Supporting Materials Mechanics Research of Variable Frequency and Amplitude
By Dr. Jian Fang from Baowu Group
Long-term mechanical properties of materials under variable frequencies and amplitude will be a trend in the future. For a traditional servo-hydraulic machine, its frequency range is too small, the maintenance costs are high and also there is a lot of noise whilst a test is running. And also if we want to do the fatigue test of ultra-thin steels, the traditional electromagnetic resonance of high-frequency fatigue testing machines are found to be difficult to control. Both challenges urge us to find new solutions.
The Chief Engineer of Mechanical Testing of the Central Research Institute from Baowu Group, Dr. Jian Fang
Following the mergers of China South Railway and China North Railway, China COSCO Holdings Company and China Shipping (Group) Company, Baosteel and WISCO which are the leaders of the steel industry in China were merged in September 2016, becoming the largest Baowu Iron & Steel Group in China. The successfully-merged Baowu Group will keep following their 3 transformation strategies - "the transformation from steel to materials" - developing new materials based on the steel industry; "from manufacturing to service" - be involved in modern trade logistics industry, industrial services, urban services, industry and financial industry; and finally to grow "from the leader in China to the leader in the world's steel industry and to become a world-class enterprise group".
To comply with the three strategies, the Mechanics Laboratory of the Central Research Institute (Technical Center) has made tentative attempts in the field of industrial materials, especially in new energy materials based on the mechanical properties evaluation and test methods development of raw steel materials.
As we all know, research and development of materials and applications should keep up with the times. When you step on the accelerator, the driving mechanism will speed up from acceleration to stable running rate, and then brake and decelerate. This cyclic running exposes materials to loading frequency from high to low then to a constant rate. One typical application is the steel used in the electrical machinery of new energy vehicles. Therefore, traditional fatigue tests of constant amplitude and frequency have been unable to meet the technical problems faced by the new materials such as newer energy vehicles. Changes in environment, speed, amplitude, and frequency have become the main topics of new energy automotive materials.
"Long-term mechanical performance studies of materials under variable frequency and amplitude will be the future trend," Dr. Fang said. However, in China, we still follow the test standard GBT 15248-2008. Low cycle fatigue test of metal materials under axial constant amplitude obviously can't meet the test requirements of above materials. There's already international standard ISO 12110-1-2013: Metallic materials -- Fatigue testing -- Variable amplitude fatigue testing -- Part 1: General principles, test method and reporting requirements for testing this kind of material; but a relevant Chinese standard is still not released. With the rise of new energy vehicles and the promotion of Chinese government, many well-known vehicle manufacturers such as Tesla, Volkswagen, and General Motors have already established their own materials fatigue test standards. The new concepts such as variable amplitude, variable frequency, and variable temperature test undoubtedly put forward new requirements to global material suppliers. For many materials suppliers including Baowu steel, finding corresponding test solutions as soon as possible has become a new topic and a new challenge.
Since it is an emerging challenge, it is crucial to break through the traditional test methods and to find efficient solutions. As the chief technician, Dr. Fang has extensive experience in testing metal materials. In his opinion, there are many ways to do fatigue tests, but few devices can measure accurately under variable amplitude, frequency, and temperature.
Electro-hydraulic servo fatigue testing machines are usually selected when doing materials fatigue test under variable amplitude, frequency, and temperature, but its frequency capacity is only a few dozen hertz, which is unable to meet the needs of high-frequency testing and also has low test efficiency. Although electromagnetic resonance high-frequency fatigue testing machines can do high-frequency testing, they don’t have the ability to test under variable frequency amplitude. This is especially difficult whilst testing lightweight materials.
“On the one hand, the efficiency of traditional electro-hydraulic servo fatigue machine is low as the hydraulic pump station costs so much in maintenance and makes a lot of noise. On the other hand, traditional electromagnetic resonance high-frequency fatigue testing machines are found difficult to control when conducting fatigue tests on some ultra-thin consumer grade steels. These challenges urge us to find new solutions to fatigue tests," Dr. Fang explained to us.
Dynamic and static electronic fatigue testing machine cost little in maintenance and can do the test under variable amplitude and frequency, which combines the advantages of the high-frequency function of high-frequency electromagnetic resonance machine and the ability to program variable amplitude and frequency of low cycle fatigue testing machine. It's very suitable for mechanical testing of ultra-thin and lightweight materials. More importantly, it occupies a very small area and is easy to maintain, with no need of cooling water and hydraulic oil. Finally, it only needs one single-phase power supply in the laboratory and with little power consumption. Dr. Fang was immediately attracted by the well-designed and versatile dynamic and static electronic testing machine from Instron at one exhibition.
For traditional fatigue tests, we often choose frequencies as high as possible, hoping to hit the fatigue limit in a short period. However, the fatigue test of new material has changed. We are curious as to what will happen to the fatigue properties of steel either under variable amplitude or variable frequency.
All these kinds of test can be done using Instron E10000, and the test results have been initially recognized by customers. In addition to metallic materials, we also use E10000 to test food-grade lightweight materials and plastics. In summary, from low-speed static test to high-frequency closed-loop dynamic test, ElectroPuls static and dynamic testing machine can fulfill all your test requirements!
More than that, Dr. Fang also emphasized that another significant advantage of Instron is that all its accessories can be shared. Its load cells, fixtures, and extensometers can be configured by the same series of instruments, which saves time and cost for customers. "Such as Instron AVE, it can be used on from 1-ton static machine to 25 tons dynamic machine in our lab," Dr. Fang said.
Although the Instron E10000 machine was installed and used in less than one year, the technicians of Baowu have accumulated much experience in the field of variable amplitude and frequency fatigue testing based on this testing machine. We believe that with the development and promotion of the new energy industry, Instron ElectroPuls static and dynamic testing machines will have a much more versatile application area.