You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Variable impedance actuators: A review 
Chapter Title:  Electrorheological and Magnetorheological Dampers 
1. Abstract of Cited Paper (BIB001):  A novel force/torque control actuator called series damper actuator (SDA) is proposed, modeled and analyzed. Compared to conventional force/torque control schemes and series elastic actuator (SEA), SDA has good output force/torque fidelity, low output impedance and large force/torque range. Furthermore, varying damping coefficient endows the SDA with more advantages and makes the system more versatile. An experimental SDA system is developed, in which a magnetorheological (MR) fluid damper is employed as the series damper. The experimental results show that SDA system is an effective force/torque control actuator. 
2. Abstract of Cited Paper (BIB002):  Abstract A comparison is made of a magnetorheological damper (MRD) and a friction damper (FD) in semi-active suspension design; both devices are closed-loop controlled. Experimentally validated models of both dampers have been developed and a hybrid variable structure-fuzzy control algorithm designed. It is shown that the two devices, albeit based on very different physical principles, can be described by a general common mathematical model, with the FD model being regarded as a particular case of the model for a MRD. The control strategy is targeted to improve occupant comfort. Performance has been investigated numerical simulation in a quarter car vehicle model and compared to that obtained with a classical passive damper. 
3. Abstract of Cited Paper (BIB003):  Research on legged locomotion has encountered its limits in human-made actuation technology. Building a structure and an actuation system capable of performing like a biological muscle for the dynamic locomotion of a mid- to large-sized machine is prohibitive. Novel technologies are being explored with the aim of improving actuator performance. This paper describes the development of a robotic leg for agile locomotion. The main aim is to imitate the multidisciplinary performance of the natural muscle by means of hybridizing conventional and new technologies for the development of large power, large force, lightweight, force-controlled, compliant robotic legs. A preliminary leg prototype has been developed. The actuation system is based on the hybrid use of series elasticity and magneto-rheological dampers which provides variable compliance for natural-looking motion and improved interaction with the ground. Experiments with the real leg prototype provide a positive assessment of the target leg features. 
4. Abstract of Cited Paper (BIB004):  Magneto-rheological (MR) devices, such as dampers, engine mounts and clutches, are now appearing in the ground vehicle industry. Although important work has been directed to assess the longevity of MR dampers, few studies have targeted the aspect of magnetorheological fluid (MRF) durability when used in continuous shear, such as in MR clutches. The objective of this research is to identify the degradation phenomena associated with MRF used in continuous shear and to understand the main causes and effects, in order to propose design improvements to enhance clutch durability. Experiments are conducted on two test benches in order to reproduce MRF aging in a controlled environment and to evaluate the proposed solutions. The effect of the operating conditions (shear rate, shear stress and temperature) on the long term degradation of the torque-current relationship is evaluated. Two degradation phenomena are identified: base oil expansion and particle oxidation. The dominant failure mode of the tested clutches is a MRF leakage resulting from the base oil expansion which occurs between 1.5 MJ/mL and 9 MJ/mL of dissipated energy depending of the operating conditions. Two solutions are proposed to extend clutch durability: 1- MRF circulation and 2-compliant elements.

Literature Review:
Electrorheological (ER) and magnetorheological (MR) dampers (Fig. 11b ) use liquids (Bingham fluids) whose viscosity depends on the electric or magnetic field strength respectively  . The property that can be changed is the yield stress itself. The behavior of ER and MR fluids is given using Bingham viscoplastic models: where g(µ, |q r |) represents the viscous component of the damping force, µ the viscosity of the fluid, u the electric field or the current for ER and MR respectively and C denotes a coefficient that depends on the physical properties of the fluid and on the geometry of the damper. The MR operating principle is often used to realize VDAs in robotics BIB004 [91] BIB002 [92] and also in vehicles BIB001 BIB005 . A more accurate model and a comparison between MR and FD can be found in BIB003 , where it is pointed out that MR dampers, like the FDs, present high hysteresis.