Four-point-bend method

EXPERIMENTAL ANALYSIS OF GLASSY POLYMERS FRACTURE USING A DOUBLE NOTCH FOUR POINT-BENDING METHOD... 

Measurement of the elastic moduli such as E is made using rods of either circular or rectangular cross section and (generally) three or four point bending methods. The manner of putting the load on the sample is shown in Figure 10.02. 

Three- and four-point bending methods have been used to evaluate interfacial fracture energy quantitatively and to characterize the interfacial fracture between dissimilar... 

The four-point bending method requires a simple bend bar of the coated substrate with a notch machined in the coated layer (Fig. 6.1). The four-point bend delamination... 

Flexural strength is determined using beam-shaped specimens that are supported longways between two rollers. The load is then applied by either one or two rollers. These variants are called the three-point bend test and the four-point bend test, respectively. The stresses set up in the beam are complex and include compressive, shear and tensile forces. However, at the convex surface of the beam, where maximum tension exists, the material is in a state of pure tension (Berenbaum Brodie, 1959). The disadvantage of the method appears to be one of sensitivity to the condition of the surface, which is not surprising since the maximum tensile forces occur in the convex surface layer. 

ASTM D 6272, Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending ... 

In this work, DC electric field-assisted ion exchange was carried out to enhance the sodium-potassium inter-diffusion and improve the mechanical performance of borosilicafe glass. Elecfric fields with intensity varying between 100 V cm and 3000 V cm were applied in both direct and inverted polarizations. Four point bending test and the Vickers indentation method were used to characterize the mechanical properties. Energy dispersion x-ray spectroscopy was carried out to determine the potassium concentration within the surface layers of the samples. 

A commercially available polycrystalline alumina is tested using three different methods three-point bend, four-point bend, and uniaxial tension. The resulting MOR values are 550, 410, and 175 MPa, respectively. What conclusions can you make about the material from these data ... 

Modulus of rupture, MOR. was obtained on polished samples by four point bend tests (4 X 20 mm) with 1 mmmin deformation rate using Instron equipment. The elastic modulus, E, was measured at room temperature, by the acoustic resonance method using a self-assembled apparatus and, at high temperature, from the stress-strain curve obtained in the four point bend tests. 

This test method determines the asphalt s behaviour under repetitive fatigue loading in a four-point bending test equipment in which the inner and outer clamps are symmetrically placed and a slender rectangular-shaped specimen (prismatic beam) is used. The prismatic beam is subjected to four-point periodic sinusoidal bending with free rotation and translation at all load and reaction points. 

Mechanical properties were determined before and after oxidation. Fracture torrghness was determined by means of Vickers indentation method with indentation load in the range 49-196N, whereas thermal shock resistance was determined by water qirenching method in accordance with the standard EN 820-3. Finally, flexiual strength was determined by four-point bend tests at room temperature. Nine samples as bars of 3 x 4 x 45 mm were prepared and tested in accordance with the standard ENV 843-1 (crosshead speed 0.5 mm/min). 

Two methods are used for bend testing—three- and four-point bending tests. Here, the specimens are rectangular, without notches. It is obvious from Fig. 1.48 that the applied force (downward arrows) is compressive by nature, resisted by the tensional force (upward arrows). Thus, the longitudinal stresses at the lower surfaces (convex) in the specimens are tensile and compressive at their upper surfaces (concave). As a consequence, a calculable bending moment develops. The modulus of rupture is the stress of the specimen at its failure and represents the flexural strength of the specimen. 

C848- 76. Young s mouutus was also determined at room temperature by strain gaging a four-point bend specimen. Thermal expansion was measured as a function of temperature with a differential transformer. Thermal conductivity and specific heat were determined as a function of temperature via the laser flash method. ... 

Tests using a constant stress (constant load) normally by direct tension have been described in ISO 6252. This test takes the specimen to failure, or a minimum time without failure, and frequently has a flaw (drilled hole or notch) to act as a stress concentrator to target the area of failure. This type of testing, as well as the constant strain techniques, requires careful control of specimen preparation and test conditions to achieve consistent results (246,247). Use of a slow strain rate with a four-point bend specimen configuration and constant load has been suggested as a method for ranking materials for environmental stress-crack resistance (248). 

The test program was conducted on four-point bend specimens with a root radius of 0.25 mm under a rising step load-displacement controlled test method with the amplitude of the ripple load maintained constant and superimposed at each step load level. The hydrogen charging potential applied during ripple load testing was -1.2 V versus SCE in a 3.5 % salt water environment. 

Another method for characterizing the behaviour of composite elements under load is based on the concept of crack opening displacement (COD). It consists of the measurement of displacements at an initial notch subjected to Mode I of cracking. The characterization of cracking behaviour of materials by COD is possible in LEFM as well as beyond the linear relation for slow crack propagation. The tests are undertaken in three- or four-point bending in displacement-controlled testing machines. However, the COD method does not allow the effective stress concentration to be calculated and may only be used as a valuable comparative measure. 

In addition to monotonic loading conditions, certain repetitive operations could also lead to mechanical failures. A typical example is a PWB used in cell-phone applications. The PWB could be subjected to multiple small deflections each time the ceU-phone keypad is pressed.This can cause an incremental deterioration in the mechanical response of the PWB and lead to solder joint interconnect failures in BG As mounted on the PWB. This sort of failure mechanism is more prevalent in relatively thin PWBs used in cell-phone applications. However, similar failures could also occur if, for example, multiple runs of ICT are performed on PCAs in high-end server/network applications. An industry standard test method has been developed by JEDEC to characterize the response of a PCA to cychc loading conditions (JESD22-B113). The layout of the test board as specified in the test method is similar to that for the monotonic four-point bend test. Some data on the cyclic bend response of Sn AgCu solder joints can be found in Reference 39. 

Table 1. Four point bending strength, fracture toughness measured by single edge pre cracked beam (SEPB) method, and Vickers hardness of the tested alumina specimens. Standard deviations are in brackets.

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