Lightweight construction

Lightweight panel with paper honeycomb

Lightweight construction is a construction philosophy that aims both to save weight and to increase resource efficiency. The motivation for lightweight construction can vary in nature.

The aim of lightweight construction is to save raw materials, costs and energy in the manufacture, use and recycling of a product. Especially with moving masses (road and rail vehicles, elevators, robot arms, machine components, etc.), lightweight construction can reduce operating costs or increase the payload. In the case of vehicles and aircraft, for example, a lower drive power is required for the same driving or flight characteristics, while fuel consumption is reduced and the ratio of vehicle to freight weight is improved. In this way, the overall device, drive source and fuel supply can be made smaller (spiral weight). The savings in the operation of the optimized product are often offset by additional expenditure in development, manufacture and assembly (optimization problem).

Today, lightweight construction is important in all industries, including vehicle construction , shipbuilding and aircraft construction . Lightweight construction is particularly important in space travel . Here, every kilogram of payload causes 30 to 100 kg of additional weight for rocket and fuel, so that great savings can be achieved through lightweight construction. Lightweight construction is also valued as an inexpensive and flexible alternative in building construction , especially in the construction of production , assembly and storage halls .

Metallic lightweight materials are z. B. aluminum , magnesium , high-strength steels and titanium . In addition, apply fiber composites as a classic lightweight materials. The demand for lightweight materials increased by 300% between 2002 and 2007.

Examples

Concept for lightweight aircraft seats with a mass of 3.8 kg per seat

• Many manufacturers use aluminum engine blocks in vehicle construction. Although these are lighter than conventional cast iron engine blocks , the material is less rigid and more expensive. Weight reduction increases driving performance (motorsport) with the same performance.
• In 1948, the Land Rover was the first production vehicle with large body parts made of aluminum sheets, although not for reasons of lightweight construction.
• In aircraft construction, aluminum parts were used even before vehicle construction.
• The Citroën DS (1955) was the first to have a large freeform part (the bonnet) made of aluminum and a plastic roof.
• Of Matra made Matra 530 , Bagheera Murena and Renault Espace were similar to the satellite , provided with a supporting skeleton made of tubular steel sections, which was covered with lightweight panels made of fiber-reinforced plastic. The vehicle mass of the 4.25 m long Espace of the first model generation from 1984 was 1200 kg at the level of a mid-range car.
• The Jaguar XE (model year 2015) has the highest proportion of aluminum in the mid-range segment with 75 percent. Based on a modular lightweight platform, it achieves a body-in-white weight of only 251 kilograms thanks to the high-strength alloy RC5754, which is made almost entirely of recycled aluminum .
• The Eiffel Tower is considered to be a lightweight construction inspired by nature; The model was the beam structure of the bones .

Lightweight construction principles

There are different principles for designing a lightweight solution. The design phase of the product, the actual construction phase and the production phase are ideal for implementation. Often the lightweight construction potential is not fully exploited because the focus is on the construction.

In recent years, plastics and especially fiber-plastic composites have become more important. Their high specific stiffness (e.g. flexural, tensile or torsional stiffness) and strength make them attractive lightweight materials. They offer a wealth of new processing and design options.

A pioneering technology, which is currently still in development and is primarily intended for vehicle construction, consists of integrally joining sheet steel and solid aluminum parts during the forming process. This would eliminate the need for an additional joining step and load-optimized components could be manufactured quickly and efficiently.

Principles in the design phase

Detailed analyzes of the forces on the component are important for lightweight construction. Loads that are only estimated and assigned safety factors lead to oversized components. Precise knowledge of the loads is essential, especially when calculating stability. Computational methods have made great strides; The ubiquity of PCs with high computing power and better relevant software make it possible to calculate much more today than in the past (see also finite element method ).

Detailed requirements in the burden- or specifications result in minor structures. The dimensioning load cases that a component sees often do not occur simultaneously. If the component is dimensioned for the simultaneous occurrence of all maximum loads, it is robust but not light. The requirements for a component should therefore be checked critically in order to obtain light structures.

Principles in the construction phase

The material lightweight based on the fact to replace the original material of a component with another material with higher specific properties. Compared to conventional steel grades, high-strength steels (“lightweight construction steels”) usually allow lower wall thicknesses with the same component properties. A frequent application in automobile construction is the substitution of a steel sheet with a higher-strength steel sheet, an aluminum sheet or plastic parts (e.g. GRP or SMC ). In the small and medium-sized car segment, weight reductions are worthwhile if they cost up to around € 5 per kg. In the upper class, solutions up to € 14 per kg are accepted, in the luxury class even € 20 per kg (depending on the location in the body).

The constructive lightweight trying to reach the target by lightweight design measures. Primarily, the most uniform possible utilization of the material volume is aimed for. So z. B. parts subject to bending stress are replaced by sandwich solutions or trusses . In principle, an attempt is made to design with as thin a wall as possible. However, this increases the risk of stability failure (buckling, buckling), which makes a precise mechanical analysis necessary. Forces in lightweight structures should be directed directly. Notches usually require additional material and should therefore be avoided. Lattice girders with pure tension and compression rods represent optimal structures in this regard.

The lightweight system does not consider the individual components but the whole system. Functional integration can make a single component heavier. However, the savings through the functional integration make the system lighter, whereby the lightweight construction goal in the system is achieved. System lightweight construction is particularly important for vehicles. The principles of structural and lightweight construction are used for adaptive structures.

The choice of a suitable joining and manufacturing process represents another constructive way. By laser welding for can. B. on the overlap of sheets can be dispensed with. This enables a lighter construction. Replacing riveted connections with adhesive connections is also an effective lightweight measure. Forged components often have a higher fatigue strength than identical welded constructions. They can therefore be constructed with smaller cross-sections.

Principles in the manufacturing phase

The lightweight construction principle can be implemented through tight tolerances , both in the production and in the purchase of semi-finished products. If you allow a thickness tolerance of ± 0.1 mm for a sheet with a wall thickness of 1 mm, the mass of the sheet fluctuates by 20%. Sheet metal with tight tolerances is therefore necessary for aircraft construction.

With regard to the strengths, a material with little variation must be selected for lightweight construction. The designer does not choose the mean value of the strengths, but a strength at which z. B. 90% of all samples are above this. If the strength values ​​vary widely, the component must be overdimensioned in order to be safe from failure.

Lightweight construction in buildings

In the case of dynamically loaded welded structures, such as B. Steel bridges and cranes , taking into account the HiFIT process during development, the construction can be specifically streamlined with the same load level and the same service life.

Most structures are and will be built using solid construction: a form of supporting structure in which space-enclosing elements such as walls and ceilings also fulfill the static load-bearing function. The opposite term is skeleton construction . The latter is related to the column construction . Solid construction also refers to the field that deals with “solid” building materials ( masonry , concrete ). Contrasting terms are lightweight construction and timber construction .

Proponents of lightweight construction (including skeleton construction or timber construction ) justify their preference with the argument of sustainability: Such an approach not only enables the reduction of mass flows of building materials, but also an increase in the amount of regenerable material and energy. The increased use of wood could also have positive effects in terms of a contribution to combating climate change and reducing the amount of waste. For the users themselves, lightweight construction offers advantages insofar as it enables rapid construction progress , maximum usable space and great flexibility. In addition, there are a number of economic arguments in favor of such construction methods.

Critics of lightweight construction mainly cite fire protection-related arguments for their position. Since wood and wood-based materials are flammable, it is assumed that lightweight constructions have a lower level of safety than solid constructions. In the event of a fire, however, the greatest danger comes from the interior fittings: the construction of a building does not matter. Fire brigades have a fundamentally positive view of wood as a building material because of its predictable fire behavior . However, building insurance is often more expensive than comparable solid houses, as the damage per fire is higher.

In Austria, among others, the Bau.Genial platform, founded in 2006, advocates the further development of lightweight construction and the transfer of relevant knowledge. In May 2010, Guholzbau established itself as a platform that brings together clients and contractors in the timber construction sector.

A form of lightweight construction was used in Gothic building structures as early as the 12th century . The extensive breakthroughs in the outer wall surfaces with windows and a reduction in wall thickness and vault dimensions to a minimum allowed the construction of ever higher structures, which also offered a completely new aesthetic than older construction methods.

Related topics

• The lightweight construction can be combined with adaptive structures .
• Material selection

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1. ↑ stahl-online.de ( Memento of the original from January 17, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF). 
2. ↑ auto-motor-und-sport.de: Lightweight construction on the Jaguar XE , accessed on March 17, 2015.
3. ↑ altairenlighten.com: Jaguar Launch New XE Featuring a Lightweight Aluminum Monocoque , accessed March 17, 2015.
4. ↑ Scientists from Hanover develop new lightweight construction process. Retrieved April 26, 2018 . 
5. ↑ afbw.eu  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF).  
6. ↑ Study focus on sustainability. Properties and potential of lightweight construction. (Head of Karsten Tichelmann, publications).
7. ↑ derstandard.at
8. ↑ baugenial.at ( Memento of the original dated June 29, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
9. ↑ Study with a focus on the physical properties of lightweight constructions. (Head of Karsten Tichelmann, Publications), pp. 82–99.
10. ↑ BAU.GENIAL 2015 - the best educational buildings. In: Wohnnet. Retrieved January 14, 2016 . 
11. ↑ guholzbau.at ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.