Fig. 1. Titanium is used in a wide range of applications due to its unique combination of properties.
In today’s economy, materials testing can actually save money. Take for instance the aerospace industry. With today’s cost of fuel reaching record highs, you can be sure the aerospace industry is feeling the pinch. The cost per gallon of jet fuel can be calculated at the cost per barrel, multiplied by two, multiplied by 10%. A Boeing jet traveling from New York City to Los Angeles uses approximately 7,760 gallons of fuel! A recent airline-industry study shows that by eliminating approximately two pounds per airplane seat, there is a savings of 9,000 gallons of fuel per year. These statistics place a significant importance on finding new materials to maintain strength as well as reduce the weight of jet aircraft. This is just one of the many uses of titanium. In light of the ever-increasing cost of petroleum-based products, there are sure to be more applications that follow.
Applied Test Systems, Inc. (ATS) has had the privilege of working with some of the world’s greatest minds, learning along the way the importance of a true scientific approach to testing the characteristics of material properties. ATS was recently honored with the opportunity to provide a materials-testing solution for a unique application where the collection and analysis of titanium-material changes at an elevated temperature were required.
There are only a handful of titanium producers in the world, and the promise of the use of this material for a multitude of products and applications has shown to be beneficial at various levels. The strength characteristics of titanium as well as its lightweight properties make it an optimal material for the aerospace industry. The strength-to-weight ratio and resistance at extreme elevated temperatures are major benefits.
As much as 60% of the material weight of a jet engine is produced of various titanium alloys. In addition, the corrosive properties and ease of fabrication of this material offer even more possibilities. Not only is the research for testing raw titanium important, research is also required when the characteristics of titanium are changed.
Titanium is a common alloying agent for aluminum, molybdenum, manganese, iron and a host of other metals. Titanium is as strong as steel but 45% lighter. Although titanium is 60% heavier than aluminum, it is twice as strong and is also compatible with composites, unlike aluminum.
The Superman of Metals
Titanium’s physical qualities of high strength, toughness, durability, low density, corrosion resistance and biological compatibility make it useful in a variety of applications. In the 1940s, it was first used by the space and defense industries. Today, titanium is used in aerospace applications, automobiles, prosthetics, buildings and sporting equipment (Fig. 1).Titanium is a paradox. Supplies of pure titanium are rare, though titanium ores such as ilmenite and rutile are very common. There is more titanium in the earth’s crust than there is nickel, zinc, chromium, tin, lead, mercury and manganese combined. The ores of these metals are concentrated in large, easily mined bodies, while titanium ores are dispersed throughout the earth’s crust.
Alloying with elements such as aluminum and vanadium can strengthen titanium. Titanium is nonmagnetic and possesses good heat-transfer properties. It has the ability to passivate, thereby giving it a corrosion resistance to acids. It is also nontoxic and biocompatible. These properties make titanium and its alloys useful in a wide range of structural, chemical, petrochemical, marine and biomaterial applications.
The most widely used titanium alloy, Ti-6Al-4V, is present in 45% of industrial titanium applications. The unique combination of this alloy’s physical and mechanical properties with workability, machinability, production experience and commercial availability make it economically useful. Some uses of this alloy are aircraft gas turbine disks and blades, airframe structural components and prosthetic devices. Ti-6Al-4V has become the standard alloy against which other alloys are compared in the process of selecting a titanium alloy for a specific application.
Valued in the petrochemical industry, titanium is used in heat exchangers and reactors. The automotive industry uses it in components including connecting rods, valves and suspension springs. The sporting-goods industry uses the metal in the manufacture of bicycles, golf clubs, tennis rackets and wheelchairs designed for the disabled who want to participate in a sport.
Titanium is used in condensers and turbine blades in electric power plants. It is also incorporated into the architecture of buildings, roofs, piping and cable. Because of its corrosion resistance, titanium and its alloys are used extensively in prosthetic devices such as artificial heart pumps, pacemaker cases, heart-valve parts and load-bearing bone or hip-joint replacements or bone splints. Human body fluids contain a variety of organic acids to which titanium is totally immune. Since titanium does not become magnetized, it is used in the structural parts surrounding computer components such as disk drives and microchips, which can be ruined by stray magnetism. Other common applications of titanium include shape-memory eyeglass frames, watches and jewelry.
Fig. 2. Applied Test Systems’ Universal Testing Machines are constructed from quality materials for longevity and engineered for precision. These UTMs offer testing flexibility and can easily be modified for a custom solution.
Researching, Testing and Verifying
Originating in Russia – home of the world’s largest producers of wrought-titanium product – was a specific need to test multiple dimensionally different titanium samples. Cost and space were an important factor, as with any business, constraining the number of universal testing machines (UTM). In addition to limited space, temperature control had to be within a tight specification and a precise level of documentation during the testing was imperative. It was necessary to make every attempt to eliminate human error and the constant monitoring and adjustment of the temperature controller. This assures the most accurate temperature uniformity possible.Based on the application, the force required to achieve the anticipated change in titanium material properties during an elevated-temperature test demanded a 33,720-pound (150.0 kN) UTM (Fig. 2). The furnace temperature requirement was 2200°F (1205°C).
The footprint and cost of this equipment limited the scope of this project to two UTM test frames. There was, however, a need to test six specimens per day, which posed yet another dilemma. As the time to heat each specimen was rather lengthy, due to the slow ramp-up of the temperature to prevent overshooting and reduction of the accuracy of the temperature control, testing six samples a day on two machines proved to be a challenge.
Fig. 3. WinTensile (Windows Elevated-Temperature Tensile) is data-acquisition software that provides extremely accurate temperature control. This custom software gives the operator the option to import and export raw data, “set and forget” temperature parameters and view data in charts and graphs.
Providing a Custom Solution
Determined to offer a solution, Applied Test Systems found that testing within the limitations would be permissible with the use of three furnaces per UTM. This required a unique load-train assembly, permitting two specimens to hang inside the furnace and preheat while another specimen was being tested. Due to the length of time to heat each specimen and the necessity to maintain constant, uninterrupted temperature control and uniformity, not moving the specimen more than a fraction of an inch when transferring the load trains posed a new problem.From a mechanical standpoint, this required the expertise of a creative engineering staff and teamwork between the manufacturer and the researchers in the test laboratory. A system was designed to allow three specimens to be simultaneously heated on a single UTM. While one sample was being tested, the other two specimens were in the heating process in the additional two furnaces. This was achieved by the use of a specialized load train with custom adapters to allow transfer of the load trains with minimal movement. Articulating furnace mounting arms attached to the columns of the UTM allowed each furnace to be moved in and out of the testing area, increasing uniformity control.
In addition to the unique mechanical design, furnace control and data acquisition required a custom solution. ATS needed to create a software program to provide extremely accurate temperature control and data acquisition. This software provided the ability to “set and forget” the temperature parameters. This unique, custom software would permit the user to set the temperature parameters once, with no need for readjustment (Fig. 3). This eliminated any potential errors during the control of the furnace and provided valuable, accurate data that can be analyzed and archived to confirm the accuracy of the tested material.
Teamwork for Tomorrow
Although the unique application was specific for testing titanium at an elevated temperature, the principles discussed can be applied to a wide variety of materials when measuring and analyzing materials characteristics. In the past, similar systems have been designed. This particular application, however, involved multiple changes to allow a custom solution. Since this system was designed, word quickly spread and several similar requests have been explored and quoted.It’s clear that to be a part of this growth in an ever-changing economy, you must be willing to provide custom solutions for new applications and employ the help of a talented and creative team. IH
For more information:Contact Applied Test Systems, Inc., 154 East Brook Lane, Butler, PA 16002; tel: 724-283-1212; fax: 724-283-6570; e-mail: sales@atspa.com; web: www.atspa.com
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