-axis after the first pass). Nakajima specimens were taken from the processed sheet materials to determine the Forming Limit Curve (FLC) compared to the reference material (four different specimen geometries). FLCs under elevated temperatures (250 °C, 375 °C) were performed on the novel Nakajima test bench. A special feature of the test rig is the rapid heating to avoid microstructural changes. Microscopic examinations were performed after the deformation to study the deformation mechanisms. Differences of the forming and fracture mechanisms between the reference alloy and the ECAP material were found.

Influence of Macro-Structured Tools on the Formability of Aluminum Alloys in the Cryogenic Temperature Range

Aluminum materials are popular materials for research in terms of lightweight construction. How cryogenic forming can be used to increase material utilization in terms of resource efficiency is one of the areas being investigated. Subject of this study are numerical and experimental investigations regarding the formability of the aluminum alloy AA6014-T4 with macro-structured deep drawing tools at cryogenic temperatures. The macro-structure of the deep drawing dies significantly reduces the heat flux between the dies and the blank due to the reduced contact area. For this reason, active cooling or heating of the dies is not required. The process of heat conduction between the tool and the blank, as well as the deep drawing process, is calculated using the FE-method and compared with the experimental investigations. In addition, the induced residual stresses are determined using the hole-drilling method and compared with the computational solution. The presented examination shows an improved deep drawing ratio of the aluminum alloy AA6014-T4 at cryogenic blank temperature without active tool cooling. Additionally, the influence of the blank temperature on the forming regarding the residual stresses in the cups is analyzed and discussed.

Numerical and Experimental Investigations on the Mechanical Properties of Milled Specimens from an AA7020 Tube

The reduction of weight is crucial in the automotive sector to reach a lower energy consumption and an increased range, especially for electrically powered vehicles. In this regard, body-in-white parts offer a high potential for the application of lightweight construction. The required weight savings can be achieved by implementing parts with a high strength-to-weight ratio. A promising approach is the combination of lightweight materials and lightweight design, which can be realized by tubular components made of high strength aluminum. Due to their structural stiffness and high crashworthiness, those structures are often used as safety-relevant car body components. However, the material characterization of tube profiles is a major challenge, which in turn impedes an accurate numerical simulation and precise process design. In contrast to flat semi-finished parts, various effects of the production process and the geometry, regarding the stress state under load, must be taken into account. For this purpose, adapted testing methods considering the geometrical and mechanical properties of the tubular parts have to be investigated, in order to generate an accurate material model and process design. Within this research work, tubular components made out of AA7020 in W-temper condition were used to analyze the mechanical properties. In this regard, several tensile specimens are milled from a tube, so they also have a curvature profile. The experimental tensile tests have been performed at different strain rates by using an universal testing machine from type Gleeble 3500. To ensure a proper measurement of the mechanical properties, the clamping jaws of the testing machine are adjusted to the curved samples. The investigated material parameters are subsequently transferred to an FE-Model with curved specimen to enable an accurate prediction of the forming behavior. In addition, an FE model of a flat tensile specimen was also created for comparison, in order to gain a profound knowledge regarding the influence of the geometric and mechanical properties of tubular components.

Evaluation of Cold Roll Forming Strategies for the Production of a High-Strength Aluminum Hat Profile

High-strength aluminum alloys, such as the AA7075 alloy, offer great potential for lightweight construction thanks to their high specific strength. However, high strength and low ductility are a challenge for processing these materials. In our study, three different process routes (T6, W-Temper, O) for roll forming of a hat profile are investigated experimentally and in an FE-simulation. Since the targeted production of the hat profile is hindered due to material failure in T6-condition, inline induction heating and subsequent water spray quenching is used to bring the material to the W-Temper state before roll forming. As a third option, a pre heat treatment is applied to a soft annealed (O) material state. The experimental results show fundamental differences of the forming processes, depending on the tempering condition. The FE-simulation involves the roll forming process for the production of a hat profile and shows a high agreement with the experiments. Finally, the experimental results demonstrate how inline solution annealing by induction heating for the W-Temper process affects the properties and the quality of the profiles produced.

Further Development of an Adaptive Joining Technique Based on Friction Spinning to Produce Pre-Hole-Free Joints

Mechanical joining processes are an essential part of modern lightweight construction. They permit materials of different types to be joined in a way that is suitable for the loads involved. These processes reach their limits, however, as soon as the boundary conditions change. In most cases, these elements are specially adapted to the joining point and cannot be used universally. Changes require cost-intensive adaptation of both the element and the process control, thus making production more complex. This results in high costs due to the increased number of auxiliary joining element variants required and reduces the economic efficiency of mechanical joining. One approach to overcoming this issue is the use of adaptive auxiliary joining elements formed by friction spinning. This article presents the current state of research on pre-hole-free joining with adaptive joining elements. The overall process chain is illustrated, explained and analyzed. Special attention is paid to demonstrating the feasibility of pre-hole-free joining with adaptive joining elements. The chosen mechanical parameters are subsequently listed. Finally, a comprehensive outlook of the future development potential is derived.

Corrosion Phenomena and Fatigue Behavior of Clinched Joints: Numerical and Experimental Investigations

Lightweight construction has increasingly become the focus of scientific research in recent years, not least due to the constantly increasing fuel price, which is a key factor in the economic viability of many companies. In this respect, the use of hybrid structures, made of dissimilar materials offers many advantages. However, such hybrid structures often have undesirable side effects. For example, brittle intermetallic phases are formed when aluminum and steel are welded. Clinching as a mechanical joining process does not produce such intermetallic phases since the connection is realized through form and force closure. In this process, a punch passes through two or more sheets and forms them into a permanent joint in a die. In the present work, the corrosion phenomena of an aluminum-steel clinched joint have been investigated by both experiments and numerical simulations in order to explain the superior fatigue behavior of pre-corroded joints. Therefore, the clinched joints have been corroded by a three-week salt-spray test. In addition, the electric potential and the von Mises stress are calculated under the assumption of a static loading. The results of both experiments and numerical simulations can explain the improvement in the fatigue behavior of the corroded specimens. This phenomenon can be attributed to the accumulation of corrosion products in small gaps between the joined metal sheets.

Biological Concepts as a Source of Inspiration for Efficiency, Consistency, and Sufficiency

Sustainable development is a global challenge addressed by the 2030 Agenda with internationally adopted goals. The consideration of the three major sustainability strategies of efficiency, consistency, and sufficiency can guide us toward more sustainable policy approaches, product manufacturing, service offers, and consumption lifestyles. We select the growth form “liana”, which has evolved several times independently, to identify traits of lianas and general biological concepts derived therefrom. Even though sustainability is an anthropocentric approach and does not exist in biology, we can attribute biological concepts to sustainability strategies. The biological concepts of lightweight construction, modularity, function-related tissue formation, and trade-off can be attributed to efficiency; the concepts of zero waste, best fit, and damage repair to consistency; and the change of growth form and the concept of less is more and good enough to sufficiency. We discuss the analogies between parasitic architecture and the “structural parasitism” of lianas on host trees and between polymers with switchable autonomous properties and ontogenetic changes in the lianescent growth form. Efficiency can be analyzed quantitatively and consistency qualitatively, whereas sufficiency, as an aspect of human consumption patterns, cannot be mathematically measured. Biological concepts can thus serve as a source of inspiration for improving sustainability in the technosphere.

MEMS Vibrometer for Structural Health Monitoring Using Guided Ultrasonic Waves

Structural health monitoring of lightweight constructions made of composite materials can be performed using guided ultrasonic waves. If modern fiber metal laminates are used, this requires integrated sensors that can record the inner displacement oscillations caused by the propagating guided ultrasonic waves. Therefore, we developed a robust MEMS vibrometer that can be integrated while maintaining the structural and functional compliance of the laminate. This vibrometer is directly sensitive to the high-frequency displacements from structure-borne ultrasound when excited in a frequency range between its first and second eigenfrequency. The vibrometer is mostly realized by processes earlier developed for a pressure sensor but with additional femtosecond laser ablation and encapsulation. The piezoresistive transducer, made from silicon, is encapsulated between top and bottom glass lids. The eigenfrequencies are experimentally determined using an optical micro vibrometer setup. The MEMS vibrometer functionality and usability for structural health monitoring are demonstrated on a customized test rig by recording application-relevant guided ultrasonic wave packages with a central frequency of 100 kHz at a distance of 0.2 m from the exciting ultrasound transducer.

More Constructions of Light MDS Transforms Based on Known MDS Circulant Matrices

Maximum distance separable (MDS) codes have the maximum branch number in cryptography, and they are generally used in diffusion layers of symmetric ciphers. The diffusion layer of the Advanced Encryption Standard (AES) uses the circulant MDS matrix with the row element of {2;3;1;1} in F28. It is the simplest MDS matrix in F2n4, recorded as A=Circ(2;3;1;1). In this paper, we study the more extensive MDS constructions of A in F2n4. By transforming the element multiplication operation in the finite field into the bit-level operation, we propose a multivariable operation definition based on simple operations, such as cyclic shift, shift, and XOR. We apply this multivariable operation to more lightweight MDS constructions of A and discuss the classification of the MDS clusters. We also give an example of the MDS cluster of A. Without changing the structure, elements, and the implementation cost of the known MDS matrix, the number of existing MDS transformations is expanded to n2/2 times that of its original. The constructions in this paper provide rich component materials for the design of lightweight cryptographic algorithms.

Performance of Expanded Polystyrene (EPS) sandwiched concrete panels subjected to accelerated corrosion

Expanded Polystyrene (EPS) Sandwiched Concrete Panel is economical and light weight construction material which functions as load bearing as well as insulating member. EPS sandwiched concrete panels are advantageous in rapid construction of houses as well as saving of materials. This experimental study attempts to assess the out-of-plane behavior (four-point flexural bending) and performance of EPS sandwiched concrete panels subjected to varying degrees of corrosion using impressed current corrosion technique. EPS panels with dimensions of 1000 × 600 × 130 mm (Length × Width × Thickness) with welded wire mesh of size 50 × 50 mm as wythe reinforcement were corroded to different levels and tested under a monotonically increasing load. The mode of failure and behavior of corrosion damaged EPS sandwiched concrete panels has been investigated in terms of resultant strength, stiffness, ductility and composite action. The experimental study shows a decrease of 6.98%, 13.93%, 20.62%, and 60.45% in the ultimate flexural load carrying capacity after exposure to 5, 10, 15, and 20 days of accelerated corrosion, respectively. The ductility of panels evaluated using Ductility Factor (DF) shows a decrease up to 85.01 % in highly corroded EPS panel. Along with destructive flexural testing, non-destructive technique of Acoustic Emission (AE) monitoring was also attempted during flexural testing using surface mounted AE sensors to correlate to the performance of corroded EPS panels. AE parameters of cumulative AE hits and their amplitudes could easily relate to the extent of damage experienced with increasing levels of corrosion.

BUILDING CLIMATIC PROPERTIES OF LIGHTWEIGHT FACADES

Lightweight constructions are assumed to not have the same performance as massive constructions regarding building physics and climate. Experimental studies show however that lightweight building envelopes made of textile-reinforced concrete are hygrothermal at least equal to conventional envelopes. Thus, it was proven that lightweight constructions have good properties concerning indoor and surface climate as well as durability. In addition, textile-reinforced concrete contributes to sustainable building, such as reducing the needed amount of cement and sand. In this study, a facade of textile-reinforced concrete was developed that surpasses or at least is equal to most building physical properties of conventional constructions. Furthermore, selected requirements for building physics and architecture (e.g., thermal energy storage over the day) were examined and compared to conventional constructions. The main results are: It has been found that lightweight constructions made of textile concrete exceed the contribution to summer thermal protection in most cases compared to conventional building constructions. These results will form the basis for future ways of building facades. They will be much lighter and thus architecturally more appealing without adversely affecting the buildings’ physical and climatic properties.

AMARETO – Saxon Alliance for MAterial‐ and Resource‐Efficient TechnOlogies

AMARETO – Saxon Alliance for MAterial‐ and Resource‐Efficient TechnOlogies