Fracture three-point bending specimen

The third example of time effects in elastic fracture concerns accelerated crack growth. Up to the early 80 s it has been assumed that a unique relation exists between the stress intensity factor K and the rate of crack growth da/dt. This contention had been confirmed in many steady crack growth experiments. Using three point bending specimens Chan and Williams [33] obtained for HDPE in water the following relation between da/dt, and the acting stress intensity factor Kc ... 

Manhanty D.K., Savent G.Y. 1992. Experimental investigations on stable crack growth in three-point bend specimens under mode I and mixed mode (I and II) loading[J. Engineering Fracture Mechanics, (43) 41-53. 

The DT test [ ] is similar in concept to the CVN test. The simplicity of a three-point bend specimen has been combined with an energy criterion for fracture resistance. In this test, a 16 mmx38 mmx 181 mm specimen with a sharp notch is fractured on a large pendulum or drop-weight impact machine, and the fracture energy is measured. 

The figure also shows a schematic diagram of load vs displacement plots describing the procedure for determination of the critical load in a linear-elastic fracture mechanics (LEFM) test (see Fig. 10.1c). The determination of Ki is dependent on testing the material under conditions in which it exhibits essentially linear-elastic behavior indicative of a plastic zone that is very small relative to flaw size and specimen dimensions, the domain of LEFM. The equations for the compact specimen and three-point bend specimen are as follows ... 

The two most common specimen types used to measure fracture toughness are (a) the three-point bend specimen shown schematically, and (b) the compact specimen shown mounted in grips with a clip gage extensometer attached. Panel (c) shows a schematic diagram of various types of load vs displacement plots describing the determination of an LEFM test (ASTM, 2013c). 

Mode 1 Fracture toughness from notched three point bending specimens... 

Fig. 6. Fracture toughness test specimens (a) single-edge notch (b) center notch (c) compact tension and (d) three-point bend. Terms are defined in text.

Pig. 1 a and b. Fracture toughness test specimens a three-point bend and b compact tension. Pre-crack length denoted by a. Movement of crosshead is vertical for both... 

Fracture toughness for siloxane-modified as well as ATBN- and CTBN-modified resins was monitored through KIC, plane-strain fracture toughness 44). The Klc values of at least five three-point bend (3PB) specimens of each material were calculated according to Eq. (1)... 

Fig. 9 Specimen geometries for fracture measurements a compact-tension, b three-point bending...

Block polymer B differs substantially in its failure characteristics from BP A polycarbonate. For the block polymer a mixed failure mode predominates in three-point bend tests of notched specimens from —100°-90°C. In the mixed mode craze breakdown and plane strain fracture occur first inside the specimen subsequently shear failure occurs in the surface regions of the specimen. Shear lips (11) are formed as a result. Shear lips are also found on the notched Izod impact fracture surfaces of block polymer B, implying that the same mixed mode of failure occurs under high speed loading conditions. 

A rectangular bar of polymer of thickness B = S mm and width = 20 mm has a central notch of length a = 10 mm. The bar is loaded in a three-point bending test with an 80 mm span, S, at room temperature. The bar fractures when the force applied is 300 N. Calculate (a) Kjc for the polymer and (b) the force needed to fracture in a compact tension test a specimen of dimensions IT = 50 mm, J = 10 mm, having a single-edge sharp crack of = 25 mm. 

Fracture tests on notched bulk adhesive specimen have been made in three point bending to observe the real mechanical behaviour of the resin [16]. The Young s modulus is estimated to be equal to 96 10 MPa and fracture energy measured reaches 3900 600 J/m and the PU resin displayed softening behaviour. 

The stress-strain curves of Zr02-Ni system in three-point bending test are presented in Figure 2. It can be found that the Zr02-Ni system shows quite different deformation and fracture behavior with the change of constitution. The nickel-rich material displays typically elasto-plastic deformation behavior, which is controlled by the continuous matrix nickel phase and similar to metallic material. During bending test, the specimen can be bowed to V shape... 

The single edge specimens were loaded under three-point bending at cyclic frequency of 10 Hz, stress ratio of 0.1. The FCGR tests were carried out in the laboratory air at the temperature of 20 °C and 700 °C. Several control tests of the composites were performed at the temperature of 800 °C. Optical and scanning electronic microscopy was used for analysis of microstructure and fracture micromechanisms of the materials. 

Adolf et al [27] developed a physically realistic continuum-scale constitutive equation-based theory which they implemented in a finite element scheme. An especially interesting recent publication from this team [175] investigates cohesive failure in partially cured epoxies. KIc was measured with notched three-point bend fracture specimens at a constant (T-Tg) value (thereby normalizing the viscoelastic relaxations) and was shown to manifest a strong dependence on the crosslink density. It increased by more than an order of... 

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