Search

In many practical applications rubber components are exposed to relatively high operating temperatures yet very few studies can be found in the literature that deal with the temperature influence on deformation and, especially, failure of rubberlike materials. In the present work, we partly fill this gap providing the experimental results on uniaxial tension and bulge tests for nitrile butadiene rubber, neoprene, and silicone for various temperatures in the range from 20°C to 90°C. Based on the results of the tests we develop novel thermoelastic constitutive models, which also incorporate a failure description via the method of energy limiters. Using the developed models, we study the cavitation problem under the elevated temperatures. We find that, generally, the heating might lower material strength while the material stiffness is not necessarily sensitive to the temperature alterations.

Rubber-like materials are widely used in several industrial applications. In these applications, rubber components are largely subjected to biaxial loading at a range of temperatures. In this work, we study the effect of short-term temperature on the ultimate properties of rubber materials, particularly, their strength. Such studies are lacking in the literature. For this purpose, we consider three different rubber-like materials; Nitrile Butadiene Rubber (NBR), Neoprene and Silicone. These rubber materials are tested under equi-biaxial tension using the bulge test. Tests are conducted till failure under a constant temperature. Four different temperatures are considered; 25 ∘C, 50 ∘C, 70 ∘C and 90 ∘C. Experiments are modeled using a finite element method. A constitutive model which includes the description of failure through energy limiters is calibrated against the bulge experiments. It is found that while the material stiffness is not significantly affected by temperature the ultimate stress and stretch, as well as the energy limiter for NBR and Neoprene greatly depend upon temperature. Stress carrying capacity for NBR and Neoprene decreases drastically at the highest temperature considered as compared to their values at room temperature (25 ∘C). Properties of Silicone are not affected significantly because of its temperature resistance. A new constitutive function is developed for the energy limiter, which allows unifying the description of different materials.

Fracture toughness of the brittle amorphous polymer polymethyl methacrylate (PMMA) has been reported to decrease with loading rate at moderate rates and increase abruptly thereafter to close to 5 times the static value at very high loading rates. Dynamic fracture toughness that is much higher than the static value has attractive technological possibilities. However, the reasons for the sharp increase remain unclear. Recent work on another amorphous polymer, Polycarbonate (PC), has shown that the existence of this phenomenon depends sensitively on the definition of the term “fracture initiation”. Difficulties associated with the visualisation of the very early stages of defect nucleation constrain us to use indirect pointers to determine fracture initiation. Following on the work of Faye et al. (2015) on PC, we have (i) used ultra high speed imaging to time very early stages of defect nucleation ahead of a notch, and, (ii) concurrently conducted Finite Element simulations using a well-calibrated viscoelastic model for PMMA, in order to gain insights into the phenomenon of amplification of fracture initiation toughness at high loading rates. Our results suggest that toughness at the initiation of early defects in PMMA is somewhat lower at high loading rates. It seems that toughness amplification results from use of either surface gauges or the attainment of maximum load as indication of crack initiation. The fact that the crack front in PMMA may not be perfectly straight leads to a lower value of initiation toughness.

Polycarbonate (PC), which is considered to be a ductile amorphous polymer, is prone to brittle fracture in the presence of sharp notches. In the present work, effect of notch-tip radius on brittle fracture of PC is studied under static and under dynamic loading (high loading rates) conditions. Towards this end, a hybrid experimental and numerical approach is adopted. Dynamic fracture experiments using Hopkinson bar setup are performed on single-edge notched specimen of PC having different notch-tip radii. Ultra-high speed imaging is used for real-time observation of the fracture process. Finite element simulations are simultaneously performed using a well calibrated elastic-viscoplastic constitutive model for polymers. In the presence of a notch, brittle fracture in PC starts with a defect nucleation ahead of it. For each notch-tip radii, we are experimentally able to capture the process of defect initiation and quantify the mean stress required, static as well as dynamic loading. We found that the mean stress required for defect nucleation increases with decreasing notch-tip radius due to increased triaxility at the notch-tip. Defect initiation stresses are also higher for dynamic conditions compared to static loading. Defect initiation toughness for dynamic loading is always higher than those for static loading, but reduction in defect initiation toughness with decreasing notch-tip is severe for dynamic loading.

Phase-field or gradient-damage approaches offer elegant ways to model cracks. Material stiffness decreases in the cracked region with the evolution of the phase-field or damage variable. This variable and, consequently, the decreased stiffness are spatially diffused, which essentially means the loss of the internal links and the bearing capacity of the material in a finite region. Considering the loss of material stiffness without the loss of inertial mass seems to be an incomplete idea when dynamic fracture is considered. Loss of the inertial mass in the damaged material region may have significant effect on the dynamic failure processes. In the present work, dynamic fracture is analyzed using a theory, which takes into account the local loss of both material stiffness and inertia. Numerical formulation for brittle fracture at large deformations is based on the Cosserat point method, which allows suppressing the hourglass type deformation modes in simulations. Based on the developed algorithms, the effect of the material inertia around a crack tip is studied. Two different problems with single and multiple cracks are considered. Results suggest that in dynamic fracture the localized loss of mass plays an important role at the crack tip. It is found, particularly, that the loss of inertia leads to lower stresses at the crack tip and, because of that, to narrower cracks as compared to the case in which no inertia loss is considered. It is also found that the regularized problem formulation provides global convergence in energy under the mesh refinement. At the same time, the local crack pattern might still depend on the geometry of the unstructured mesh.

Fracture toughness of brittle amorphous polymers (e.g. polymethyl methacrylate (PMMA)) has been reported to decrease with loading rate at moderate rates and increase abruptly thereafter to close to 5 times the static value at very high loading rates. Dynamic fracture toughness that is much higher than the static values has attractive technological possibilities. However, the reasons for the sharp increase remain unclear. Motivated by these observations, the present work focuses on the dynamic fracture behavior of polycarbonate (PC), which is also an amorphous polymer but unlike PMMA, is ductile at room temperature. Towards this end, a combined experimental and numerical approach is adopted. Dynamic fracture experiments at various loading rates are conducted on single edge notched (SEN) specimens with a notch of radius 150 μ m , using a Hopkinson bar setup equipped with ultra high-speed imaging ( > 10 5 fps ) for real-time observation of dynamic processes during fracture. Concurrently, 3D dynamic finite element simulations are performed using a well calibrated material model for PC. Experimentally, we were able to clearly capture the intricate details of the process, for both slowly and dynamically loaded samples, of damage nucleation and growth ahead of the notch tip followed by unstable crack propagation. These observations coupled with fractography and computer simulations led us to conclude that in PC, the fracture toughness remains invariant with loading rate at J frac = 12 ± 3 kN / m for the entire range of loading rates ( J ) from static to 1 × 10 6 kN / m − s . However, the damage initiation toughness is significantly higher in dynamic loading compared to static situations. In dynamic situations, damage nucleation is quickly followed by initiation of radial crazes from around the void periphery that initiate and quickly bridge the ligament between the initial damaged region and the notch. Thus for PC, two criteria for two major stages in the failure process emerge. Firstly, a mean stress based defect initiation is suggested. The value of the critical mean stress for defect initiation under dynamic loading is found to be 115±5 MPa, which is significantly higher than its static value of 80 MPa. The critical normal plastic stretch needed for crazes to nucleate from the nucleated defect is estimated to be about 1.78±0.2.

Dynamic cavitation is known to be a typical failure mechanism in rubber-like solids. While the mechanical behaviour of these materials is generally rate-dependent, the number of theoretical and numerical works addressing the problem of cavitation using nonlinear viscoelastic constitutive models is scarce. It has been only in recent years when some authors have suggested that cavitation in rubber-like materials is a dynamic fracture process strongly affected by the rate-dependent behaviour of the material because of the large strains and strain rates that develop near the cavity. In the present work we further investigate previous idea and perform finite element simulations to model the dynamic expansion of a spherical cavity embedded into a rubber-like ball and subjected to internal pressure. To describe the mechanical behaviour of the rubber-like material we have used an experimentally calibrated constitutive model which includes rate-dependent effects and material failure. The numerical results demonstrate that inertia and viscosity play a fundamental role in the cavitation process since they stabilize the material behaviour and thus delay failure.

Fracture toughness of brittle amorphous polymers (e.g. PMMA) has been reported to decrease with loading rate at low rates and increase abruptly to close to 5 times its static value at very high loading rates. Dynamic fracture toughness that is much higher than the static values has attractive technological possibilities. However, the reasons for the sharp increase remain unclear. Motivated by these observations, the present work focuses on the dynamic fracture behavior of Polycarbonate (PC), which is also an amorphous polymer but unlike PMMA, is ductile at room temperature. The objective of this paper is to investigate if PC also shows a behavior similar to PMMA, with a view to understanding the mechanics of the increase. Towards this end, a combined experimental and numerical technique is adopted. Dynamic fracture experiments at varying loading rates are conducted on single edge notched (SEN) specimens using Hopkinson bar with ultra high speed imaging (> 105 fps) to observe dynamic processes during fracture. Concurrently, 3D dynamic finite element simulations are performed using a well calibrated material model for amorphous polymers. Based on the experimental observation and numerical studies, mechanics behind dynamic fracture in PC is explained in detail. It has been concluded that the final fracture toughness remain invariant with loading rate. However, the void initiation toughness is higher in dynamic loading compared to that in static, due to rapid expansion of void leading to radial crazes emanating from it. With further studies on void dynamics, a mean stress based criterion for void initiation and then plastic strain based criterion for final fracture of PC is also established.

This article deals with the active structural-acoustic control of thin laminated composite plates using vertically reinforced 1–3 piezoelectric fiber-reinforced composite (PFRC) material for constraining layer of active constrained layer damping (ACLD) treatment. A finite element model is developed for the laminated composite plates integrated with ACLD patches and coupled with acoustic cavity to describe the coupled structural-acoustic behavior of the plates enclosing the cavity. Both in-plane and out of plane actuation of the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. The analysis revealed that the vertical actuation dominates over the in-plane actuation. The performance of PFRC layers of the patches has been investigated for active control of sound radiated from thin symmetric and antisymmetric cross-ply and antisymmetric angle-ply laminated composite plates into the acoustic cavity.

The fracture behavior of notched polycarbonate (PC) is investigated as a function of loading rate ranging from quasistatic to dynamic. Complementary numerical simulations are performed using the experimentally obtained load-point displacement as the input. The results indicated that in the rage of loading rates considered, the fracture initiation toughness of PC is not sensitive to loading rate. The fracture processes near the dynamically loaded notch-tip was observed using ultra-high speed imaging. In both quasi-static and dynamic loading, defects nucleate ahead of the notch tip and coalesce before final fracture. In quasi-static tests there is considerable time lag between defect nucleation and final fracture, whereas in dynamic experiments the two are almost synchronous.

Accurate estimation of dynamic fracture properties of materials is important for component design under impact conditions. Amorphous glassy polymers have wide engineering applications. For Polymethyl methacrylate (PMMA), which is a brittle amorphous polymer, literature indicates that the fracture toughness increases at higher loading rates compared to that under static loading conditions. Motivated by this observation, in the present work, another amorphous polymer named Polycarbonate (PC), which is ductile in nature, is considered and effect of loading rate on fracture toughness of PC is investigated. Experiments using the single edge notched (SEN) specimen subjected to 3-point bending are performed at various loading rates. A UTM is used for low loading rate experiments. High loading rate experiments are conducted using Hopkinson pressure bar. Ultra high speed imaging (100,000 fps) is used to make accurate measurement of fracture initiation time in these experiments. Attempts are being made to investigate the near notch deformation in detail. A hybrid experimental and numerical approach is pursued in which finite element simulations are performed using the boundary conditions obtained from experiments. A rate and temperature dependant constitutive model is used for PC. Stress intensity factor (SIF), evaluated from simulation is correlated with experimentally measured SIF. Results show that that dynamic fracture initiation toughness of PC does not vary significantly at higher loading rates; values remain close to that obtained under quasi-static loading conditions.

This paper deals with investigations on the active structural–acoustic control of a thin homogeneous isotropic plate using vertically reinforced 1-3 piezoelectric composite (PZC) material. A finite element model is developed for the plate which is integrated with a patch of active constrained layer damping (ACLD) treatment and coupled with an acoustic cavity to describe the coupled structural–acoustic behavior of the plate. The constraining layer of the ACLD treatment is composed of the vertically reinforced 1-3 PZC material. Both in-plane and out-of-plane actuations by the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. An experiment is also carried out to investigate the performance of the patch of the ACLD treatment in which the constraining layer of the patch is made of vertically reinforced 1-3 PZC for active structural–acoustic control of the plate. Both the finite element analysis and the experimental investigation agree with each other and reveal that the vertically reinforced 1-3 PZC material performs excellently for achieving active structural–acoustic control of the isotropic plate.