J-Integral Fracture Toughness Test Equipment J1C

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J-Integral Fracture Toughness Test Equipment J1C

Humans have found widespread use for metal materials since pre-Bronze Age times when we began to smelt metal ores, forming hard and resilient tools. Although the ductility of metals, their ability to plastically deform, is a well known and exploited property, failure of metal parts often occurs as a brittle fracture. Fracture toughness tests measure the ability of a material, containing a flaw such as a crack, to resist further crack growth and propagation to failure. The fracture toughness of a material is actually a measure of the energy absorbed by the material up to fracture. Metal components used in the construction of aircraft, bridges, and buildings will undergo both high and low cycle fatigue, which can cause the initiation of fatigue cracking. Structural engineers use fracture toughness test data to determine the load capacity of structural components after crack initiation and throughout crack growth. This allows the establishment of component lifespans, along with inspection and maintenance criteria. When validation requirements cannot be met for linear-elastic fracture toughness (KIc), or when the crack tip plastic zone is not small compared to crack size, testing and analysis must be conducted for the J-integral elastic-plastic fracture toughness (JIc).

A typical fracture test procedure precracks the metal test specimen using cyclic fatigue loading in the range of 10,000 to 100,000 cycles at frequencies up to 100 Hz. This precracking provides the best simulation of a natural crack. The precracked metal specimen is subjected to slow-rate load/unload cycles, measuring load vs. crack extension. This data is used to calculate the J-integral for each load/unload cycle, forming a series of data points plotted against crack extension. This J-integral crack resistance curve, J-R curve, is the primary analysis tool to determine an interim J-integral fracture toughness that is evaluated against acceptance criteria for J1c validity. The calculations involved in validation and processing of J-integral fracture toughness test data involves a number of tedious calculations. TestResources offers a range of control, data acquisition, and processing software that performs on-line data collection, providing real-time J-integral vs. crack extension and load vs. displacement plots, and off-line post processing to calculate the required validation parameters and test results. The software removes the hassle of calculating test results and compiling test reports, allowing quicker and easier verification of proper test procedures and specimen geometries. ASTM has developed extensive test methods for testing the fracture toughness of various materials, exhibiting elastic-plastic crack growth behavior. ASTM E1820 is the general standard for fracture toughness containing test procedure and analysis methods for both elastic-plastic, J1c, and linear-elastic, K1c, behavior. ASTM D6068 is the standard method for J-integral fracture toughness of plastic materials.

TestResources recommends the use of servo-hydraulic or electro dynamic machines for fracture toughness testing. These machines can be used for every stage of fracture toughness tests, capable of the high frequencies needed for specimen fatigue precracking and the high forces needed for fracture toughness measurement. Clevis grips are used for fracture testing of compact tension C(T), disc shaped compact tension DC(T), and arc shaped tension A(T) specimens, while side edge bend SE(B) and arc shaped bend A(B) specimens are tested using special bend fixtures that have rollers capable of rotation and slight translation.