Force-clamp mode

The time-dependence of the force is determined by the protocol applied in the actual application of DFS. One common way to perform the experiments or simulations is the force-ramp mode, in which the applied force increases with a constant velocity, F t) = where k denotes the force constant of the pulling device. The other protocol, called force-clamp mode, crmsists in the application of a constant external force, F(t) = Fext- In the force-ramp case, one finds the logarithmic dependence of the mean rupture force and v quoted above. The simple model appears to work quite well for small pulling velocities but fails if one pulls fast. In this simation, more detailed calculations of the rupture force distributions via the computation of the mean first passage time in model free-energy landscapes give more reliable results [104]. 

If the reversible dynamics of bond rupture is considered in the force clamp mode, one can exploit an analogy to the treatment of single molecule fluorescence to treat the statistical properties of the transition events [108, 109]. If one considers two states, A (closed) and B (open) with rates k, = k(A —> B) and = (B A), the equilibrium constant is given by = A b/ a- Due to the strong exponential dependence of the kinetic rates on the external force, in the Bell model given by a( ) = and k F) = one can vary Kover a broad range. This... 

The DMA characterization was made of the series of polymers denoted PU 1 to PU 5 as listed in Table 3.11. The samples were tested in the tensile mode with a starting distance between the clamps of 45 mm. The cooling conditions were room temperature till -60°C cooling rate of 10 K/minute, -60°C to -120°C 3.5 K/min and -120°C to -140°C 2 K/min. The test started at -140°C and the complex modulus , storage modulus loss modulus E" and the loss factor were measured as function of temperature at a heating rate of 1 K/min. The instrument was operated with controlled sinusoidal force with a frequency of 1 s ... 

Ceramic Metal Composites. Ceramic metal composites are characterized by a simple design and extreme robustness. This is achieved by the combination of an active ceramic with metal clamping plates (shells or caps). The metal plate is used to achieve the coupling of the active ceramic to the surrounding medium. The metal plate is a mediator or coupler between the operating force and the ceramic. The best ceramic metal composite sensors are the flextensional type transducers. For this construction the flexural modes... 

A certain period at 20 or 23°C must elapse before testing, in order to standardize the test specimen. Then the test specimen is clamped in a tensile machine, such as the one shown in the colour section, and pulled with a constant rate of increase of the pull force, until it breaks, and the forces are recorded. The mode of rupture, adhesive or cohesive or mixed, is also carefully noted (Fig. 29b). 

Thermomechanical Analysis (TMA) measures unidirectional dimensional changes in materials as functions of time, temperature and applied force. The TMA measurements are coefficient of linear thermal expansion (CLTE), glass transition temperatures (Tg) and softening points (Ts). Newer applications of TMA include elasticity, melt viscosity, and heat deflection temperature. In addition to traditional TMA instruments, many modem dynamic mechanical thermal analysis (DMTA) instruments can operate in a TMA (static force) mode. The main differences between the two types of instruments are the size of the specimens and the materials used to fabricate the measurement fixtures (stage, probe, clamps, etc.). Most TMA instruments use quartz, while DMTA instruments use larger steel components. The specimens used in these experiments are... 

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