More LS-DYNA® Projects
A Summary of Additional LS-DYNA Projects
Shock Fixture Tooling with LS-DYNA: The client faced a difficult problem to validate samples of a delicate electronic device that would be subjected to a small explosive fuze. Prior methods involved the sacrifice of an expensive production part to validate each electronic device. Analysis work was first conducted to simulate the explosive shock pulse of the fuze. This was then validated against experimental work. With a calibrated shock pulse, a novel fixture design was developed that allowed the simultaneous testing of eight electronic devices with a single fuze. This result allowed the client to significantly cut their QA costs and speed up the manufacturing process.
Power Spectral Density (PSD) Analysis, Separation Shock and Pyro Shock: A finite element model was constructed to simulated a broad range of military transport conditions (captive carry), launch (separation shock) and delivery (Pyro Shock) following MIL-STD-810e with reference to Method 514.4 and 516.4. The model was analyzed via PSD and Response Spectrum analysis modes. A fully non-linear transient model (LS-DYNA) was used for the separation shock analysis. Results from this work were used to validate the design of a critical piece of military armament.
Drop Testing of Advanced Composite Satellite Terminal Receiver: Full scale drop testing was done of a lightweight composite satellite receiver. Experimental drop testing had shown failures in three key components. A drop test model was constructed using Femap and then analyzed using LS-DYNA. Two of the three failures were perfectly replicated with the FE model showing that the third part should never have failed. Metallurgical examination showed pre-existing casting flaws that had caused the part to prematurely fail. The structure was optimized with a complete redesign of one part from aluminum to a graphite composite structure. The engineering report for this project was submitted for external review by an opposing team of consultants per U.S. Military requirements.
Electron Beam Weld Simulation in AlBeMet 162: This project arose due to significant weld induced cracking of thick section (25 mm) high aluminum content beryllium materials (60% Be / 40% Al). In the client's welding process, the electron-beam would make multiple passes over the same spot to create a vacuum tight weld zone. Due to geometry constraints and EB energies, cracks would occur near the end of the welding process. LS-DYNA was used to simulate this process and was able to accurately predict cracking in the client's product. The FE model used a traveling energy source that was tuned for the electron-beam welding process. The FE model was able to weld distinct blocks together and also to incorporate welding chills as needed. As the structure cooled down subsequent to welding, residual plastic strains would occur and drive the formation of high elastic tensile stresses. Good correlation was shown between these high tensile stress locations and cracking damage in the part. The welding process was then modified in the LS-DYNA model and it was shown that these elastic stresses could be significantly reduced. Final laboratory work by the client confirmed these numerical results.
Elastic-Plastic Deformation of BGA Lead-Free Solders for Electrical Connector Evaluation: BGA chips by their design use small lead balls to make the final electrical connection to the printed circuit board (PCB). To test these chips, an electrical circuit must be made from the tester to the lead ball. However, it is often a bit more difficult than it sounds since the lead ball must be plastically deformed sufficiently to break through a thin oxide layer and create a robust, low-impedance electrical circuit. This type of mechanical interaction was simulated using LS-DYNA. A Be-Cu spring was pushed against the BGA such that the edges of the spring connector would cut into the lead ball. For this simulation, a lead-free solder composition was used. Simulation results showed that high forces would be required to create sufficient plastic damage on the surface of the lead ball. Given the requirement to simultaneous test hundreds of BGA connections during each test, the force requirements were deemed excessive and the project was cancelled. It should be noted that experimental work using micro-load cells nicely correlated the LS-DYNA results.
Drop Testing and Firing Simulation of an Infra-Red Targeting Scope: Objectives for this analysis work were to determine if the cast magnesium casing would crack upon drop testing onto plywood from three feet and to evaluate the integrity of the internal electrical components and focusing mechanisms during a live firing event. Both models were built with Femap and analyzed using LS-DYNA. The drop testing model was rather simple with the Mg casing modeled with plate elements and the internal components such as lenses, battery pack and circuit boards modeled simply to capture the right center-of-mass and stiffness behaviors. The drop test model accurately predicted that the infra red scope would pass the drop test. The live firing simulation was much more complex and was driven by structural component failures within the scope during the shock event. The LS-DYNA model was able to pin-point the damage mechanism but the actual solution involved a number of fixes that are too lengthy to detail in this brief note. For example, printed circuit board flex (PCB) during the firing event was one failure mechanism that was corrected through the use of additional support pins but a complete internal revision was eventually required.
Compressive Buckling Load Limit for a Large Glass Sphere for Deep Diving Manned Submersible: Engineers that know something about the mechanics of materials realize that high-quality glass is one of true material wonders of the world. Under pure compression, glass can elastically withstand stresses up 500,000 psi and fused silica in excess of 1,000,000 psi. The challenge to engineering with glass and other brittle materials is to maintain the structure under compressive loading. Brittle structures do not fail due to shear loading or pure KIIc fracture growth. In all documented cases of catastrophic failure of brittle structures some sort of tensile stress existed in the structure to start the crack. In hydrostatic loading conditions due to water pressure, most submersible structures are dominantly under pure compressive stress. However, due to openings in these structures via nozzles or hatches, the continuity of the structure is breeched and low level tensile stresses can developed. This problem was eliminated in a unique design proposed by DOER Marine. A 68" glass sphere would have a diametrically opposed 16" openings drilled into the sphere. These openings would act as entry hatches for the three person crew. During operation, a ceramic or titanium plug would provide stress continuity between the glass sphere and the hatch. This design was validated using LS-DYNA to determine its ultimate buckling load. The material model was designed to fail at tensile loads of 500 psi and initiate plastic deformation at 500,000 psi (the start of densification of high purity glass). The wall thickness of the sphere was tapered from 4" at the hatch to 2.5" at the equator. The final tweak for the buckling analysis was to perturb the mesh to account for manufacturing tolerances and localized dimensional imperfections of the sphere. LS-DYNA has a unique approach (*PERTURBATION) where the nodes can be shifted via a number of functions or just in a spectral manner. To bracket the analysis, the sphere was assumed to be out-of-round by 1.0". The sphere was shown to buckle at a dive pressures of around 60,000 psi. At the depth of the Marianas Trench, the sea pressure is 16,570 psi (a depth of 35,798 ft). A fracture mechanics study was also done on the proposed glass sphere to consider sub-critical crack growth around embedded inclusions. Given the overwhelming compressive stress field during operating, no crack growth would be predictive. These findings were confirmed by external experts hired by DOER Marine. The project was halted in mid-course due to a lack of funding by external sources.
Drop Testing of Large Nuclear-Waste Containers: The U.S. Department of Transportation (DOT) specification 49 CFR 173 calls out a rigorous series of testing procedures for containers that are used in the transport of hazardous waste. One such requirement is that the container survive a drop test from a specified height as determined by the weight of the container. As the weight of the container increases, the drop height decreases. As an example, a 50,000 lbf container must survive a drop from 12" onto its most vulnerable corner. Over the years, as the sophistication of computer programs has increased and the accuracy of the real world simulations has improved, the DOT has allowed the substitution of conservative numerical results for actual drop testing. A numerical standard in the industry for drop testing is LS-DYNA from LSTC (see www.LSTC.com). This explicit/implicit FEA code is quite amazing in its ability to accurately capture extreme nonlinearities in a transient event. Although its bread and butter is the simulation of car crashes, the drop testing of large steel containers and the high speed impact analysis of cars are quite similar. Both involve dynamic events where multiple contacting surfaces must be handled quickly and large plastic strains dealt with in a realistic manner.
Large Strain Flexibility Analysis of Nylon 12 Watch Band: Engineering plastics can be divided into two broad camps: high-strength, low-flexibility (e.g., Polystyenes, PMMA) or low-strength and high flexibility (e.g., rubbers, polyamides). LS-DYNA is well suited for the modeling of any type of plastic due to its capability to handle almost any type of material constitutive behavior. In work for a major sports equipment manufacture, a series of Nylon 12 watch bands were analyzed through a complete set of movements that simulated the putting on and taking off of the watch band. The material model for Nylon 12 used LS-DYNA's *mat_simplfied_rubber/foam and was constructed using vendor supplied compression and tensile data. The performance of the watch bank was simulated and checked for fatigue damage. The client accepted the results and put the product into major production.