eXpert 1000 Series servo hydraulic testing machines are ideal for testing metals, composites, medical devices and implants, concrete, webbing, and other materials at very high load capacities without breaking your budget. Each frame employs strain gage load cells for direct measurement of force. No need to compensate for piston friction and other non-linearities, these frames offer exceptional accuracy and precision while reducing long-term calibration and service costs. A simple design based upon off-the-shelf components allows for lower cost, faster delivery, continuous testing to maximum load, and years of maintenance free operation. The hydraulic power supply and electronics are integral with the frame thereby saving valuable lab space.
eXpert 1600 Series frames are capable of performing static tension, compression, and bend tests. eXpert 1900 Series dynamic fatigue testers are engineered to meet the force-stroke-frequency requirements of your application. ADMET offers a full line of grips, fixtures, load cells, extensometers and heating and cooling systems. All ADMET machines can be modified to satisfy special stroke, load, and fixturing requirements.
ASTM A370 is performed by steel manufacturers and commercial and government laboratories serving the construction industry to measure the strength of rebar. Values of ultimate tensile strength, yield and elongation are required for the most common sizes.
Why is it done?
Steel manufacturers are required to test the products they sell to ensure that the specifiction cited is met. Significant liabilities can result from providing noncompliant product. Tensile testing to failure is the most common method employed. These often include the use of extensometers for the measurement of Yield.
In the United States, the size designations of these mild steel bars used to reinforce concrete are set by ASTM International. Rebar is generally supplied in 20- and 60-foot lengths.
Most bars are “deformed,” that is, a pattern is rolled onto them which helps the concrete get a grip on the bar. The exact patterns are not specified, but the spacing, number and height of the bumps are. ASTM A615 defines these markings.
Typical deformed reinforcing bar (courtesy of Concrete Reinforcing Steel Institute)
Three grades are defined:
Minimum Yield Strength
per Square Inch
The size designations up through size 8 are the number of eighths of an inch in the diameter of a plain round bar having the same weight per foot as the deformed bar. So, for example, a number 5 bar would have the same mass per foot as a plain bar 5/8 inch in diameter.
Users of rebar are required to test the rebar they receive using independent sources prior to acceptance. There have been issues with substitution of grades and materials not meeting the intended specification. Testing helps to minimize the possible installation of out of spec rebar.
Why is it important?
The strength of rebar is a fundamental requirement in the design and construction of buildings, dams, bridges, roads and airports. The failure of a single rebar may result in significant loss of strength in the structure under construction with the possibility of catastrophic failure.
Rebar installation (courtesy HDR Engineering)
What ADMET equipment is needed?
Many steel manufacturers and independent testing laboratories own tensile testing machines of considerable force capacity. These older machines constitute a considerable investment so automating an existing system via upgrade/retrofit is a prudent decision. The upgrade/retrofit is performed at the customer’s site including training.
Rebar fixtures including holders and long gauge length extensometer are among the tools ADMET offers for the testing of rebar.
Changes in the force rate being applied to the rebar can affect the yield strength, tensile strength and elongation values which are highly strain rate sensitive. In general the yield strength and tensile strength will increase with increasing strain rate. Elongation values generally decrease as the strain rate increases.
Rebar testing using manually operated machines places a burden on the technician performing the test. The rate of testing is deliberately slow and thus the length of time to test can be long. All the while the operator is expected to be monitoring and adjusting the controls of the machine to ensure there is consistent force application at the specified rate. This is often not the case and inconsistent force application from test to test is the inadvertent result. Undesirable scatter in the test data can occur and sometimes good product gets rejected while at other times out of spec product can be deemed acceptable. Automatic control minimizes this scatter and provides inherent documentation of the testing force application.
40ksilbf neededto test yield
60ksilbf neededto test yield
75ksilbf neededto test yield
Table 1. Rebar size versus yield strength in pounds force for 3 grades
Note: Not all sizes are available in all strengths. Ultimate tensile strength is typically between 1.33 (larger sizes) to 1.75 (smaller sizes) the yield strength.
Do I retrofit or replace my hydraulic universal testing machine?
What do you do when your outdated hydraulic materials testing machine breaks or your customer requires a test that cannot be performed with your existing system? Do you replace the testing system with a new one or do you upgrade/retrofit with new software and controls?
There are two hydraulic universal testing machine designs. The first uses a single sided ram to apply force and requires gravity for the piston to return home. This type of hydraulic testing machine is the most common and is used for static tests only. A schematic of a ram based hydraulic tester is shown in Figure 1. The second type of hydraulic machine uses a dual acting piston. The dual acting piston design provides control in both the up and down direction and is commonly used for fatigue testing applications.
Figure 1 — Schematic of a single acting ram based hydraulic universal testing machine
Comparing the purchase of a new machine or an upgrade to an existing hydraulic testing machine, it is almost always less expensive to upgrade the existing machine regardless of force capacity. New ram based static 20,000 lb and 400,000 lb hydraulic testing machines cost between $35,000 and $200,000, respectively. In general, retrofits cost between $500 for the integration of a simple digital indicator to $30,000 for a new servo-hydraulic power unit with a PC/Windows-based materials testing system. As a rule, the amount of money you save retrofitting a hydraulic tester increases as the capacity of the machine increases. So, a retrofit would save well over $100,000 on a large machine and thousands of dollars on a smaller machine.
In addition to the direct machine costs, there are other considerations that come into play, such as your investments in grips, fixtures, and test jigs. The larger the investment, the greater the replacement expense. If all of your testing systems are similar, then it is best from a fixturing, training and maintenance standpoint to retrofit the testing machines. Finally, there is the very pressing situation of when your existing machine has failed. A retrofit can be installed much more quickly than it would take to purchase a new machine.
Hydraulic testing machines are generally used to test metals and metal components at higher forces. Their ability to perform millions of static tests and fatigue cycles with little mechanical wear makes the hydraulic testing machine well suited for these testing applications. Because of their durability, the hydraulic testing machine is an ideal candidate for retrofitting.
Types of Hydraulic Retrofit Packages
A number of upgrade packages are available for retrofitting hydraulic testing machines. In general, the upgrade packages, once installed and calibrated, will extend the ASTM E4 certified force measuring range of the machine. A description of possible upgrade package types for manually operated hydraulic testing machines follows:
Basic Upgrade: The simplest upgrade keeps the existing manual control valves and replaces the dial gage or existing digital indicator with a new single channel digital indicator to display load and report ultimate tensile strength. Some of the more sophisticated single channel indicators are also capable of calculating yield by the halt of the pointer method and downloading results and load vs time data to a computer for reporting and plotting.
Figure 2 — ADMET Gauge Buster 2 Digital Indicator. Displays live load, peak load, load rate and ultimate tensile strength. Results and XY data can be uploaded to computer to generate reports and plots
Three Channel Upgrade: The next step up when keeping the existing manual control valves is to incorporate a two- or three-channel digital indicator that is capable of measuring force, displacement, and strain. A testing machine equipped with a two or three channel indicator is capable of generating a stress-strain curve and calculating offset yield, Young’s modulus, ultimate tensile strength, and percent elongation according to ASTM E8 Standard Test Method for Tension Testing of Metallic Materials. Results and stress-strain curves can be uploaded to a computer for further review and analysis. New or existing extensometers can be connected to the indicator for measuring strain.
Figure 3 — ADMET’s eP2 Digital Controller can be installed on both manually operated and servo controlled testing machines. The eP2 features a load and position input plus an optional strain channel. Results and XY data can be uploaded to a computer running the GaugeSafe Data Exchange Program to perform analysis according to ASTM E8 and generate stress vs. strain curves and test reports
PC/Windows Based Upgrade: Installing a PC/Windows based materials testing system is the most sophisticated upgrade package for a manually controlled hydraulic testing machine. It provides all of the capability of the three channel digital indicator but adds calculations for plastic strain ratio (ASTM E517), K and n values (ASTM E646), plus many more. PC based materials testing systems also provide more data handling and reporting capabilities than a standalone digital indicator.
Figure 4 — A 400,000 lb capacity manually operated Tinius Olsen Testing Machine retrofitted with ADMET’s MTESTQuattro® Materials Testing System. MTESTQuattro features load, position, axial strain, transverse strain and auxillary input channels
The next level of retrofits convert manually operated machines to automatic closed-loop servo hydraulic testing systems that are microprocessor controlled. This is accomplished in one of two ways.
Basic Servo Retrofit: The least expensive servo retrofit option is to keep the existing hydraulic power unit, bypass the existing manual control valves and install a new servovalve manifold. Either a multi-channel digital indicator or a PC/Windows based materials testing system can be used to control the machine. The standalone digital indicator is more suitable for running similar tests repeatedly, whereas the Windows based system provides more control capability for performing a variety of tests.
Full Servo Retrofit: The more expensive servo retrofit is to replace the existing hydraulic console with a new servo hydraulic power unit (see Figure 5). Again, either the multi-channel digital indicator or Windows PC-based system can be used to perform the tests.
Figure 5 — A 60,000 lb capacity Baldwin Universal Testing Machine retrofitted with a new servo-hydraulic console equipped with ADMET’s MTESTQuattro® Materials Testing System. The servo based system ensures that tests are performed automatically according to ASTM specifications
In addition to upgrading existing manually operated testing machines to servo control, it is also possible and quite common to upgrade the controller and software on an existing servo equipped static and fatigue rated hydraulic testing machine. This an economical solution because the new controller and software only has to be attached to the existing load frame and hydraulic power unit.
Regardless of whether you retrofit or replace, it is important that you keep your testing capabilities current. Up-to-date equipment will reduce test times, eliminate data entry errors, and speed materials and product development. Employing testing systems that automatically perform the tests according to specification, automatically calculate results and seamlessly communicate with computers and programs running on your corporate network are paramount to operating a successful testing laboratory.
ASTM F2634 Polyethylene Butt Fusion Joint Test Testing Equipment
Test method ASTM F2634 is used to determine the quality of polyethylene (PE) butt fusion joints. This test is desinged for pipes with a diameter greater than 2.37″ and a wall thickness greater than 0.25″.
In this test a PE “dogbone” shaped specimen is pulled in tension at a rate of 4-6 inches per second. The specimen has holes on each end which allows them to be pinned to the upper and lower crosshead. The speed of this test is quite fast and the fixturing provides clearance to allow the machine to quickly gain enough speed before the impact takes place. After the test, the following are typically reported:
Average Rate of Speed
Recorded force / vs time chart
Type of rupture
Testing machine with a controlled rate of crosshead movement (constant rate of extension)
Speed of 6 inches per second (360 inches per minute)
Data aquizittion rate of 1000 HZ (1000 samples per second)
Fixturing to provide impact clearance and hold samples
Position indicator (LVDT, encoder, extensomer, etc.
McElroy, a company that designs and manufactures a complete line of fusion equipment, makes a machine specifically for this test called the McSnapper. It looks nice but we don’t know anything about it.
At ADMET we studied ASTM F2623 and determined that our ExPress line of hydraulic universal testing machines offer the best solution for this test. A standard ExPress system with a modified pumping system to increase the maximum speed would satisfy all requirements of the specification.
This is our recommended system:
Express hydraulic universal testing machine. For example, the Express 50kN would have the following specifications:
Capacity: 50kN (11,250 LB)
Power Stroke: 4 inches (Other Stroke Lengths Are Optional)
BarronCast Uses ADMET System to Bring Mechanical Testing In-House
BarronCast Inc. (BCI) provides investment castings and machined parts in a competitive environment to demanding customers in defense, automotive, medical and other industries. It is ISO/TS 16949 and ISO 14001 certified. It produces cast iron, carbon, stainless and tool steels, aluminum and copper alloys.
Quality control is a critical part of its production process for all customer industry sectors. BCI recently moved most of its quality testing in-house in order to reduce turnaround time and manage the process. Commented Greg Barron, BCI Manager of Engineering and Quality Assurance, “We found that we can do the testing, certify and ship ourselves – we didn’t have to wait for outside test results.”
One of the tests that BCI is now conducting in-house is tensile testing. Barron’s original thought was that a used, retrofitted machine would be the most cost effective path. Barron checked into new and retrofitted Instron, Tinius Olsen and other manufacturers’ test frames. He noticed that ADMET controllers and indicators were often used in the retrofits. He contacted ADMET and discovered that, for the price of a retrofitted machine, about $25,000, he could buy a new machine.
After discussing his needs with ADMET to make sure that its machine could handle testing BCI’s highest tensile strength material, hardened 17-4-PH Martinsitic Stainless with ultimate tensile psi strengths of over 200,000, he ordered an ADMET ExPress servo-hydraulic, dual column test frame equipped with the MTESTQuattro materials testing system for use in both R&D and production testing.
Said Barron, “We see a lot of possibilities. Part of the investment casting process is to build a ceramic shell. Periodically, we send them out for a four-point bend test. With the proper fixturing we could use the ExPress to test our ceramic shells in-house.
Niacc-Avitech Technologies Uses ADMET ExPress for Aircraft Shock Absorber Servicing
Niacc-Avitech Technologies is an aircraft component overhaul and manufacturing facility in Fresno, CA. A subsidiary of HEICO Aerospace, the company repairs and overhauls starter/generators, fuel assemblies, cable harnesses and electronics, brake and hydraulic components, and other aircraft appliances and components.
Niacc recently received a customer request to add overhaul capabilities for landing gear shock absorbers to its portfolio of services. The technical specifications required load vs. position and cyclic properties certification of shock absorbers according to OEM specifications that would require new test equipment.
“The load issue was one of the real challenges,” Explained Rayan Kabeer, Niacc head of Engineering and Product Development. “For this type of shock absorber we were looking into 49,000 pounds. Everything other companies had was too big or too small. They could have custom made it, but it would have taken a tremendous amount of time.”
“We talked with ADMET about load and pressure and what the requirements were,” he said. “We gave them all the parameters that we needed and there was a lot of back and forth. They pretty much said, â€˜we can do it.’”
ADMET specified an ExPress 300 kN (60,000 lbf) dual-column servo-hydraulic materials testing machine with a top mounted actuator (as specified in the CMM). ADMET also recommended the MTESTQuattro Materials Testing System, a Windows-based software controller with advanced analysis and reporting capabilities.
The unit arrived within six weeks. “We just had to hook [the machine] up with our computer and then load the software. We installed the load cell ourselves and it was pretty much plug and play,” Kabeer said. “The best thing about ADMET is that, with their software, we can control [the test] pretty much hands-off.”
Niacc-Avitech Technologies Uses ADMET ExPress for Aircraft Shock Absorber Servicing
Researchers at the University of Connecticut, in cooperation with the Connecticut Department of Transportation, tested and developed a low-cost passive wireless crack sensor using commercial RFID tags (single tag and multi-tag) for crack detection of field metal structures.
Tensile testing was completed with an ADMET eXpert 1655 Hydraulic Universal Test System with 250kN load cell. The tensile grips were clamped flush with the interior edge of the anti-buckling plates. The test setup included a digital image correlation (DIC) system to observe the crack propagation area. Pre-cracks were formed by applying a tensile load at low strain rate, typically 0.0025 in/min until a maximum load was reached followed by a visible crack extending from the machined notch, approximately 0.0875 inches for small samples and 0.1875 inches for large samples. The sample was monitored at roughly 10x magnification during this operation and crack length was measured to 0.05-mm precision. To enable communication between the RFID tags and the reader antenna, a substrate material between the tag and the metal surface was found.
The first major experimental study was on the crack detection capability and sensitivity to damage of both sensor configurations: single-tag and multiple-tag and the damage sensitivity of multiple sensors were studied for crack detection. The results showed that the developed sensors have great potential to effectively detect the existence, location, and the degree of cracks. Therefore, the complete damage sensitivity of the RFID-based crack sensors were successfully validated.