Updated: May 28, 2022
Before we start fabricating any automobile, the first thing is material selection. This will be based on certain important factors such as:
Why should we consider Lightweight Materials for Automobiles?
Advanced materials are essential for boosting the fuel economy of modern automobiles while maintaining safety and performance. Because it takes less energy to accelerate a lighter object than a heavier one, lightweight materials offer great potential for increasing vehicle efficiency.
A 10% reduction in vehicle weight can result in a 6%-8% fuel economy improvement. Replacing cast iron and traditional steel components with lightweight materials such as high-strength steel, magnesium (Mg) alloys, aluminum (Al) alloys, carbon fiber, and polymer
composites can directly reduce the weight of a vehicle’s body and chassis by up to 50 percent and therefore reduce a vehicle’s fuel consumption. Using lightweight components and high-efficiency engines enabled by advanced materials in one quarter of the U.S. fleet could save more than 5 billion gallons of fuel annually by 2030.
By using lightweight structural materials, cars can carry additional:
Advanced emission control systems
Integrated electronic systems
All without increasing the overall weight of the vehicle.
While any vehicle can use lightweight materials, they are especially important for hybrid electric, plug-in hybrid electric, and electric vehicles. Using lightweight materials in these vehicles can offset the weight of power systems such as batteries and electric motors, improving the efficiency and increasing their all-electric range. Alternatively, the use of lightweight materials could result in needing a smaller and lower cost battery while keeping the all-electric range of plug-in vehicles constant.
How VTO works to improve the Materials:
Increasing understanding of the materials themselves through modeling and computational materials science
Improving their material properties
Improving their manufacturing
Developing alloys of advanced materials
In the short term, replacing heavy steel components with materials such as
Steel, aluminum, or glass fiber-reinforced polymer composites can decrease component weight by 10-60 percent. Scientists already understand the properties of these materials and the associated manufacturing processes.
Uncertainty about future costs is inescapable because of the uncertain rate and direction of future technological progress, as well as uncertainties about the future prices of materials, energy, labor, and capital. Although technological change is certain, its direction, magnitude, and impacts on cost are difficult to predict. For most components, manufacturing costs tend to decrease with increased production volumes and with the accumulation of experience. However, there are no exact methods for predicting future rates of learning by doing or technological progress. Assuming no technological progress or cost reduction via learning will likely overestimate the costs of compliance. On the other hand, overly optimistic assumptions will result in underestimation of costs.
Cost includes three components:
Actual cost of raw materials
Manufacturing value added
The cost to design and test the product
Aluminium and magnesium alloys are certainly more costly and require much energy in the mining and refining processes, than the currently used steel and cast irons. Since cost may be higher, decisions to select light metals must be justified on the basis of improved functionality. Meanwhile the high cost is one of the major obstacles in use of the composite materials.
The importance of some of these factors in the model can be described as follows:
The Resource Depletion Index (RDI):
This index is used to examine the global reserves and the annual consumption rates of certain resources using quantitative measures such as annual mining capacity and total declared global reserves.
Water Pollution Index:
This index represents any chemical or foreign substance contamination into water that is detrimental to human, plant, or animal health by measuring the amount and toxicity of waste water used during the entirety of the vehicle’s lifespan (from the cradle to the grave).
Life Cycle Assessment (LCA):
The LCA is the most-used metric in eco-design. In an LCA, proposed design/material combinations are assessed from energy and emission perspectives over the product’s entire lifecycle.
Retired or end-of-life vehicles usually undergo one of three scenarios. First, in a landfilling scenario, the whole vehicle or some of its parts are completely disposed in a designated area of a landfill. This strategy is not preferred, as it adds environmental burdens such as contaminations of surface and ground water and loses of the usable land. Second, some vehicle parts (e.g. Body parts and electric components) may be recovered and reused, for
example, by junkyards. Finally, a vehicle’s major parts may be recycled. In this study, we used the percentage recycle fraction (ψ) as the main metric of recyclability.
When a consumer decides not to use a vehicle anymore, there are following options available:
Sell the whole vehicle to another user.
Disassemble the vehicle.
Remanufacture the vehicle.
Recycle the vehicle for materials.
Dispose the vehicle to a landfill.
This parameter can either be classified under environmental or economic factors. Nonetheless, durability in sustainability design overlaps all economic, environmental, and societal factors, thus enhancing its versatility. Here, we link durability to environmental factors because of the strong, direct relationship between durability and the replacement or reuse of retired parts. For example, composite-intensive body-in-white (BIW) auto bodies are considered less durable in terms of ultraviolet (UV) resistance than steel BIW auto bodies.
Economic Impact Factors:
These represent the costs associated with each lifecycle phase to provide automakers with a comprehensive financial analysis of a given BIW design.
Two metrics are used to quantify societal factors. First, safety is an indirect measure for material properties (i.e., toughness and yield strength). Second, health and wellness are other indirect measures that is governed by:
Noise-vibration-harshness performance (which is controlled by dynamic stiffness of BIW structure and damping capacity of joints and material)
Environmental emissions and ancillary adverse effects (e.g., acid rain, global warming potential, and ozone depletion).
This is the fourth pillar of sustainability model for auto bodies. The goal of adding this extra pillar is to highlight the importance of manufacturability (e.g., formability, weldability and joinability, paint ability) and technical requirements within the initial design process (i.e., at the conceptual design stage) by incorporating both material selection and manufacturing process selection. With such criteria, designers can clarify “what if” analyses (e.g., what if material X is used rather than material Y).
Some sustainability factors are qualitative in nature. For example, materials are classified as having high, medium, or low corrosion resistance. Similarly, fatigue resistance and wear resistance can be expressed qualitatively (an example of these scaling is shown in Fig. 8 for scaling strong, wear resistance materials). Moreover, with the absence of a well-established scientific method to quantify societal factors (i.e., safety and health and wellness), scaling may represent a good way to rank candidate materials in terms of performance.
Safety can be expressed in many ways; in this study, we define safety from a material selection perspective as the material property that plays a role in determining crashworthiness if a vehicle is involved in any accident including minor crashes.
By doing so, safety is assumed to have strong relationship with yield strength and the material toughness.
Similarly, health and wellness can be defined as the material characteristics that interfere with human health and quality of the air.
A simple function of health and wellness should include the amount of emissions released to the environment from cradle to grave (i.e., in all mining and manufacturing processes involved in production and use of the vehicle, and ultimately the recycling or landfilling of the retired parts made from these materials).
Technical factors (i.e. forming, joining, and painting) were also added to the classical sustainability pillars to account for manufacturability of different materials considered in the complex material selection problem.
Unfortunately, these technical factors have neither well-established material selection indices nor any material selection charts that designers can use for screening and sorting purposes. For these reasons, we propose using a scale of five classes (very poor, poor, average, good, and very good) to evaluate the performance of materials from the manufacturing perspective.
Materials which are used nowadays:
An automotive body depends on the manufacturer's considerations with the legislation and regulation, and some on the requirements of the customers. Most of the manufacturers prefer featured materials which are lightweight, economic, safety and recyclability.
The main elements of selecting material especially for the body is involved in a wide variety of characteristics such as thermal, chemical or mechanical resistance, manufacturing efficiency and durability.
Steel stands as the first choice for manufacturers with all the required characteristics. The improvement or development in the steel industry made the steel stronger, lightweight and stiffer than the earlier.
Steel includes not only vehicle bodies, but also engine, chassis, wheels and many other parts. Iron and steel develop the critical components of structure for the bulk manufacturing of vehicles and are low-cost.
The best reason for using steel as a body structure is its natural capability to absorb the impact energy produced in a crash. Low-carbon sheet steel in the thickness of (0.65–2) mm managed to reduce the overall weight of the car and increase the rigidity of the body.
Types of Steel for Car Bodies: