Another viscoelastic model is derived, by combining a spring and a dash- pot in parallel. This is named after Voigt (or Kelvin] and shown in Figure 4-13. (Numbers 1 and 2 refer to the spring and the dash-pot, respectively.) A constant load (stress Sol is applied and as a result the whole body will stretch. However, the spring cannot respond immediately as it is connected to the dash-pot in a rigid manner. Therefore, there will be a retarded but final elastic deformation (damped). On removal of the load, the deformation will reverse, still retarded (time-dependent). The strain r is identical in both ele- ments, but the stress is divided between them. This is shown in Figure 4-14. The initial deformation is characterized by a positive slope that gradually diminishes, eventually reaching a plateau which is determined by the ulti. mate deformation of the spring. If at tt the load is removed, the deformation
at this stage will recover completely but gradually. This model is therefore considered to represent the total recovery of a viscoelastic solid responses are in engineering practice as creep and recovery, met These and are considered to be of paramount importance when dealing with the mechanical performance of plastic materials under extended period of static loading. As in the case of stress-relaxation, this behavior is controlled a characteristic material parameter called the retardation time (A nIG). The history of creep and recovery may also be traced by a time-dependent compliance, J(t 1IGIt) (4-13) Real materials exhibit a much more complex behavior compared to these simplified linear viscoelastic models. One way of simulating increased com- plexity is by combining several models If, for instance, one combines in series a Maxwell and a Voigt model, a new body is created, called the Burger model (Figure 4-15) We choose to separate the spring and the dash-pot from the Maxwell element, which does not affect the result. There are four basic parameters: G1, 2, n2 and 13. On stretching, due to application of a load, the response may be attributed to three elements- the single spring, the Voigt element and the single dash-pot. The response of the single spring is instantaneous according to Hooke's law. This represents the glassy state a quick response in a short time or a low temperature. The Voigt element contributes retarded elasticity and the combination acts as an elastic solid susceptible to creep under load. The single dash-pot is a flow element, making the combined body a viscoelastic liquid with some portion of unrecovered deformation Y1. All this is shown in Figure The represents the behavior above T, in the elastomeric state, while the single at temperatures Around the transition between the glassy and states, elasticity drops 10" fold, and the material becomes flexible and
Another viscoelastic model is derived, by combining a spring and a dash- pot in parallel. This is named after Voigt (or Kelvin] and shown in Figure 4-13. (Numbers 1 and 2 refer to the spring and the dash-pot, respectively.) A constant load (stress Sol is applied and as a result the whole body will stretch. However, the spring cannot respond immediately as it is connected to the dash-pot in a rigid manner. Therefore, there will be a retarded but final elastic deformation (damped). On removal of the load, the deformation will reverse, still retarded (time-dependent). The strain r is identical in both ele- ments, but the stress is divided between them. This is shown in Figure 4-14. The initial deformation is characterized by a positive slope that gradually diminishes, eventually reaching a plateau which is determined by the ulti. mate deformation of the spring. If at tt the load is removed, the deformation at this stage will recover completely but gradually. This model is therefore considered to represent the total recovery of a viscoelastic solid responses are in engineering practice as creep and recovery, met These and are considered to be of paramount importance when dealing with the mechanical performance of plastic materials under extended period of static loading. As in the case of stress-relaxation, this behavior is controlled a characteristic material parameter called the retardation time (A nIG). The history of creep and recovery may also be traced by a time-dependent compliance, J(t 1IGIt) (4-13) Real materials exhibit a much more complex behavior compared to these simplified linear viscoelastic models. One way of simulating increased com- plexity is by combining several models If, for instance, one combines in series a Maxwell and a Voigt model, a new body is created, called the Burger model (Figure 4-15) We choose to separate the spring and the dash-pot from the Maxwell element, which does not affect the result. There are four basic parameters: G1, 2, n2 and 13. On stretching, due to application of a load, the response may be attributed to three elements- the single spring, the Voigt element and the single dash-pot. The response of the single spring is instantaneous according to Hooke's law. This represents the glassy state a quick response in a short time or a low temperature. The Voigt element contributes retarded elasticity and the combination acts as an elastic solid susceptible to creep under load. The single dash-pot is a flow element, making the combined body a viscoelastic liquid with some portion of unrecovered deformation Y1. All this is shown in Figure The represents the behavior above T, in the elastomeric state, while the single at temperatures Around the transition between the glassy and states, elasticity drops 10" fold, and the material becomes flexible and
การแปล กรุณารอสักครู่..