Introduction

Formula Student Germany is a student engineering design competition in which student teams design, manufacture, test and race their own formula style race-car. This project was a part of working for the team - Orion Racing India.

Suspension is one of the most vital systems of a vehicle. It almost entirely influences the vehicle dynamics and driving characteristics of a car. It is crucial for such an important system to be reliable and robust. However, the system must remain lightweight as adding weight directly affects the performance of a race-car.

Project Report

Goals

The linkages that connect the wheels to the chassis are A-arm linkages and are literally A-shaped, hence the name. We can make them out of composite materials like carbon fiber which would make them reliable, robust and at the same time reduce lap times in the process.

The goal of the project was to design and test a newer lightweight design of suspension A-arm linkages made out of composite carbon fiber material.

Work Done

The design process for the A-arms commenced with the selection of suitable tubes, followed by the design of inserts. These inserts provide support to the tubes either from the inside or the outside, depending on the specific design requirements. The subsequent step involved the careful selection of an adhesive, as it is considered to be the weakest point or potential point of failure.

The choice of adhesive was made after thorough evaluation, considering factors such as availability, cost, strength, and reviews from FSAE forums. Epoxy adhesives, namely E-120hp and 9466 hysol, were ultimately selected for testing and application due to their compatibility with bonding metal with fiber.

To determine the forces acting on the A-arms, a self-developed MATLAB calculator was employed. Forces were calculated for two specific conditions: 1.3g braking and 3g bump force, with the braking condition resulting in the maximum forces on the arms. The loading conditions were chosen based on the car specifications and the characteristics of the competition track.

Results

For the analysis of the A-arm housing, Ansys software was utilized. Aluminum 7065-T6, known for its superior strength compared to pure aluminum, was selected as the material. The first step in the analysis process involved meshing, where different edge lengths (0.21, 0.18, and 0.15 mm) were simulated. After considering computational efficiency and obtaining acceptable results, an edge length of 0.18 mm was finalized.

Additionally, a simulation model of the assembly was created to analyze the load distribution on the A-arms. In order to validate the results obtained from the model, a simplified model based on Universal Testing Machine (UTM) testing was developed. These results were cross-checked through hand calculations to ensure they fell within an acceptable margin of error. Furthermore, UTM testing can be conducted to validate the accuracy and reliability of the simulation model.

The main part to be analyzed is the glue layer which has about 25 MPa of stresses developed in it. However, maximum shear stresses reached are about 15 MPa. Since all properties can’t be exactly predicted with simulations, the model was verified with actual testing. For this a different UTM housing insert was made with similar parameters. This model also helped test for surface preparation.

The results were obtained for varying bond gap after testing on a standard UTM. Surface preparation methods like sandblasted as well as roughened inserts for various bond gaps were tested. The results obtained were as shown in the figure below.

Experimental investigations were conducted to assess the effects of varying bond gaps on the performance of the adhesive joint. Standard Universal Testing Machine (UTM) tests were carried out, with different surface preparation methods employed, including sandblasting and roughening of the inserts. The obtained results are presented in the figure below, showcasing the relationship between bond gap and joint strength.

To evaluate the overall impact of the new suspension control arm design on performance, IPG Carmaker software was utilized. This allowed for the calculation of the time delta resulting from the weight reduction achieved with the updated design across all events at the FSAE competition. The recorded times for each event were compared between the original weight configuration and the reduced weight configuration.

The Formula Student Germany endurance track was used to assess changes in lap times during the endurance event. Initially, a simulation was conducted using the original weight configuration, followed by another simulation using the reduced weight configuration.
The table below displays the lap times for both designs, along with the calculated time delta resulting from the design change. Although the observed time changes may appear minor, if we consider the corresponding points gained or lost across all events due to these time variations, it justifies the decision to switch to CF based links.

Introduction

Goals

Work Done

Adhesive Strength E-120HP

Adhesive Strength 9466 Hysol

Suspension Loads

Results

UTM setup

Bond gap vs Failure Load

FSG track

Laptimes

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