Case Studies

Objective:
To carry out stress analysis of the complete crane structure for strengthening weak areas and weight reduction for maximum rated load condition.

Team : 1 Senior engineer for analysis and required mesh changes in iterations and 2 for initial meshing.

Duration : 1 month

Software Used : Hypermesh and MSC Nastran

Client : Domestic Crane manufacturer

FE Modeling :
HYPERMESH was used to mesh the parts of the crane and the boom tubes using shell elements. Node merging was done at weld location. RBE2 with ends released were used to model the rope and mechanism linkages.

Loadcases:

• Static (stationery with load lifted)
• Dynamic (moving with load lifted)
• Swinging (boom revolving with load lifted)

Analysis and iterations:
Analysis was carried out using MSC NASTRAN and post processing was done using Hypermesh. 5 design modification iterations were carried out to arrive at a safe and weight optimized design.1.5 tons of steel was reduced. This increased their profits in millions and made their product ready for international competition.

Objective:
To optimize the structure of a small car to reduce the intrusion levels at the booster, dash board and A-pillar locations by 20%, 30% and 25% respectively under Offset Deformable Barrier Test.

Team : 1 Senior engineer for analysis and mesh modification.

Duration : 10 days

Software Used : Hypermesh and LS Dyna

Client : Japanese Car Manufacturer

FE Model :
The debugged FE model in LS Dyna format was supplied by the customer. Inflated tires using airbag model and deformable suspensions were present in the model. The Deformable Barrier was also present in the Vehicle model file.

Problems Identified :
The vehicle was propelled with a velocity of 40mph and the analysis was carried out for 120 ms in LS Dyna using a Dual CPU IBM server. The baseline analysis showed that the energy absorption pattern of the crash members was proper but the passenger compartment was week. The under body long member was buckling at a very low load due to small cross section and improper spot welds at the curvature about the toe pan. The upper A-pillar portion and the cant rail areas were also weak.

Solution :
5 design modification iterations were carried out to arrive at the solution that was accepted by the client. The modifications carried out consisted of strengthening the underbody long member and its spot welds to give it a box effect along with the adjoining floor portion. The A-pillar and the cant rail areas were also reinforced. The booster, dash board and A-pillar intrusions were reduced by 17%, 28% and 50% respectively.

Objective:
To optimize the structure of a newly designed 2nd row middle seat of a crossover vehicle. The middle seat was designed by the customer and it was required to optimize the structure to meet ECE-R14, R-17 and R-21.

Team : 1 Senior engineer for analysis and mesh modification in iterations and a team of 2 meshing engineers for initial meshing of complete seat.

Duration : 45 days

Software Used : Hypermesh and LS Dyna

Client : UK based Supplier to DCX

FE Model :
The FE model was created using HM in LS Dyna format. Node to node rigid elements were used to simulate welds. Deformable 50 percentile LS Dyna FE Dummy was used for sled test. The head form for R-21 requirement was a spherical ball of 165 mm dia. and an accelerometer was placed at the center to record the decelerations. Time step was maintained to 0.6 micro sec and scaled mass was kept with 1% of total mass.

Loadcases :

• R14 Seatbelt anchorage test – The seat structure and the seat belt anchorages on the seat and the floor should sustain a load of 13.5KN plus 20% overload pull at the torso and lap belts. The requirement was met in 7 iterations. Major changes were in the cushion and the back side member on the top anchorage side.
• R17 Sled Test (dummy and luggage together) – With the 50% dummy, seat belt and the luggage in place of the floor is given a rearward acceleration pulse which is obtained from full frontal impact test of the vehicle. The requirement is that the seat portions should not move ahead of the transverse plane passing through a point 100 mm forward of the H point. The requirements were met in two iterations.
• R21 Sharp corners and Energy Dissipation (Head Impact) – There should not be any sharp projections with radius less than 2.5 mm. This requirement is visually tested. The other requirement is that the head impacted on the structure should not have decelerations excess of 80g for more than 3 ms. The main area of concern was the top portion of the frame side member that routes the seat belt from the retractor. This area was covered with a metallic and a plastic part for absorbing the head energy. These two parts were optimized in around 5 iterations.

Analysis:
Three load cases were analyzed separately. About 15 over all design change iterations were required to come at the optimized solution. Each run took around 10 hrs to solve. First meshing took around 30 hrs and each setup and debugging took around 10 hrs.

Objective and Background:
An underbody long member of a small car was to be manufactured as a single piece. It was a 3 m long hat section channel having about 45deg up and down bends. Usual stamping process was a difficult task due to the slenderness of the part. A solution to that was stretch bending. The component supplier was not sure whether the part would get formed without tearing and it was a great risk for them to invest on the prototype tooling. So they took our services to get a first cut confidence about the manufacturability of the component.

Team : 1 Senior engineer for analysis and meshing.

Duration : 30 days

Software Used : Hypermesh and LS Dyna

Client : Local Auto Component Supplier

FE Model :
The FE Model was made of shell elements with forming suitable material model. The stress strain curve was obtained from tensile test and the formability factor was obtained from the manufacturers cat log. The tool was modeled with rigid material and forming contacts. Thickness reduction output was taken. A rotating tool was used which rotated the channel around itself forming the bend. Adaptive re-meshing was used. Each run took 8 hrs.

Problems Identified and solution:
The angle was too high which showed tearing at the curvatures, also there was inward sliding of material. The inward sliding was prevented using clamps. The tearing was partially reduced by releasing the end clamp and allowing only a bare minimum stretch to prevent wrinkling. A new material with better formability was suggested to reduce the thinning. The final thickness was from 1.25mm to 0.9mm which is generally acceptable and does not lead to tearing. This material change was accepted by the end customer and the supplier got confidence that the channel would get manufactured and so he went further for prototype tooling.

Objective :
A series of knuckle variants of a platform design already on roads, in passenger car sector, were analyzed to establish the material properties and the analysis method. The same method and material were used for analyzing and optimizing the knuckles of the future variants which were under development.

Team : 2 Senior engineers for analysis and 2 meshing engineers.

Duration : 180 days

Software Used : Hypermesh, MSC Patran, MSC Nastran, MSC Marc and MSC Fatigue

Client : US Based Auto OEM

FE Model :
Second Order Tetra Elements were used with a very thin shell element skin so as to extract surface stresses and to keep the output file small in size. Each knuckle was analyzed for around 40 load cases like forward braking, rearward braking, left cornering, right cornering, bump etc. The test data and field failure histories for the knuckle variants on roads was available.

Analysis :
The static and transient stress analysis was carried out in MSC Nastran and the Life prediction in MSC Fatigue. Load case based static fatigue and acquired transient signal based dynamic fatigue analysis were carried out on old variants and compared with the field failure histories. Fine tuning of material properties and analysis process was carried out and the same procedure was used for the knuckles for the new variants that were in development phase. For load cases with stresses above yielding EN analysis was used and for stresses below yielding SN analysis was used.

Objective :
The folding mechanism of a plastic shelf behind the rear seat was to be optimized. The rear seat was reclinable and the shelf was foldable. When the seat used to push back the shelf while reclining rearwards the shelf used to fold at a plastic hinge and slide forward with the folded portion turning down and moving downwards. The mechanism was guided by a cam cutout in the shelf which used to slide on a pin in the side wall. The cam profile was to be optimized so that the force required for the folding is minimum.

Team : 1 Senior engineer for analysis and mesh modification.

Duration : 7 days

Software Used : Hypermesh, MSC Marc, MSC Adams and Think Design for CAD Modifications

Client : European Tier 1 Supplier

FE and MBD Model :
The cad geometry was obtained from the customer in the form of parasoliod models. The load on the shelf and the stress strain curve of the nylon material was provided by the customer. The folding force was decided in coordination with the customer’s designers. FE model of the shelf was made with shell and solid elements.

Analysis :
First Non Linear FE analysis was carried out in MSC MARC to find out torsional stiffness of the shelf’s plastic hinge. This stiffness obtained was incorporated in the MBD model. About 5 MBD analysis iterations were carried out using MSC Adams to optimize the cam profile so that the folding load is minimum and there is no locking during the folding process. In each iteration the cam profile was changed in CAD software and modified shelf model was imported in Adams.