Design for weight optimization


Historical dependency

The revolutionary invention and evolution of the wheel is a clear gauge of technological advancement of a civilization. Without this revolutionary invention, modern society and growth would be limited if not stalled. Transportation is one of the driving forces of today’s economy, making the wheel a critical instrument. Safety and fuel consumption standards are motivating advanced manufacturing and material sciences to further optimize wheels. Although there are probably many factors that are propelling wheel evolution, the factor at the top of the list is durability. A few hundred years ago inventors realized that normal strength assessment methods did not apply well to structures with repeated loading such as wheels. This realization gave birth to the first systematic fatigue investigation that was done between 1852 and 1870 by a German engineer named August Wohler.

Technological progress

Jumping forward to 2017, material sciences, advanced manufacturing, and analytical tools have helped Accuride Corporation develop highly engineered aluminum and steel wheels for the commercial vehicle industry worldwide. Fatigue and durability testing have become the primary design drivers for wheels. Advanced understanding of fatigue analysis and testing capability is needed in order to achieve optimized designs. Accuride has relied on nCode software from HBM Prenscia to provide the tools to reach their design goals.

Just like the evolution of the wheel has been fueled by the evolving needs of society to increase efficiency and safety, our society has now added the new drivers of energy efficiency and environmental impact while continuing to meet the expectations of prior years.

Design change validation

Accuride Corporation (originally Firestone Steel Products) has been in the wheel business since 1905 and is answering the continual needs of its customers and the commercial trucking industry for technological advancement to carry larger loads while using less fossil fuel. While offering weight savings and lower rolling resistance, Accuride ensures that those changes do not compromise the safety and integrity of the wheel. The new designs are subjected to reliability testing that goes above and beyond industry standards including straight rolling of a wheel and tire assembly and rotating bending tests. Accelerated testing is done at elevated loads to a specified number of cycles. Due to the potential variability in testing, Accuride significantly exceeds industry standards despite the financial and time demands of physical testing. For every prototype design that is tested, custom-built tooling and manufacturing processes must be developed to generate sufficient samples for design validation. Prototype builds and testing can take weeks and even months. If samples do not pass the qualification testing, then a new design iteration is started and the clock is reset for samples and testing, thus prolonging product release. Therefore, minimizing design iterations is critical in managing development costs and time-to- market goals.
Testing bench used to gather data on straight rolling and bending stress conditions

Targeted tests guided by simulation data

In order to meet both customer’s weight restrictions and reduce testing costs, Accuride relies on nCode software products to provide the tools to reach the company's design goals. "We use nCode DesignLife software to ensure durability is achieved in the shortest amount of time by reducing the number of prototypes submitted for testing. DesignLife helps us streamline the CAE design process by allowing us to simulate realistic loading conditions to minimize costly design changes. The software helps us identify critical locations and calculate a realistic fatigue life by correlating CAE directly with the physical test data collected."
Accuride is able to perform more targeted physical tests by simulating the real usage environment and predicting structural performance directly from Finite Element (FEA) results. The need for prototype testing has been reduced, which lowers design costs. Measured time series and predicted strain data is used for fatigue analysis and development of FE loading models. DesignLife is then used to analyze new designs compared to anterior models in pre-conception stage to avoid over-design. The use of DesignLife helps reduce costs and weight by enabling the evaluation of more design options in the early conceptual stage.

Customized analysis process saves time and resources

A unique feature in steel wheels is the presence of an assembly seam weld. Weld features are notorious for being fatigue weak spots in a design if not manufactured to the highest standards. Accuride uses the DesignLife Seam Weld option to evaluate the potential fatigue performance of seam welded joints in steel wheel designs. The module simplifies the design process by following well accepted weld analysis methods in a streamlined manner.
Accuride also uses the Strain Gauge Positioning option to calculate the optimum position and number of gauges needed. Strain gauges measure the actual physical strains, but actual usage environments can be extremely complex. Proper placement of strain gauges is key to correlation between mathematical loading models and actual driving conditions. By applying some reverse engineering, loading models can be developed to accurately replicate strain fields created from actual usage loading. The analysis environment can also easily be customized, including the ability to evaluate multiple load cases simultaneously.

Software customization environment

During a crucial point of the design process, Accuride requires a tool capable of handling large amounts of datasets. nCode GlyphWorks is the necessary tool used to compress this huge amount of data. GlyphWorks is a powerful data processing system for engineering test data analysis with specific application to durability and fatigue analysis. It provides a graphical, process-oriented environment designed to create a workflow by dragging and dropping blocs to represent the process graphically. The software provides a wide range of data processing capabilities with specialized options such as fatigue analysis, accelerated testing and frequency domain tools for ride quality analysis.

Accuride states, "Computer modeling reduces our time to market as well as reducing developing costs and testing times. Using nCode software, we are able to pinpoint any stress points and fracture of each design by identifying high stress areas; those areas can be addressed and targeted more specifically during testing to ensure the robustness of the new design."

nCode helps Accuride analyze complex biaxial wheel test data

FEA and other numerical methods are heavily used to evaluate new designs. These methods significantly help to reduce product time to market. However, these analysis methods can at times use significant resources. To predict the fatigue life of a wheel, you must understand the strain history in the wheel through at least one revolution. Sometimes, incrementally loaded models can be used, but require multiple load cases FE solutions for each loading direction. For example, a wheel with 10 hand holes might require 20 load cases for each design iteration to obtain the necessary strain history used as input to fatigue predictions. Accuride explains: "We collaborated with nCode to develop methods for achieving the same strain history with only 2 FEA solutions saving roughly 10x in the FEA solution times. This achievement is possible by leveraging the symmetry in the geometry of the part even though the loading does not share the same symmetry."

Accuride follows industry design and test standards set by the Society of Automotive Engineers (SAE). In North America, SAE has established two basic tests for evaluating wheels on commercial vehicles. These tests include a straight rolling with a tire, and a rotating bending test without a tire. Accuride states that: "Historically, these tests have served the industry very well. In many other parts of the world the basic SAE tests are also used, but a more complex biaxial test is becoming the standard." A biaxial test is capable of applying radial and lateral loading simultaneously in a series of complex loading patterns, resulting in a more representative loading experience.

Accuride describes its continued partnership with HBM Prenscia: "As Accuride becomes a global player in the commercial wheel market, we are not only learning to do biaxial testing, but also to predict fatigue performance prior to testing on this more complex test. nCode has played an important role helping to develop and implement enhanced performance predictive methods, saving Accuride countless hours of product development time."

"The decision to move forward with design changes is a positive one. We are now convinced that the approach we took worked. We've had success and we recognize that working with nCode is one contributing factor of the success of our product development to optimize wheels while maintaining durability and safety. This has been a positive contribution to our success."

Mike McLeod - Accuride