Testing of Heavy Plates

They are used primarily in the construction industry, for large bridges, in large-scale construction and shipbuilding, for offshore drilling platforms and in wind turbines, and for heavy equipment such as cranes and excavators. Furthermore, they are used as semi-finished products for large pipes that transport oil and gas over long distances.
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In many applications, compliance with characteristic values or specification limits for safety in long-term use is required. The relevant and required characteristic values are determined depending on how the heavy plate is used. The test methods used for this segment are methods often used in heavy plate testing. In special applications or uses, other test methods not mentioned here can be used to ensure safe and long-term use and operation.

Heavy plates are steel sheets with a width of up to four meters and a thickness of at least three millimeters up to approx. 250 mm and a length of up to twenty meters. They are manufactured by the reverse thermomechanical rolling of slabs. 

Tensile Tests

Tensile tests on heavy plates are mainly performed according to ISO 6892-1 and ASTM E8, which are internationally recognized and widespread standards. ISO 6892-1 is also a European standard (EN ISO 6892-1) that is identically worded, and thus applicable in the European Union (DIN EN ISO 6892-1 in Germany). Tensile specimens for this type of tensile test are removed from heavy plate in such a way that the sheet thickness is retained as specimen thickness to the greatest degree possible. Specimens have a correspondingly large cross-section and usually require materials testing machines with a high load range or heavy load range. The parallel length or the part of the specimen deformed under load is produced by milling. The unprocessed thickness and the careful milling and smoothing of the specimen thickness ensure that the specimen is changed only slightly and therefore material characteristics are hardly influenced. 

Wide range of testing solutions

Zwick offers a wide range of standard and customized testing systems up to 2500 kN. These testing systems can determine material characteristics according to the standard with a high level of accuracy. Zwick's parallel closing, hydraulic specimen grips ensure that perfect clamping and positioning of specimens are maintained throughout the entire test, preventing the specimen from slipping or sliding. 

Standard-compliant strain measurement.

In most cases, standard-compliant strain measurement is performed by automatic contact or optical (non-contact) extensometers. Zwick's makroXtens is the classic and tested solution for the testing of heavy plates. Thanks to its mechanical construction featuring high resolution, and a very high level of accuracy and robustness, makroXtens withstands harsh environments. It's robust mechanical construction enables continuous strain measurement up to specimen break. Automated determination of strain at break is possible without onerous markings and manual measuring after specimen remains are sorted. 

Strain measurement up to break

laserXtens is an innovative solution for strain measurement up to specimen break, fulfilling standard requirements (ISO 6892-1, ASTM E8, ISO 9513, and ASTM E83) for heavy plate specimens with flying colors. laserXtens does not require specimen markings; using a laser light, it uses the pattern it creates itself as markings on the surface. The optical evaluation of this "self-marking" is done so that even cinders and the occasional spalling of cinder does not disturb the markings. 
Since 2009, ISO 6892-1 and ASTM E8 allow the test speed to be automatically controlled and regulated by the strain rate. The tolerances called for in the standards for strain rate control (in particular those relevant to closed-loop strain rate control) can be easily met by both the makroXtens and laserXtens extensometers. 

Hardness Testing

Hardness tests on heavy plates are performed in a variety of ways. Depending on the application, hardness tests are performed to ISO 6506-1, (Brinell), ISO 6507-1 (Vickers), ISO 6508-1 (Rockwell), ASTM E10 (Brinell), ASTM E384 (Vickers and Knoop), and ASTM E18 (Rockwell). Other methods or regulations are also used in certain application areas (for example, the European standard EN 2002-7 for applications in aerospace); for the testing of large surfaces and non-destructive testing, QEM methods are used (for example, the 3MA method), which is described in the VDI Guideline VDI/VDE 2616-1 (Hardness Testing of Metallic Materials). 

Testing and determining the average global hardness value 

One aspect of hardness testing is the testing and determination of the average global hardness value of sheet after rolling. Rolling is a thermo-mechanical process used to determine sheet thickness, as well as mechanical properties. Hardness methods that employ higher forces are used to determine the average values of these sometimes coarse structures. Preferable methods are Brinell or Rockwell. In the testing of heavy plates, portable hardness testers are also often used. They can be used on site on the original part. Coupons are taken from heavy plates when stationary hardness testers are used. They are used as the specimens themselves, or smaller specimens are taken from the coupons and prepared for a hardness test. 

Determining the grain structure of metallographic constituents with hardness tests

Another aspect of hardness testing is the determination of the grain structure by performing hardness tests on metallographic constituents. Due to the small size of metallographic constituents, hardness testers with small to very small forces are used—generally speaking, stationary microhardness testers with indention sizes and depths that can be adjusted via the indention force to the dimensions of the metallographic constituents. 
The Zwick product portfolio offers hardness testers and devices for all test methods. Zwick hardness testers and devices meet the requirements of all common international standards and can also be calibrated to international standards. As a calibration lab, Zwick is accredited for the calibration of hardness testers by the German national accreditation body, DAkkS.

Charpy Impact Test

Notched impact strength is an important characteristic for applications in pipeline construction and shipbuilding and can be determined with Charpy specimens in pendulum impact testers. The test method is described and defined in the international standard ISO 148-1 and in ASTM E23. The ISO standard is identical to the European standard EN ISO 148-1. In a Charpy impact test, the standardized notched specimens are inserted by hand, by means of simple feed devices, or using robotic systems and impacted at up to 750 J. The tests are performed at ambient temperature, but also at low temperatures to determine the high to low transition temperature. Zwick supplies temperature conditioning baths for correct conditioning of specimens down to –70°C and temperature conditioning devices for down to -180°C. Under the Machinery Directive, pendulum impact tester operation is subject to strict safety requirements, which are comfortably met by Zwick’s safety housing and sophisticated safety technology.

Fracture Toughness Testing

Fracture toughness testing KIc is an important characteristic for metal materials in safety-related applications such as aircraft construction, power plant construction, and even automotive engineering. Fracture toughness is determined using a specimen in which an artificial crack has been introduced. The crack is introduced usually through notching of the specimen followed by pre-cracking until a defined crack length is achieved. The specimen is then loaded quasi-statically to break. Fracture toughness can be determined from the load-deformation curve and the length of the crack. Details of the test procedure are contained in the relevant standard (ASTM E 399). Other relevant standards are ASTM E813, E1152 and E1290.

 Two-stage test for KIc determination

The two-stage test for KIc determination can be performed efficiently on Zwick Vibrophores and then on Zwick materials testing machines. Crack formation in the specimen is instigated by the mechanically produced notch followed by cyclic loading. The Vibrophore's high frequency allows rapid generation of a defined crack (pre-cracking). The process is highly reproducible thanks to the high sensitivity of the resonant frequency to crack formation.

Compact specimen (CT specimen)

The specimen geometry most frequently used is the specimen referred to as a CT (compact tension) specimen. The load is applied through pins inserted into holes in the specimen, yielding a mixed tensile and flexure loading.

SENB specimens

In addition to CT specimens, single-edge notched bending (SENB) specimens are used. While the testing method is simpler for the flexure specimen than the CT specimen, the required specimen volume is significantly greater. This is shown clearly in the illustrations.

Robotic Testing Systems

Safe, precise, reliable handling of heavy specimens places severe demands on operators of tensile tests. Zwick's automated robotic testing system solutions help to satisfy these requirements, by relieving the load on the operator, minimizing operator influence, and increasing operational safety and reliability. Under Zwick’s automation concept, specimens awaiting testing are manually sorted into magazines. From this point (storing the specimen). the tensile test is performed automatically, right up to sorting the specimen remains for inspection if required. Depending on requirements, additional measuring devices and test devices can be integrated into this fully automated sequence in addition to the tensile testing machine, particularly Zwick’s cross-section measuring device with four independent, automatically applied measuring transducers for precise and standard-compliant determination of cross-sectional area.
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