Development of underwater housings for the deep sea made of ultra-high performance concrete (UHPC) and long-term testing at the Arctic Sea
The aim of this research is the design and analysis of underwater housings made of ultra-high performance concrete (UHPC) within the Helmholtz Alliance “ROBEX” (robotic exploration of extreme environments) [1]. Due to the extremely corrosive maritime environment, mainly expensive materials such as titanium, ceramics, special stainless steel and aluminum are used so far for the construction of temporary and permanent research stations to guarantee long-term deployment. In this project the suitability of high-strength concrete with compressive strength up to 210 MPa for underwater pressure housings and constructions is examined to provide a low cost and durable alternative especially for large housings in future.
Experimental and nonlinear numerical analysis of underwater housings for the deep sea, made of ultra‐high performance concrete
The paper describes the design and analysis of underwater housings made of ultra‐high performance concrete (UHPC) within the Helmholtz Alliance “ROBEX” to provide cost‐efficient alternatives to expensive titanium housings. The research is related to former investigations on spherical and cylindrical shells under hydrostatic pressure made of normal strength concrete, performed from 1960 to 1980 at the Civil Engineering Laboratory, Port Hueneme, California. Several housings made of UHPC have been manufactured and the short‐term implosion resistance has been determined experimentally. Since neither the mechanical equations for thin‐ or thick‐walled shells nor the empirical equations for implosion pressure of shells made of normal strength concrete by Albertsen can describe the behavior sufficiently, two nonlinear material laws for concrete, multiPlas Law 9 (modified Willam–Warnke model) and Law 14 (Menetrey–Willam model) by Dynardo for ANSYS, have been calibrated with results from uni‐ and biaxial strength tests, and the results of nonlinear finite element model with ANSYS 16 have been compared. To study the long‐term behavior, an in situ test is currently being performed at 2,500‐m depth in the Arctic Sea.
Material Behavior of an Ultra-High-Performance Concrete Forming Die for Sheet Metal Hydroforming
New sheet metal forming technique and low cost forming die development has resulted from economic requirements and an increasing number of part variants. To form detailed and uniform sheet metal contours in the range of elastic material behavior of the die material, these dies have to withstand approximate pressures of 100 MPa (14.50 ksi) for sheet metal hydroforming. A promising approach to cost-efficient die production is ultra high performance concrete (UHPC) use, particularly for high pressure sheet metal hydroforming. Uniaxial and triaxial compressive stress state stress-strain behavior was investigated through experimentation at various ages for a fine grained UHPC. Three concrete cylinder confinements were additionally tested to achieve a multiaxial stress state. After fabrication of a forming tool prototype, its performance was analyzed in applying a fluid pressure up to 90 MPa (13.05 ksi). The formed sheet shape accuracy and ultimate prototype load were examined. There was also determination of the friction coefficient between sheet metal and concrete. Forming tests have demonstrated that the investigated UHPC can be successfully used as sheet metal hydroforming die material.