Laminates flexural tests

Flexure testing (ASTM D790-76) was performed on 12 ply unidirectional laminates with the fibers oriented at 0° and 90° to the support span. Specimens were 25 mm wide, nominally 100 mm long and tested at a span-to-thickness ratio of 32 1. The specimens were three point loaded and the rate of strain in the outer fibers was kept constant at 0.01 (mm/min) per min. Load vs. deflection curves were recorded for determination of the modulus and yield properties. 

In the broad sense, interlaminar adhesion means the adhesion between any laminations of similar or dissimilar materials and hence could be taken to include just about any adhesion test. One particular type for fiber-reinforced plastics, which is known as interlaminar shear strength, is normally considered as a short beam flexural test (sec Chapters 9 and 18). A method peculiar to laminated plastics tube is given in BS 2782, Method 346A [59] and called cohesion between layers of laminated tube. A sample of tube is subjected to compression to induce shear forces between layers and delamination observed by eye,... 

Horiguchi K, Shindo Y, Kudo H, Kumagai S. End-notched flexure testing and analysis of mode U interlaminar fiacture behaviour of glass-cloth/epoxy laminates at cryogenic temperatures. J Compos Technol Res 2002 24 239-45. http //dx.doi.org/10.1520/CTR10930J. 

Table 17.10 Dimensions and test conditions for flexure tests based on a laminate thickness of 2 mm...

In this chapter, results from the tensile, flexural and impact tests on HDPE/PA6 and HDPE/PA12 MFC are presented, studying the effects of the compatibilizer, HDPE and PA concentration, as well as the form and arrangement of the reinforcing entities on the mechanical behavior. The UDP MFC laminae were used for tensile tests. Impact strength and three-point flexural tests were performed on the CPC laminates. MRB and NOM composites were analyzed with the three mechanical tests. The data were compared with those of the neat HDPE matrix material and/or the oriented polyamide component [69]. 

In practice, only in very few cases do materials work in tensile mode more often they are subjected to flexure or impact. On the other hand, fiber-reinforced composites are usually applied as laminates with different orientation and alignment of the fibrous reinforcement. That is why the CPC laminates were used to study their flexural stiffness and impact resistance. The flexural tests were performed by the threopoint support test method used by Nunes et al, as shown in Figure 14.6 [74]. The support was mounted in the same Instron machine used for the tensile tests, this time operating in compression mode. Rectangular samples (155 x 100 mm) were cut out from the CPC MFC plates and placed upon the sup-... 

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

Figure 8. Photographs of 0 bare (water-sized) E-glass fiber laminates tested in flexure showing the tensile side of the specimen. The tensile side fibers failed first, then propagated delaminations along the tensile surface of the specimen.

D 1184 Test Method for Flexural Strength of Adhesive Bonded Laminated Assemblies... 

For the three-point bending test of the sixth plys laminate panels, the flexural strength of the PTFE / FP composite was about 2.9 times higher than that of the PTFE composite. Moreover, the flexural modulus of the PTFE / FP... 

Table III shows the flexural properties of RX-PTFE composite with an EB dose of 500 kGy and SX-PTFE composite (fluorinated-pitch 1.8 wt% additive) with an EB dose of 500 kGy. For the three-point bending test of the sixth plys laminate panels, the flexural strength of SX-PTFE composite was about 1.1 times higher than that of the RX-PTFE composite. The flexural modulus of SX-PTFE composite was about 1.3 times higher than that of RX-PTFE composite. It was found that the flexural properties of SX-PTFE were improved, compared with RX-PTFE composite.

The apparent inierlantinar shear lest uses a short beam flexure loading mode to measure the shear strength along the plane of lamination. The analysis of the test is... 

Fracture toughness tests for isotropic materials normally use edge-notched flexure beams and compact tension specimens. These methods are. as for the impact tests, only suitable for the injected or compression molded materials, which do not have a strongly laminated structure. Laminated composite materials have their primary failure path between the layers, and a new set of test geometries has been developed. 

Davies et al. [64] studied the influence of water absorption on the interlaminar shear strength and end notch flexure (ENF mode II shear) fracture toughness of quasi-unidirectional (88% 0°, 12% 90°) E-glass fibres in DGEBA epoxy resin cured with an amine hardener. Laminates were immersed in (a) distilled water and (b) the Atlantic Ocean ( at Boca Raton, Florida) for up to 8 months at temperatures of 20°C, 50°C and 70°C. Sea water was more slowly absorbed than distilled water. This observation has frequently been made and it provides some reassurance that laboratory tests using distilled water are useful, if slightly cautious, estimates of behaviour in the ocean. 

The reliability of this real life experience is corroborated by the results of laboratory research. American Society for Testing and Materials (ASTM) C581 [6] is designed to reflect the resin deterioration when a laminate is totally immersed in a corrosive medium. Central to the procedure is the strict specification of a standard laminate and of standard conditions for exposing samples to corrosive liquids. The method specifies determining the hardness and flexural properties of the laminates at 1, 3, 6 and 12 months. 

The laminates of tiK carbon-fiber composite were first characterized by acoustic NDI (C-scan) and optical microscopy to evaluate their quality. Scanning electron microsctqiy (SEM) was used to evaluate laminate quality and nanoparticle distributimi using a Philips XL30 ESEM TMP scanning electron microscope. Mechanical tests fm tiie carbon-fiber composite were selected to measure resin-dominated properties. These tests were transverse four-point flexure with a qian-to-deptii ratio of 32 1 and longitudinal four-point flexure with a qi>an-to-depdi ratio of 16 1 designed to induce mic lane shear failure. Ten qiecimens were tested for each material type and condition. 

ASTM D1184-98 Standard test method for flexural strength of adhesive bonded laminated assemblies. 

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