Computational Structural Mechanics

Our CSM research includes static and dynamic analyses of complex solid bodies using computational approaches such as finite volume, finite element, discrete element, and meshless methods. The focus of this group is on applications involving large strain, high strain rates, and strong shocks occurring in impact events. These applications include hypervelocity ballistic impact and blast simulations for defense and national security, composite body armor systems, vehicle crashworthiness, traumatic injury biomechanics, and sports mechanics. The development of novel algorithms and computational approaches to improve numerical solutions to these challenging problems has been the traditional concentration of this laboratory.

Examples of current research:

  • A Contact Algorithm for Multi-material Hydrocodes

    High strain events such as ballistic penetrations, explosions, and high velocity impacts lead to large scale deformations that present several significant computational challenges. Common Lagrangian finite element methods are not equipped to handle these severe distortions and will often fail for problems of this type. Because of this, Eulerian and Arbitrary Lagrangian-Eulerian (ALE) methods are popular when modeling these extreme loading events. While simulation codes using these techniques can perform well under some circumstances, problems in which sliding contact is important can lead to significant inaccuracies. Traditional Eulerian and ALE codes handle contact between materials by mixture theory, which leads to artificial bonding at the material interface. This approximation has little basis in the physics taking place at the contact boundary and can easily lead to unphysical behavior.

    The ALE hydrocode ALEAS has been developed by researchers in the Computations Structural Mechanics (CSM) group to address a variety of challenges including the sliding contact issue in Eulerian hydrocodes. By solving the conservation equations separately for each material and imposing contact constraints we are able to accurately model the physics taking place at the contact interface. This approach to Eulerian contact is a new paradigm in the simulation of materials under extreme loading conditions. Example applications of this work include accurate analysis of post-penetration behavior for long rod projectiles and frictionless sliding, both of which are impossible to accurately model using traditional Eulerian methods with mixture theory.

  • Improved Football Helmet Design

    Every year more than 1.5 million people suffer a sports related concussion. Current medical research has shown that repeated blows to the head, such as those experienced by football players, can lead to debilitating diseases such as chronic traumatic encephalopathy (CTE) and dementia. However, despite extensive research that has gone into understanding concussion and its long-term health effects, most modern football helmets are not designed to prevent concussion.

    The Computational Structural Mechanics (CSM) group, in collaboration with a multi-disciplinary team from the UAB School of Engineering and the Heersink School of Medicine, has been working towards tackling the problem of concussion in football. Traditionally football helmets have attempted to mitigate linear accelerations and prevent skull fracture, while doing little to address rotational accelerations. However, current research has shown rotational accelerations are the likely source of strain-related injuries that lead to concussion.

    Through the use of advanced finite element modeling software, the CSM group has developed a helmet design that decouples the motion of the outer shell of the helmet from the player's head during impact. This design uses an impact liner consisting of energy absorbing columns that buckle to absorb the energy of direct impacts while bending to reduce the severity of rotational impacts. Our research has shown that this design can reduce the rotational accelerations experienced by the player's head by as much as 35% for a severe hit scenario. Stated in an alternative way, a hit that would result in a risk of injury of more than 90% for a traditional helmet would have less than a 10% risk of injury using the helmet design based on our modeling.

    Through the use of advanced finite element modeling the CSM group is working to make it so the next generation of athletes will not have to face the choice of playing the game they love or dealing with the long-lasting consequences of concussion.

  • Analysis of Vehicle Impact on Guardrail End Terminal

    Every year almost 7 million people are involved in motor vehicle crashes on America's roadways, and in many of those accidents guardrails and other barrier systems play a vital role in saving the lives of the people involved. The Computational Structural Mechanics (CSM) group at UAB uses state-of-the-art finite element software to simulate real-world impact events in order to reduce the risk and severity of injury in these crashes.

    Working alongside other researchers in the UAB School of Engineering, the CSM group uses finite element modeling to gain a better understanding of system behavior and identify critical areas of weakness in designs before physical testing occurs, thereby resulting in reduced design time and development costs.

    According to data from the National Automotive Sampling System - Crashworthiness Data System (NASS-CDS), crashes into guardrail end terminals carry a 5.1 times greater risk of injury than impacts at other points along the guardrail face. By designing guardrail terminals that absorb the energy of the impact and slow the vehicle gradually the risk of severe injury is reduced significantly. The CSM group uses computer modeling to develop guardrail terminals that safely and cost-effectively reduce the risk of injury to vehicle occupants.

    In addition to guardrail terminals and end treatments, the CSM group has been actively involved in the development of self-restoring crash cushions, impact barrier systems and bollards, and a variety of other highway safety applications.

  • A Mesoscale Model for Geomaterials
    Mesoscale model.

    Geomaterials, such as sand, differ from other common engineering materials like metals, polymers, and many composites, in that the fundamental evolution of the underlying structure may reasonably be considered to occur at a higher scale, i.e. at the mesoscale rather than the microscale. This offers a somewhat unique opportunity to be able to characterize the underlying structural evolution of the material, and use that characterization to inform a general constitutive framework to model the behavior of a wide spectrum of soils under a range of pressures and distortional transient loading conditions. This research project explores internal evolution of a sand using mesoscale simulations of the physics involved. The mesoscale modeling is carried out using the Discrete Element Method (DEM).

    The DEM is calibrated to experimental data using mathematical optimization for statistical ensembles, a novel framework developed specifically for this project. Hundreds of thousands of simulations of the calibrated DEMs at the mesoscale are used to carry out a homogenization study of the granular subdomain. This is done for three distinct purposes: 1) to identify the threshold at which the transition from discrete mesoscale to the Representative Volume Element (RVE) occurs, 2) to quantify the uncertainty associated with discretization below the RVE threshold, and 3) to supplement the experimental dataset with quasi-experimental statistical results from the physics-based particle simulations with the DEM.

Questions?

For more information, please reach out to David L. Littlefield, professor and Chairman of the Department of Mechanical Engineering, at This email address is being protected from spambots. You need JavaScript enabled to view it. or 205-934-8460.

Current Staff and Student Members

Kenneth C. Walls
Scientist I, Department of Mechanical Engineering

Gerald M. Pekmezi
Ph.D. student, Interdisciplinary Engineering

Shannon L. Lisenbee
Ph.D. student, Interdisciplinary Engineering

Parth Y. Patel
M.S. student, Mechanical Engineering

Kevin E. Franks
M.S. student, Mechanical Engineering