# Can You Crack the Crush Tube? A Nonlinear Deformation Challenge Problem

Webinar Presentation (PDF)
Webinar Recording (WebEx)
Note: The presentation and recording are only available to NAFEMS members.

### Overview

The Computational Structural Mechanics working group would like to present NAFEMS members with a nonlinear deformation challenge problem. The problem is outlined below, and will be described in more detail in this webinar. We’d love to learn how you would tackle the problem and look forward to comparing approaches.

The design department of your company are engaged in a project to design an impact limiter for a part to be moved by a crane lift. The design they want to go with is for two effectively rigid thick steel plates; the crane lifting points will be attached to the lower plate. The part that is required to be lifted will be attached to the upper plate, and the two plates must be separated by at most 350mm to provide the necessary clearance throughout the lift. The designers have determined that, for the energy content of the maximum credible drop height, a set of tubes that can each provide 100kJ of energy absorption would be sufficient, and they have found some stainless steel tubes in stores that they think will work. The tubes can be cut to the required 350mm length, and there are a large number of tubes immediately available which makes them very attractive to use. Simple hand calculations have shown that these tubes are capable of supporting the static force during the lift, including all credible dynamic loads from the crane.

The tubes have been inspected by the designer using a Vernier gauge and appear to all have a 4.0mm wall thickness, are visually round with no obvious ovalisation or other imperfections, and have an outside diameter of 174mm. The material certification cannot be found, although the company metallurgist has suggested that a mean plastic flow strength of 317MPa has been used in previous work which gave reasonable correlation to crushing problems such as this for this sort of material. The metallurgist is very busy (and also quite grumpy!) and won’t provide any more assistance in characterisation of the material. The designer is also very sorry, but there isn’t any money in the project for testing of the tubular material, either.

The designer wants to know if the tubes that have been found in stores are suitable for use and will absorb the required energy. What is your advice? What caveats, if any, do you think are necessary to be attached to your advice, noting that the project is under considerable time and cost constraints.

Figure 1: The tube and plates.

Responses are encouraged that cover a wide range of simulation approaches to the problem, augmented by existing published solutions where applicable. Innovations in simulation approach as well as efficiency in answering the question are particularly welcome (the ‘design department’ doesn’t have the budget to pay for very large amounts of time in analysis). The responses will be collated by NAFEMS and a summary report of the findings will be made available free of charge to all participants. Particularly noteworthy contributions can be highlighted and the names and affiliations of selected contributors can be included in the summary report, subject to the approval of all parties. There will be an opportunity to question the ‘designer’ to a limited extent (the department is busy after all and just wants answers from you!), and all queries (and their responses) will be made available on the NAFEMS website.

This webinar was available to all NAFEMS members exclusively as part of their membership.