Quasi-static mechanical testing

Table 47.2 lists the Qj (in GPa) for human (haversian) bone and bovine (both haversian and plexiform) bone. With the exception of Knefs [1978] measurements, which were made using quasi-static mechanical testing, aH the other measurements were made using bulk ultrasonic wave propagation. 

The main dilferences between conventional quasi-static mechanical testing and a dynamic impact event on large samples have been well demonstrated in the open literature. Generally, the strain rate for quasi-static mechanical testing is on the order of lO -lO s while dynamic testing is in the range of 10 -10" s Therefore, the stressed volume in an impact event is much larger than that in the... 

Quasi-static mechanical tests of extruded and drawn blends, as well as MFCs based on PET, PBT, PAG, PA66 and of the neat polymers are shown in Figure 11.7 [41,42,45,90]. 

Cycloolefin copolymer (COC) is an amorphous, clear metallocene product of norbomene and ethylene with a spectrum of attractive performance characteristics. Thus, COC (MFI at 190 °C and 2.16 kg = 1.7 dg min, p = 1,020 kg m ) was blended with C2+6 LLDPE (MFI at 190 °C and 2.16 kg = 3.2 dg min , p = 920 kg m ). The mechanical properties of the blends indicate immiscibility, despite the increased LLDPE crystallinity. The presence of COC improved the thermo-oxidative stability. Quasi-static tensile tests showed that increasing fraction of COC in the blends accounts for an enhancement of the elastic modulus and a decrease in the strain at break, while tensile strength passes through a minimum. A significant reduction of the creep compliance of LLDPE could be achieved only for the COC fractions exceeding 20 wt% (Dorigato et al. 2010). 

Testing Conditions and Analysis. The fracture behavior was investigated at room temperature at nominal piston velocities, from 10-4 m/s to 10 m/s. For test speeds higher than 10-1 m/s, the damped test procedure described in reference 15 was used. Quasi-static stress conditions therefore prevailed in the specimen, even at high loading rates. This fact allowed the analysis of fracture-mechanics parameters to be performed using a static approach. 

Although bone is a viscoelastic material, at the quasi-static strain rates in mechanical testing and even at the ultrasonic frequencies used experimentally, it is a reasonable first approximation to model cortical bone as an anisotropic, linear elastic solid with Hooke s law as the appropriate constitutive equation. Tensor notation for the equation is written as ... 

A peroxide-induced reactive compounding of PP/GRT blends in a corotating twin-screw extruder was carried out to prepare thermoplastic elastomer alloys (Wiessner et al., 2012). The extrusion experiments showed that the width of the residence time distribution was the key parameter determining the mechanical properties of elastomer alloys, whereas the mean residence time had little effect. This was confirmed by performing both quasi-static and cyclic tensile tests. 

Table 8.1 Quasi-static fracture mechanics test methods for FRP composites...

The literature published on fracture mechanics testing of FRPs in the last 40 years comprises a large database on delamination resistance or fracture toughness of different types of FRPs. An early review [51] compiled the data available at that time. Selected data from quasi-static mode I and mode II tests on FRPs were compared by O Brien [52], and quasi-static mode I test data from carbon—fibre epoxy and poly-ether-ether-ketone (PEEK) by Brunner [53]. Mechanical properties of FRP composites are compiled in the Composite Materials Handbook version F (2002) [9—11], but this does not comprise fracture mechanics data. Hence, there is no comprehensive and up-to-date database on the available data or literature. 

For certain products long time dynamic (creep, fatigue, impact, etc.) mechanical load performances in different environments are required. Dynamic loading in the present context is taken to include deformation rates above those achieved on the standard laboratory-testing machine (commonly designated as static or quasi-static just reviewed). These slower tests may encounter minimal time-dependent effects, such as creep and stress-relaxation, and therefore are in a sense dynamic. Thus the terms static and dynamic can be overlapping. 

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