Laminates tensile tests

Mechanical Property Testing. Mechanical tests were performed on both unirradiated and irradiated materials at -157°C, 24°C, and 121°C. Specimens were kept dry prior to testing in an environmental chamber mounted in a tensile testing machine. Tensile test specimens of [0]4, [10]4, [45]4, and [90]4 laminates were cut from 4-ply composite panels. All specimens were straight-sided coupons. For tension and shear tests the length/width aspect ratio was 8. For the compression tests the aspect ratio was 0.25 and the unsupported length was 0.64 cm. The [0]4 laminates were used to measure the ultimate tension and compression strength, Xit the axial... 

In the [ 45]j tensile test (ASTM D 3518,1991) shown in Fig 3.22, a uniaxial tension is applied to a ( 45°) laminate symmetric about the mid-plane to measure the strains in the longitudinal and transverse directions, and Ey. This can be accomplished by instrumenting the specimen with longitudinal and transverse element strain gauges. Therefore, the shear stress-strain relationships can be calculated from the tabulated values of and Ey, corresponding to particular values of longitudinal load, (or stress relations derived from laminated plate theory (Petit, 1969 Rosen, 1972) ... 

The [10°] off axis tension specimen shown in Fig 3.23 is another simple specimen similar in geometry to that of the [ 45 ]s tensile test. This test uses a unidirectional laminate with fibers oriented at 10° to the loading direction and the biaxial stress state (i.e. longitudinal, transverse and in-plane shear stresses on the 10° plane) occurs when it is subjected to a uniaxial tension. When this specimen fails under tension, the in-plane shear stress, which is almost uniform through the thickness, is near its critical value and gives the shear strength of the unidirectional fiber composites based on a procedure (Chamis and Sinclair, 1977) similar to the [ 45°]s tensile test. 

In particular, the techniques based on the termination of certain plies within the laminate has also shown promise. Static tensile tests of [30°/-30°/30°/90°]s carbon-epoxy laminates containing terminals of [90°] layers at the mid-plane show that premature delamination is completely suppressed with a remarkable 20% improvement in tensile strength, compared to those without a ply terminal. Cyclic fatigue on the same laminates confirms similar results in that the laminate without a ply terminal has delamination equivalent to about 40% of the laminate width after 2x10 cycles, whereas the laminates with a ply terminal exhibit no evidence of delamination even after 9x10 cycles. All these observations are in agreement with the substantially lower interlaminar normal and shear stresses for the latter laminates, as calculated from finite element analysis. A combination of the adhesive interleaf and the tapered layer end has also been explored by Llanos and Vizzini, (1992). 

Wide and short samples of [ tensile tested. Some of these samples had a photoelastic resin glued to one side, and the patterns recorded during the test. 

Compression testing is particularly difficult for PMCs due to the occurrence of macro- and microbuckling modes. The rectangular prism specimen in ISO 604 is not suitable for laminated composites, as these will split vertically between the laminate layers when loaded axially in the plane of the laminations. Variations on these designs arc suitable for compression, and tensile testing, in the through-thickness direction (i.e.. direction 3 in Fig. 1),... 

Figure 5.13 Tensile test of a cross-ply laminate. Variation of strain and specimen temperature. Fibre T300, resin LY 556, MY720 (50 50), lay up [Oj, 9O2, O2, 9021s. Load rate = 6.6Nmm s ...

Figure 4.14 shows the failure envelope for the 0° ply constructed from data obtained from a longitudinal tensile test. The failure envelopes for the 90°, -45° and +45° piles are given in Figure 4.14 and are obtained by reflecting the 0° envelope in hnes drawn at +45°, -22.5° and +22.5° to the reference axes system respectively. Finally, the plies in Figure 4.14 are superimposed to obtain the failure envelope for the laminate. 

The tensile test gives mean values for the tensile moduli which are broadly in agreement with values predicted by theory. The values match very well especially for the laminate LI. For the sandwich construction SI and S2 a slight difference appears, perhaps because of their intrinsic structure. Theory therefore provides good estimates for tensile moduli. 

U9an H (2012), Masterbox How to optimize the curing process in the world s biggest laboratory autoclave , JEC Composites Magazine, 72, 38-40 Wisnom M and Hallet S (2009), The role of delamination in strength, failure mechanism and hole size effect in open hole tensile tests on quasi-isotropic laminates . Composites A, 40, 335-342... 

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-... 

Various researchers had found that stalk fibers have better properties than that of the other parts of plant fiber and indicated that they can be used for composite and other industrial applications (Reddy and Yang, 2009). Natural fiber composite laminates with distributed areca and maize stalk fibers using phenol formaldehyde were investigated (Kumar, 2008). Composite laminates were prepared with different proportions of phenol formaldehyde and fibers. Mechanical test such as tensile test, adhesion test, moisture... 

Modulus and Tensile Strength (Tensile Test). The test method to determine modulus and yield stress for copper-clad laminates described in this section is based on ASTM D 882, Standard Test Methods for Tensile Properties of Thin Plastic Sheeting. Other relevant industry standards are IPC-TM-650, method 2.4.19 (for flexible laminate materials), and IPC-TM-650, method 2.4.18.3 (for deposited organic free films). Elastic modulus and yield stress are always determined by the same method. 

Other less well-known types of nonlinearities include interaction and intermode . In the former, stress-strain response for a fundamental load component (e.g. shear) in a multi-axial stress state is not equivalent to the stress-strain response in simple one component load test (e.g. simple shear). For example. Fig. 10.3 shows that the stress-strain curve under pure shear loading of a composite specimen varies considerably from the shear stress-strain curve obtained from an off-axis specimen. In this type of test, a unidirectional laminate is tested in uniaxial tension where the fiber axis runs 15° to the tensile loading axis. A 90° strain gage rosette is applied to the specimen oriented to the fiber direction and normal to the fiber direction and thus obtain the strain components in the fiber coordinate system. Using simple coordinate transformations, the shear response of the unidirectional composite can be found (Daniel, 1993, Hyer, 1998). At small strains in the linear range, the shear response from the two tests coincide. 

What is remarkable is the reduction of tolerable maximum strain after only 105 cycles for the glass fiber-reinforced laminates to only approx. 25% of yield strain in the tensile test. The carbon reinforced laminates still tolerate 75 to 80% of their maximum static strain after 107 cycles, demonstrating their superior cyclic behavior. The aramid fiber-reinforced laminates tolerate only 30% of their maximum static strain after 107 cycles however, they exhibit a striking reduction in maximum strain only at higher cycles of approx. 105. 

Plastics. Only a few plastics have been tested at temperatures below 200 K. Of these, only Teflon showed ductility down to the lowest test temperature, which was 4 K. However, reinforced plastics such as the glass fiber laminates can have good properties, the tensile strength parallel to the laminations increasing at low temperatures and the modulus being approximately constant. Mylar breaks with fragmentation in a tensile test and is correspondingly brittle at low temperatures. Yet in films of about... 

Tensile testing was performed on the laminate coupons in an INSTRON test machine at a displacement rate of 0.2 mm/min (strain rate of approx. 

Tyvek 34g/m samples were prepared by cutting rectangular pieces of dimensions of 0.1524 m x 0.1524 m which were compression molded in varying layer placed biaxially and in a parallel manner and held together by tie layers of thin clear PE film. The laminates were molded at a temperature of 421.48°K, at a 2.2679 kg load for 720 s using a 45359.237 kg compression press machine. Tensile test strip specimens were prepared from the laminates cut at various angles of orientation 0,15,30,45,... 

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. 

The important tensile modulus (modulus of elasticity) is another property derived from the stress-strain curve. The speed of testing, unless otherwise indicated is 0.2 in./min, with the exception of molded or laminated TS materials in which the speed is 0.05 in./min. The tensile modulus is the ratio of stress to corresponding strain below the proportional limit of a material and is expressed in psi (pounds per square inch) or MPa (mega-Pascal) (Fig. 2-7). 

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