Sudipto Mukherjee

Effect of Active Muscle Forces on Knee Injury Risks for Pedestrian Standing Posture at Low-Speed Impacts

Objectives: The objective of the present study is to investigate the effect of muscle active forces on lower extremity injuries for various impact locations and impact angles for a freely standing pedestrian. Methods: FE simulations have been performed using a validated lower extremity FE model with active muscles (A-LEMS). In all, nine impact orientations have been studied. For each impact orientation, three different pre-impact conditions of a freely standing pedestrian, representing a cadaver, and an unaware and an aware braced pedestrian, have been simulated. Stretch-based reflexive action was included in the simulations for an unaware pedestrian. Results: Strains in knee ligaments and knee joint kinematics have been compared in each impact orientation to assess the effect of muscle activation. It is observed that strain in knee ligaments is dependent on impact locations and angles and the MCL is the most vulnerable ligament. Further, due to muscle effects, except when the impact is on the knee, peak strain values in all the ligaments are lower for an unaware pedestrian than either for a cadaver or for a fully braced pedestrian. Conclusions: It is concluded that active muscle forces significantly affect the knee kinematics and consequently reduce strains in knee ligaments.

Determining the strain rate dependence of cortical and cancellous bones of human tibia using a Split Hopkinson pressure bar

Mechanical properties of tibial bone at compressive strain rates of 50–200/s are obtained through a Split Hopkinson pressure bar. Cylindrical specimens of 12–15 mm diameter and 2–5 mm thickness were prepared. The Youngs moduli are calculated from linear portion of stress–strain curves. For both cortical and cancellous part of the bones, the Youngs modulus was found to increase with the increasing strain rates. Also for both cancellous and cortical bones, the Youngs modulus increases consistently with increase in densities.

Repositioning the Human Body Lower Extremity FE Model

This study aims to develop a methodology to generate anatomically correct postures of existing human body finite element models while maintaining their mesh quality. This repositioning is often done by running dynamic simulations. Such simulations, while taking a lot of time have the disadvantage of giving distorted elements as well as require a lot of expertise and have subjective interventions. Also, the anatomical correctness of the final position, and the kinematics followed during repositioning by dynamic simulations are uncertain. The developed method is based on computer graphics techniques and repositions a joint in just a few seconds. Repositioning of the lower extremity was also carried out using Finite Element (FE) simulations and analysed. The repositioning results from the two techniques were compared and it was found that the technique based on computer graphics gave satisfactory results.

Inverse Finite Element Characterization of Soft Tissues Using Impact Experiments and Taguchi Methods

The objective of this study is to establish a methodology to identify the dynamic properties of soft tissues. Nineteen in vitro impact tests are performed on human muscles at three average strain rates ranging from 136/s to 262/s. Muscle tissues are compressed uniaxially up to 50% strain level. Subsequently, finite element simulations replicating the experimental conditions are executed using the PAM-CRASH, explicit finite element solver. The material properties of the muscles, modelled as linear isotropic viscoelastic material, are identified using inverse finite element mapping of test data using Taguchi methods. Engineering stress engineering strain curves from experimental data and finite element models are computed and compared during identification of material properties at the above mentioned strain rates. Response of finite element models, with extracted material properties, falls within experimental corridors indicating the validation of the methodology adopted.

Optimisation study on multibody vehicle-front model for pedestrian safety

ABSTRACT Ensuring the safety of pedestrians in a crash with automobiles remains a vehicle design challenge. Multibody simulations were developed in MADYMO to simulate a crash of a parametrised vehicle front model (14 parameters) against three different Netherlands Organization for Applied Scientific Research (TNO) pedestrian models (50th %le M, 5th %le F, 6 Y.O. Child). Threat to a targeted pedestrian population was measured using a weighted injury cost (WIC) measure. A pedestrian friendly vehicle profile was obtained using genetic algorithm-based global optimisation to minimise WIC with geometric constraints on vehicle profile. With known limitations, at least one pedestrian-friendly vehicle shape not resembling any existing vehicle profile was found.

Rollover Crash Analysis of the RTV Using Madymo

The Rural Transport Vehicle, popularly known in India as RTV, has a capacity for conveyance of 15 people and runs on compressed nitrogen gas. Incidents of rollover of RTVs have been reported in several cities, including 11 recently reported rollover incidents in Delhi. A full vehicle model of the RTV is developed in MADYMO including steering, tire and suspension. The suspension characteristics were validated using experimental accelerations measured over bumps. A torque controller is simulated to maintain set speed of the RTV in simulations. The model is used to predict rollover limits using Slowly Increasing Steer, J-Turn, and Road Edge Recovery maneuvers. The rollover limits with three different loading states, RTV without passengers, RTV with unrestrained passengers, and the RTV with restrained passengers, have been studied. Comparison with other commercial vehicles indicates that the rollover limiting speed of the RTV in dynamic maneuvers is low.

Modeling of Folding of Passenger Side Airbag Mesh

Airbag as a safety device fitted in automobiles is fast gaining public acceptance. Improvements in design of automobile components, often achieved by computer modeling and simulations, are becoming standards for automobile testing and design. Due to airbags acceptability for four wheeled vehicles, the concept of airbag in motorcycles is now being tested by many [references]. Currently passenger side airbags, which have a larger volume than the driver side airbag, are considered for airbags to be mounted on motorcycles. Modeling of folding of passenger side airbag is a complex and time consuming process. In this work the modeling of folding of passenger side airbag of 160 liter is considered. This airbag mesh is to be used for exploratory simulations of crashes of an Indian motorcycle mounted with an airbag. Commercial software tools used for modeling of airbag folds do not give a realistic inflation process due to large distortion of airbag mesh elements. In this work we use simulations for getting the mesh of a folded passenger side airbag. Unreformed mesh containing six layers of cloth is first generated in Finite Element software IDEAS. This mesh is then exported to PAMCRASH. The fold sequence is then modeled using simulations so as to duplicate the manual folding process. Folds are thus generated in the airbag mesh using simulations in PAMCRASH. For each simulation of folding, the mesh is held between rigid planes and these planes are given velocities corresponding to the folding process. This method of fold simulation is time consuming. But it gives folded airbag mesh of complex shapes. Inflation process of folded airbag mesh is in better agreement with unfolded airbag mesh inflation process.

Response of Tonic Lower Limb FE Model in Various Real Life Car-Pedestrian Impact Configurations: A Parametric Study for Standing Posture

This paper investigates the effect of muscle contraction on lower extremity injuries in car-pedestrian lateral impacts. Three variables, viz. height of impact, pedestrian offset with respect to car centre and impact speed, are considered. Full-scale car-pedestrian FE simulations have been performed using the full body pedestrian model with active lower extremities (PMALE) and front structures of a car model. Two pre-impact conditions of a symmetrically standing pedestrian, representing a cadaver and an unaware pedestrian, have been simulated. It is concluded that (1) with muscle contraction risk of ligament failure decreases whereas risk of bone fracture increases; (2) ligament and bone strains are dependent on the impact location; (3) chances of ligament injuries are higher when the impact occurs near the outer corner of the car; (4) risk of bone fracture increases with speed and (5) bone fracture reduces the risk of ligament failure.

Exoskeleton for Tele-Operation of Industrial Robot

An upper limb exoskeleton is being used as master for tele-operation designed to control KUKA KR5 robot that is not directly accessible. Design and implementation issues for this task have been discussed. The connectivity is through .NET remoting, gravity balancing with springs and compacts solutions for alignments of collocated shafts have been achieved through design.

Experimental Study of Variation between Quasi-static and Dynamic Load Deformation Properties of Bovine Medial Collateral Ligaments

In a significant number of automobile crashes involving pedestrians, the knee ligament which controls the stability of the knee often get severely loaded. In lateral impact on knee during automotive crashes, varus-valgus deformities result in failure of ligament by avulsion or rupture. Varus-valgus deformity strains occur mainly in the middle region of ligament and it is known that properties vary in the different regions of the ligament. Experimental measurement of tensile-load elongation behavior of bovine middle region medial collateral ligament properties between strain rate 0.0001/s to 161/s are reported here. The results shows a linear stress-strain response at lower strain rate whereas it is nonlinear and strain rate sensitive in dynamic loading conditions. The objective of this study is to establish a methodology to identify the quasi-static and dynamic properties of ligaments.