Lightweight Construction Research Articles

Investigation of mechanical and thermal properties of new type bio-composites containing camelina

Increasing urbanization has made lightweight construction materials with low thermal conductivity important. One of these materials, which has gained importance recently, is bio-composite materials consisting of agricultural wastes. The usability of camelina stalks, an agricultural waste, in the production of bio-composite has not been studied. The aim of this research is to develop new lightweight bio-composites with camelina stalks filled. For this, 11 composite mixtures using unsaturated polyester resin as the binder were created. Camelina stalks at 25, 30, 35, 40 and 45 % substitution ratios were used in half of 10 mixtures outside reference. Later, five more different mixtures by adding expanded perlite (EP) up to 5 % of the amount of camelina stalks in each mixture were produced. The physical, mechanical and thermal properties of the bio-composites produced with polyester binder were examined and the microstructure analysis was performed by SEM. The results showed that thermal conductivity, unit weight, compressive strength and ultrasonic pulse velocity (UPV) decreased as the ratio of the camelina stalks increased. The lowest thermal conductivity value was determined as 0.0842 W/(mK) in the 45 % camelina + 5 % EP filled specimen. The highest compressive strength value of the mixtures excluding the reference specimen was found to be 35.78 MPa in the 25 % camelina + 5 % EP-filled specimen. The addition of EP to the composites increased the water absorption, UPV and compressive strengths, but decreased the thermal conductivity. The results showed that camelina stalks can be used to produce sustainable bio-composites.

Design and construction of kinetic structures based on elastica strips

Ruled surfaces have been used to create kinetic designs capable of reconfiguring their shapes to adapt to the environment and enhance aesthetic qualities. However, many existing designs require complex mechanical systems and heavy construction. Simplifying the design and construction process using an elastic-kinetic approach is promising but remains underexplored. This paper proposes a new strategy to rationalize kinetic designs with curved surfaces using a series of non-intersecting elastica strips bent to the minimum energy state. Complex 3D kinetic designs can be conveniently and parametrically modeled based on simple design parameters for 2D curves. The generated shapes are systematically classified into four categories. As a proof of concept, a full-scale kinetic pavilion was designed and constructed to demonstrate the effectiveness of the proposed method in realizing lightweight, high-speed, and cost-efficient construction. An extension of the proposed method to create interactive designs using sensors and actuators is also discussed.

Investigations into Flux-Free Plasma Brazing of Aluminum in a Local XHV-Atmosphere.

As a lightweight construction material, aluminum plays a key role in weight reduction and, thus, sustainability in the transport industry. The brazing of aluminum and its alloys is impeded by the natural passivating oxide layer, which interferes with the brazing process. The presented study investigates the possibility of using a thermal silane-doped argon plasma to reduce this oxide layer in situ and thus eliminating the need to use hazardous chemical fluxes to enable high-quality brazing. Using plasma spectroscopy and an oxygen partial pressure probe, it was shown that a silane-doped argon plasma could significantly reduce the oxygen concentration around the plasma in a thermal plasma brazing process. Oxygen concentrations below 10-16 vol.-% were achieved. Additionally, metallographic analyses showed that the thickness of an artificially produced Al2O3-Layer on top of AlMg1 samples could be substantially reduced by more than 50%. With the oxide layer removed and inhibition of re-oxidation, silane-doped plasma brazing has the potential to become an economically efficient new joining method.

Experimental and statistical investigation on strength and microcracks remediation in cement mortar using expanded vermiculite as a bacterial carrier

Cement based building materials have been used in the field of construction for decades. Among the various applications, lightweight aggregates are very common for thermal insulation, improved acoustic performance, and lightweight construction. This study reported the healing of micro-cracks using expanded vermiculite as a bacterial carrier for crack healing. The expanded vermiculite was adsorbed with bacterial cells and subsequently coated using sodium silicate as the first layer and cement slurry as the second layer. The cement mortar was prepared using dual-coated expanded vermiculite as a bacterial carrier. The expanded vermiculite's water holding capacity and bacterial immobilization capacity were 180% and 1.62×109 cells/gram, respectively. The fine aggregate was replaced in the cement mortar using expanded vermiculite in 0%, 10%, 15%, 20%, and 25% to find the optimum replacement percentage for crack remediation without compromising strength and durability. The performance of this cement mortar in terms of strength, durability, and crack remediation capacity was assessed. The test results showed that 20% replacement with a 5% silica fume combination was effective. The crack area and width were determined by using ImageJ analysis. The bacteria remediated a crack width of 0.92 mm by precipitating calcite crystals was observed under FESEM and confirmed using EDS. For each test process, regression equations were formed by taking into account the variables that influence the compressive strength and healing efficacy. The variables' significance and the optimum vermiculite proportion were determined using ANOVA analysis. The factors were significant with a p-value less than 0.05, and the experimental and ANOVA general linear model predicted that 20% replacement is optimum.

Prefabricated structures of buildings from steel thin-wall cold formed profiles Cocoon "Transformer"

Cocoon System AG's light steel thin-walled structures have proven their worth in numerous superstructures, extensions, exterior wall and ceiling systems, as well as complex projects by internationally renowned architects. As part of the implementation and development of lightweight construction methods, this company has developed the Cocoon "Transformer" system, represented by prefabricated wall and floor structures with varying degrees of completeness and enlargement, registered as ETA - 11/0105. The Cocoon "Transformer" system is a frame-sheathing self-supporting or load-bearing, external or internal structure, the components of which are steel thin-walled cold-formed profiles, plate materials (cladding), insulating materials and fasteners. ETA-11/0105 suggests an optimization of this structural system. The European project ELISSA was created to improve the construction of walls, floors, roofs and volumetric modules of the Cocoon "Transformer" system with improved thermal, acoustic, vibration / seismic and fire resistance characteristics, as well as to develop industrially safe methods for their application. The use of high-performance airgel thermal insulation strips in this project minimized the effect of thermal bridging in the exterior wall structure and brought the heat transfer coefficient closer to the requirements of a passive house. The new prefabricated lightweight elements ELISSA, which demonstrate a high level of energy efficiency, provide the possibility of using insulated vacuum panels (VIP) with increased strength. The increased strength of Super Insulated VIP Panels is due to the use of foils with better endurance and also encapsulated in polyurethane. However, the version of the ELISSA system using VIP panels significantly increases the cost of the wall structure, which may hinder its widespread use in Ukraine. The creation of standard economic solutions with a sufficient level of energy efficiency according to the Cocoon "Transformer" construction concept will allow, to a certain extent, to reduce the costs of restoring the housing stock of Ukraine, damaged as a result of hostilities, and solve the problem of rapid new construction to replace completely destroyed housing.

Co-bonding of carbon fibre-reinforced epoxy and galvanised steel with laser structured interface for automotive applications

Materially bonded hybrid systems with precisely adjusted interfacial properties are of great scientific and industrial interest with regard to lightweight construction. In the present study, a material composite of carbon fiber reinforced plastic (CFRP) and galvanized steel is considered, where the metallic surface is laser structured in order to improve the adhesion properties. The resulting joining properties will be elicited by tensile shear tests in comparison to an alkaline cleaned surface condition and blind riveting. The potential of direct-joined hybrid systems with laser-structured substrate surfaces will also be considered using an automotive roof frame as an example. In the tensile shear test, the direct-joined hybrid joint with laser-structured metal substrate achieves significantly higher joint strengths than after alkaline cleaning. Compared to an aluminum/steel reference structure, the CFRP/steel roof frame exhibits a significant weight advantage with superior mechanical properties under flexural and compressive loading.

Geometric and mechanical joint characterization of conventionally and tumbled self-piercing riveting joints

In view of economic and ecological trends, the concepts for lightweight construction in transport systems are becoming increasingly important. These are frequently applied in the form of multi-material systems, which are characterized by the selective use of materials and geometries. One major challenge in the manufacturing of multi-material systems is the joining of the individual components to form a complete system. Mechanical joining processes such as semi-tubular self-piercing riveting are frequently used for this application but reach their limits concerning the number of combinations of geometry and material. In order to react to the requirements and to increase the versatility of semi-tubular self-pierce riveting, a process combination consisting of a tumbling process and a self-pierce riveting process has been presented previously. This process combination is used in this work to investigate the versatility and to identify the influencing parameters on it. For this purpose, experiments are conducted to identify process-side influence possibilities. The tests are performed with a dual-phase steel aluminum alloy to represent the varying mechanical characteristics of multi-material systems. Furthermore, the initial sheet thicknesses of the joining partners are varied in several steps. In addition to the geometric joint formation used to describe the undercut, the rivet head end position and the residual sheet thickness, the joining process, is also analyzed during the investigations. Further, the innovative joining process is evaluated by comparing it with a conventional self-piercing riveting process. The knowledge obtained represents a basis for the identification and evaluation of the versatility of the process combination.

Elastic axial stiffness properties of lattice structures: Analytical approach and experimental validation for bcc and f2cc,z unit cells

Additive manufacturing (AM) is a key technology for the individualized and resource-efficient production of structural components. Recent developments in manufacturing technologies enable improved quality of additively manufactured components and therefore they become more and more important in lightweight constructions. An example is the substitution of solid material by porous lattice structures. Those embedded lattice structures lead to highly weight-efficient structures. Most recent investigations focus on numerical and experimental studies to describe the mechanical behavior of lattice structures. In this paper, a method to determine analytical expressions for the axial stiffness properties of lattice structures is presented. The displacement method and direct stiffness method are used to derive symbolic parameter-dependent formulas for the axial stiffnesses and effective Young’s moduli for f2cc,z, and bcc unit cells. Furthermore, an empirical approach based on Finite Element simulations is presented to describe the stiffness reduction for non-embedded or rather free lattice structures. The results are further validated by physical experiments. Stereolithography is used for specimen production. f2cc,z, and bcc lattice structures are embedded in thin-walled rectangular aluminum tubes and tested under compression load. Furthermore, lattices without a surrounding tube are tested. The analytical and empirical solutions are in good agreement with the experimental and numerical results.

Loofah Sandwich Panels: The Effect of Adhesive Content on Mechanical and Physical Properties.

In the development of new materials, the focus nowadays is increasingly on their relevance with regard to lightweight construction or environmental compatibility. The idea of a lightweight sandwich panel was inspired by an increasing number of cosmetic accessories that use the fibers of the loofah plant, a rapidly renewable, light, fibrous raw material. The aim of the study was to develop a fiber composite panel based on the fibers of the loofah plant (Luffa cylindrica) as core material and wooden veneer as the skin layer to be used in areas of lead construction. Three different panel variations were produced for the tests, with a fiber–adhesive ratio between 1:1.05, 1:0.8, and 1:0.5. The mechanical strength (flexural strength and internal bond) and the physical properties (density and thickness swelling) were determined as a function of the fiber–adhesive composition. The results show that the flexural strength increased by approx. 400% and the thickness swelling was reduced by 10% with increasing adhesive quantity.

Fatigue Performance Analysis of an Existing Orthotropic Steel Deck (OSD) Bridge

Orthotropic steel deck (OSD) bridges are lightweight constructions which are convenient, especially for the achievement of long spans. Conversely, due to the stress concentration in correspondence to the numerous and unavoidable welded construction details, this bridge typology is prone to fatigue cracking under the effect of cyclic loading with high-stress amplitudes. Existing OSD bridges are particularly vulnerable to fatigue damage accumulation because of the dated standards adopted at the time of their design and the fact that heavy lorries have increased in travel frequency and weight. In the present paper, a case study of a northern Italian existing highway viaduct, built in the 1990s, is presented and analyzed. The fatigue damage accumulation was carried out according to the fatigue load models for road bridges reported in Eurocode EN 1991-2 and the assessment criteria indicated in EN 1993-1-9. The stress amplitude, in correspondence to the critical details of the bridge, is assessed by means of detailed finite-element calculations carried out with the software MIDAS GEN®. The amplitude and frequency of the travelling weights are assessed based on real traffic monitoring from the highway. Moreover, an automatic “rain-flow” algorithm is implemented, which is able to detect each nominal stress variation above the fatigue limit. In general, the bridge is not fully compliant with today’s standards when considering the entire duration of the prescribed life of the design. Countermeasures, like lane number reductions and lane reshaping, are critically analyzed since their effectiveness is questionable as far as the reduction in heavy traffic is concerned. Other interventions, like the replacement of the pavement in order to improve the stress redistribution upon the connection details below the wheel footprint, and continuous bridge inspections or monitoring, look more promising.

A Parylene-Based Ultra-Thin Printed Circuit Board As a New Platform for Flexible Sensors and Wearables

Flexible electronics and sensors are a key enabling element for the realization of wearables and geometry adaptive devices needed to follow current trends such as the Internet of things or Industry 4.0. Within this paper, we present a new and flexible packaging platform by the fabrication of an ultra-thin and highly flexible printed circuit board (PCB).The thermoplastic polymer Parylene, which combines a variety of unique properties such as optical transparency, biostability and biocompatibility according to ISO 10993, thermal stability as well as low permeability for gases and water, was used as the base for the new PCB.Particularly, its mechanical properties, especially the absence of intrinsic stresses, as well as its low Young’s modulus and good bendability are advantageous when using Parylene films as a free-standing substrate for flexible applications. The chemical inertness of Parylene against all common acids, bases and solvents ensures its compatibility with established standard microsystem technologies.For the realization of ultra-thin flexible PCBs, Parylene was used as a substrate as well as for the encapsulation and protection layer, respectively. Furthermore, Parylene was the dielectric between the metallic conductive layers. These redistribution layers (RDL) were deposited and patterned by standard microsystem technologies, such as sputtering, lithography and wet chemical etching. Hence, structure sizes of down to 10 µm were successfully realized. Different metals, such as gold, copper, and aluminum were tested for the RDL. Alternatively, printing technologies such as screen printing and aerosol jet printing were successfully demonstrated for the if conductive silver layerse. The electrical connection between the various RDL was of special interest throughout the study and was realized by etching vertical vias through the Parylene using oxygen plasma. Due to the low total thickness of the flexible Parylene PCB of 20 µm or even less, the obtained vias through the Parylene feature an advantageous low aspect ratio. For the contact formation through the vias, different methods were investigated, e. g. sputtering, printing and electrochemical deposition.Finally, the fabricated flexible Parylene PCB were characterized with respect to their bendability and electrical properties. Doing so, the resistivity and capacitance were measured as well as the frequency response between 20 kHz and 500 MHz. Particularly, for frequencies below 1 MHz the realized flexible Parylene PCBs show a good electrical performance.A third function of Parylene with respect to the realization of an ultra-thin and flexible PCB is its usage as a barrier or capping layer. Doing so, new approaches such as embedding electronic or sensor components in the flexible PCB can be enabled. Other integration technologies such as wire bonding, printing or gluing were investigated with respect to their usability for the new flexible PCB as well. Besides, also the direct fabrication of sensors on the Parylene flexible PCB was successfully demonstrated by the realization of a flexible potentiometric pH sensor.The presented new type of ultra-thin PCB is a versatile platform for the realization of flexible electronics, sensors and devices. Due to its biocompatible properties, the flexible Parylene PCB can be used for medical applications but also for the integration of MEMS, chemical sensors and optical components, respectively. Doing so, it enables the realization of smart systems for wearable applications and their integration into light weight constructions. Within this paper, the concept of this new approach, the respected fabrication and integration technologies as well as possible applications are presented in detail. Figure 1

Development and characterization of an automated portable wound irrigation device for diabetic ulcers

<p>Patients with diabetes mellitus may experience peripheral neuropathy and extremity system impairment, which may lead to ulceration if the treatments are delayed. Diabetic ulcers, unfortunately, are chronic, which require proper treatments, including debridement and bacterial removal using an irrigation device. To date, commercial irrigation devices included pulsed-lavage, bulb syringe, and gravity bags. Unfortunately, the devices have limitations in terms of portability, measurability, controllability, and disposability. To tackle the limitations, this study aims to design, fabricate, and characterize an automated portable wound irrigation device (Apdice), which is controllable non-disposable, and portable. The device was designed and fabricated using a lightweight construction, a rechargeable battery, and non-disposable materials to support the portability and non-disposable means. Meanwhile, the proportional-derivative-integral controller with its peripheral components were featured to enable controllability. Furthermore, the device was also tested regarding the contamination using a particle counter, and appeared to be contamination free. In short, Apdice showed a robust technological performance. However, it is also worth the try to test the contamination test against biological agents to guarantee the biocompatibility of the device.</p>

Hydrothermal synthesis of an expanded perlite based lightweight composite for indoor humidity regulating

• A lightweight tough composite could be synthesized from EP for humidity regulating. • Tobermorite formation could enhance strength and improve porosity of the material. • CaCl 2 addition could promote porosity and improve moisture adsorption/desorption. • CMC formation could form crosslinked networks thus improving humidity regulation. • Both CaCl 2 and CMC addition had large effect on regulating humidity synergetically. A lightweight and tough indoor construction material has been synthesized hydrothermally from expanded perlite (EP) with indoor humidity regulation for high-rise buildings. Due to the low-temperature (≤473.15 K) hydrothermal treatment, the original porosity of EP was remained in the matrix to serve a low density (<0.900 g/cm 3 ). The formation of C S H and tobermorite could not only enhance the flexural strength of the composite (greater than 16.0 MPa), but also improve its porosity. The CaCl 2 addition had a capability of promoting the porosity and improving the moisture adsorption/desorption capacity. The CaCl 2 solution could make more moisture adsorbed in pores and more pores possess the humidity self-regulation ability. The CMC addition could generate crosslinked networks and high osmotic pressure to promote humidity self-regulating performance greatly. Furthermore, the addition of both CaCl 2 and CMC exerted a synergetic effect to further reinforce moisture adsorption capacity (∼380 g/m 2 ).

The mechanisms of the high-strain-rate superplastic deformation of Al-Mg-based alloy

High-performance aluminum-based alloys exhibiting a high-strain-rate superplasticity improve the formability of lightweight constructions with complex shapes. The microstructural evolution and contributions of the deformation mechanisms to the total strain during high-strain-rate superplastic deformation of Al-Mg-based alloy with minor Sc and Zr additions were analyzed. Strain-induced changes in the grain/subgrain structure confirmed the dynamic recrystallization even at large strains. The evolution of the surface structure with focus ion beam milled grids confirmed that grain boundary sliding provided up to 40% of the total strain. The role of dislocation slip/creep increased and diffusional creep decreased with an increase in the strain rate.

Modeling and Simulation of Mechanical Performance in Textile Structural Concrete Composites Reinforced with Basalt Fibers

This investigation deals with the prediction of mechanical behavior in basalt-fiber-reinforced concrete using the finite element method (FEM). The use of fibers as reinforcement in concrete is a relatively new concept which results in several advantages over steel-reinforced concrete with respect to mechanical performance. Glass and polypropylene (PP) fibers have been extensively used for reinforcing concrete for decades, but basalt fibers have gained popularity in recent years due to their superior mechanical properties and compatibility with concrete. In this study, the mechanical properties of basalt-fiber-reinforced concrete are predicted using FEM analysis, and the model results are validated by conducting experiments. The effect of fiber-volume fraction on the selected mechanical performance of concrete is evaluated in detail. Significant improvement is observed when the loading is increased. There are superior mechanical properties, e.g., load bearing and strain energy in basalt-fiber-reinforced concrete as compared to conventional concrete slabs reinforced with gravel or stones. The results of the simulations are correlated with experimental samples and show a very high similarity. Basalt-fiber-reinforced concrete (BFRC) offers a lightweight construction material as compared to steel-fiber-reinforced concrete (SFRC). Further, the problem of corrosion is overcome by using this novel fiber material in concrete composites.

Design and development of self-aligning troughing idler used in belt conveyor system

Self-aligning idler provides a unique solution for rectifying the belt mistracking and aligning the belt to its centerline. A misaligned conveyor will cause the belt to run off-center to one side. In this study, the existing self-aligning idler assembly being used for belt conveyors has been analyzed and an alternate assembly is designed to overcome limitations in the existing system.The newly designed assembly takes an edge over the existing assembly as it gives flexibility for adjusting the troughing angle and varying design capacity. The taper rollers are used instead of flat idler rollers which are self-actuating and provide a quick response system. The idler bracket is also modified to optimize the weight and cost of the total idler assembly. For the first time, the newly developed assembly offers the advantage of variable conveyor capacity and Troughing angle adjustment. Also, the assembly assures the lightweight construction to optimize conveyor power requirements.

Designing bended pipes under internal pressure

There are major benefits, e.g. in the aerospace sector, for lightweight mobile applications, because of integral lightweight design and construction. Integral lightweight design avoids parting points, as they increase the weight and at the same time could cause defects. Pipe technology is a potential application for this issue. For the design of bended pipes, there are various conventional but only few FEM-based approximation methods that consider fiber plastic composites. This optimization was carried out, especially for high-pressure components with an expected burst pressure of approx. 1,050 bar (approx. 15,200 psi), consisting of liner and multi-layer laminate. Three different optimization methods with adapted material parameters were compared. The net theory was used first. Furthermore, the Tsai–Wu failure criterion was considered. The inter-fiber-failure-criterion of Cuntze has been used for straight pipes. Subsequently, variations in terms of curvature angles, curvature radii, and pipe size for various laminates has been shown in theoretical investigations. The result section provides the inverse reserve factor and an outlook on the expected weight for various fiber combinations.

Numerical optimization of supercharging and combustion on a two-stroke compression ignition aircraft engine

Two-Stroke (2S) Compression Ignition (CI) engines have been used in aviation since World War II, for their excellent fuel efficiency and lightweight construction. In a modern light aircraft, these advantages still remain, along with the capability to run on jet fuel instead of gasoline. However, the design of these engines must be deeply revised, in order to incorporate the recent technologies, and it must be optimized with the support of CAE tools. The paper presents a CFD optimization of a turbocharged 2S CI 5.6 L flat-six aircraft engine developed by CMD. The scavenging system is of the Uniflow type, with exhaust poppet valves and a set of piston-controlled ports along the cylinder liner. Two mechanical superchargers are serially connected to the turbochargers. The crankshaft can be directly coupled to the propeller, thanks to its excellent balance and the relatively low maximum engine speed (2600 rpm). Differently from previous papers published on the same engine, the current study is focused on two crucial design topics: the optimization of the supercharging system and of the injection strategy. A customized version of KIVA-3V is used for the 3D-CFD cylinder analyses, while a commercial 1D-CFD code is employed to model the whole engine. The study is supported by a comprehensive experimental campaign, that permitted the accurate calibration of the numerical models. In comparison to any Four-Stroke delivering the same maximum power (400 HP at 2600 rpm, sea level), the analyzed engine is very light (about 220 kg), and efficient (211 g/kWh at typical cruise conditions). Despite the high performance, peak cylinder pressure and turbine inlet temperature at sea level are relatively low: 125 bar, 850 K. At rated power (360 HP@2400 rpm, sea level) combustion is complete and smoke-less, thanks to the optimization of the injection strategy, supported by the previous CFD analysis. The engine can operate at altitudes as high as 5500 m (18,000 feet), still delivering 270 HP at 2400 rpm, without relevant reduction of fuel efficiency. The key for the performance at high altitudes is the choice of the turbocharger considering the compressor choke limit easly reachable at high altitudes.

RoofKIT - Circular Construction and Solar Energy Use in Practice at the Solar Decathlon Europe 21/22

The contribution of the RoofKIT team to the SDE 21/22 competition is the extension for an existing café in Wuppertal, Germany, to create new functions and living space for the building with simultaneous energetic upgrading. The energy concept targets all renewable resources available on and in the building for energy supply: mainly solar energy which is used via PVT collectors, as well as waste heat from ventilation and grey water which is recovered for pre-heating. As part of the competition, a demonstration unit will be built representing a small cut-out of the extension. An integral building and energy concept combines physical properties of the building with adapted building services technologies to achieve maximum indoor comfort – particularly considering possible overheating of the lightweight construction during summer – and minimum CO2 emissions. The latter extends to the whole lifecycle of the building unit and one of the major goals of the project is to realize an almost completely mono-fraction and circular building construction as a contribution to the urban mining concept.

The potential of lightweight panel systems in building industry

The current construction technologies are often characterized as ineffective, with long construction times, heavy structural weight, increased financial and labour cost, and environmentally unsustainable. Innovative construction methods, including modern lightweight panel systems, are characterized by low weight (this affects not only transport characteristics but also the production, such as easier handling of the panels), faster construction time, the guaranteed quality due to industrial production in a factory, economic efficiency and many other benefits. The presented study examined the potential of efficiency and performance of four variants of lightweight construction panels in the context of the required essential properties of prefabricated construction elements, as well as in comparison with the variant of "heavy" prefabricated concrete panel system.