			Home About us Contact

Impact Energy (impact + energy)

Distribution by Scientific Domains

Polymers and Materials Science	63%

Selected Abstracts

Microtensile Bond Strength and Impact Energy of Fracture of CAD-Veneered Zirconia Restorations

JOURNAL OF PROSTHODONTICS, Issue 3 2009
Moustafa N. Aboushelib DDS
Abstract Purpose: With state-of-the-art CAD/CAM technology, the fabrication of large and complex zirconia frameworks is just a click away. On the other hand, veneering of the frameworks is still operator-dependent. The aim of this work was to evaluate CAD veneering of zirconia restorations in terms of zirconia veneer bond strength and impact energy of fracture in a step towards complete automation of the fabrication process. Materials and Methods: A new CAD/CAM system was used to fabricate a resin replica of the esthetic ceramic required to veneer a zirconia framework. The replica was seated on the zirconia framework and further processed using press-on technology. The bond strength between zirconia and the CAD veneer was evaluated using microtensile bond strength test. The impact energy of fracture of the specimens was also investigated. Manually layered zirconia specimens served as a control (,= 0.05). Results: There was no significant difference in the microtensile bond strength between zirconia and either of the used veneers (39 MPa). Even though the impact energy of fracture of the CAD-veneered and manually layered specimens was almost identical (0.13 J), the former demonstrated a cohesive fracture of the veneer, while the latter failed by delamination of the veneer ceramic. Conclusion: CAD veneering is a reliable method for veneering zirconia restorations. [source]

Impact behavior of hybrid composite plates

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
Metin Sayer
Abstract This experimental study deals with the impact response of hybrid composite laminates. Two different hybrid composite laminates, aramid/glass and aramid/carbon, and two different stacking sequences, such as [0/0/90/90]A+ [90/90/0/0]G for AG1 and [0/90/±45]A+ [±45/90/0]G for AG2 and so on (see Table I), were chosen for impact testing. The impact energy was gradually increased until complete perforation took place, and an energy profiling method (EPM) was used to identify the perforation thresholds of composites. The damaged samples were visually inspected. The images of the several samples subjected to various impact energies were registered and used for comparison and identifying damage mechanisms. The perforation thresholds for [0/90/±45]s aramid/glass and aramid/carbon laminates were found to be approximately 5% higher than those for their counterparts with the [0/0/90/90]s stacking sequence. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Repeated impact behavior of glass/epoxy laminates

POLYMER COMPOSITES, Issue 11 2009
Bulent Murat Icten
The response of glass,epoxy composites to repeated impact for various impact energies ranging from 5 to 15 J was investigated. Specimens with two different stacking sequences were studied; [0/90/0/90]S and [0/90/+45/,45]S. In addition to the room temperature, impact tests were also performed at ,40°C environmental test temperature for impact energy of 15 J. Contact force-deflection and energy-time curves at each test and the number of impacts to failure (Nf) were obtained for each experiment. Compression after impact (CAI) tests were also conducted to determine the residual load carrying capacity of the damaged specimens. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]

Switching contact task control in hydraulic actuators: Stability analysis and experimental evaluation

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2009
P. Sekhavat
Abstract A switching contact task control for hydraulic actuators is proposed. The controller is built upon three individually designed control laws for three phases of motion: (1) position regulation in free space, (2) impact suppression and stable transition from free to constrained motion and (3) force regulation in sustained-contact motion. The position and force control schemes are capable of asymptotic set-point regulation in the presence of actuator friction and without the complexity of sliding mode or adaptive control techniques. The intermediate impact control scheme is included for the first time to dampen the undesirable impacts and dissipate the impact energy that could potentially drive the whole system unstable. The solution concept and the stability of the complete switching control system are analyzed rigorously using the Filippov's solution concept and the concept of Lyapunov exponents. Both computer simulations and experiments are carried out to demonstrate the efficacy of the designed switching control law. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Preparation and microstructure characterization of ball-milled ZrO2 powder by the Rietveld method: monoclinic to cubic phase transformation without any additive

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2002
S. Bid
The phase transformation kinetics of high-energy ball-milled monoclinic ZrO2 have been studied in detail by Rietveld powder structure refinement analysis. In the present study, no stabilizing compound was required to obtain the cubic phase. The fine-grain powder was milled in a planetary ball mill for up to several hours at different BPMRs (ball to powder mass ratios): 10:1, 20:1, 35:1 and 40:1. During the process of ball milling, the monoclinic phase is gradually transformed to the cubic phase. The relative phase abundances of the respective phases, the particle sizes, the r.m.s. strains, the lattice parameter changes, etc., have been estimated from Rietveld analysis of X-ray powder diffraction data. It has been found that a higher BPMR exerts more influence on rapid phase transformation. In the m - to c -ZrO2 phase transformation, no formation of an intermediate tetragonal ZrO2 phase has been found. The small change in the lattice volume of m -ZrO2, which is very close to the lattice volume of c -ZrO2, caused by ball milling may be attributed to this phase change. The formation of the c phase is noticed, in general, after just 1,h of ball milling, and the particle size of the m phase is reduced to a large extent at the first stage of milling and remains almost unchanged with increasing milling time. However, the particle size of the c phase increases with increasing milling time for the samples milled with higher BPMRs (35:1 and 40:1), suggesting that quenching caused by a high impact energy followed by an annealing effect may play a vital role, which is further manifested in the agglomeration of small particles. [source]

Microtensile Bond Strength and Impact Energy of Fracture of CAD-Veneered Zirconia Restorations

Damage Phenomena Observed on PVD Coatings Submitted to Repeated Impact Tests

PLASMA PROCESSES AND POLYMERS, Issue S1 2007
Florent Ledrappier
Abstract Thin hard coatings obtained by PVD process are widely used to improve the mechanical and friction behaviour of industrial parts. Depending on the friction conditions, the failure mechanisms and resulting selection criteria may be very different. This study aims to investigate the endurance life of some PVD coatings under repeated impact conditions. Impact tests at controlled impact energy have been performed using a hemispherical tip. Long-term tests have been done to determine the coating endurance life while short tests enable us to identify the damage phenomena. Depending on the nature of the PVD coating, cracks, blisters or spalling may be observed under impact. These phenomena may worsen until the complete film rupture occurs. [source]

Repeated impact behavior of glass/epoxy laminates

Effect of high-energy vibro-milling of filler on the mechanical properties of filled high-density polyethylene

POLYMER COMPOSITES, Issue 3 2003
Shaoyun Guo
The effect of high-energy mechanical milling of CaCO3 (calcium carbonate) and STC (a mixture of sericite, tridymite and cristobalite) on mechanical properties, rheological and dynamical mechanical behavior of high-density polyethylene (HDPE)/CaCO3 and HDPE/STC was studied through SEM (scanning electron microscope), DMTA (dynastic mechanical test analysis), mechanical and melt rheological properties tests. The experimental results show that addition of fillers treated by coupling agent and vibromilling to HDPE makes the impact strength of HDPE greatly increased. The impact strength of HDPE/treated CaCO3 (60/40) and HDPE/treated STC (60/40) is ca. 4 and 3 times respectively as high as that of HDPE. The SEM micrographs of impact fractured surfaces of treated fillers filled HDPE show extensive plastic deformation of HDPE matrix, indicating that the plastic deformation of matrix induced by the treated fillers is the main contribution for absorbing a great amount of impact energy. This is the reason why the impact strength of HDPE greatly increases with addition of coupling agent and vibromilling treated fillers. The intensity of , relaxation peak of HDPE in HDPE/treated CaCO3 on tan, vs. temperature curve increases and the peak shifts to higher temperature due to its stronger interface interaction as compared with that of HDPE/untreated CaCO3. [source]

Composites from PMMA modified thermosets and chemically treated woodflour

POLYMER ENGINEERING & SCIENCE, Issue 5 2003
Betiana A. Acha
The mechanical behavior of composites made from woodflour and a modified thermoset unsaturated polyester resin has been examined. Polymethylmethacrylate (PMMA), a common low profile additive (LPA), was used as the matrix modifier. Woodflour, the reinforcing filler, was used ,as received' and was also modified with a commercial alkenyl succinic anhydride (ASA), in order to enhance the compatibility with the resin. The composites exhibited higher flexural and compressive modulus and compressive yield stress than the neat resin, while flexural strength and ultimate strain were reduced. The addition of PMMA to the unfilled thermoset led to a LPA morphology and decreased the flexural modulus, but produced an increment in flexural strain at break, impact energy and toughness of the UP resin. No enhancement in the mechanical behavior of the composites was found when treated woodflour instead of unmodified woodflour was used. [source]

Intraply and interply hybrid composites based on E-glass and poly(vinyl alcohol) woven fabrics: tensile and impact properties

POLYMER INTERNATIONAL, Issue 9 2004
Prof Alessandro Pegoretti
Abstract E-glass and poly(vinyl alcohol) (PVA) fibres were used to produce both homogeneous and hybrid composites with an orthophthalic unsatured polyester resin. Results are presented regarding the tensile and impact behaviour of both intraply and interply hybrid composites, with particular regard to the effects of the plies stacking sequence and the loading direction. With a proper choice of composition and stacking sequence, E-glass/PVA hybrid composites were proved to achieve a property profile superior to those of homogeneous E-glass laminates in terms of specific properties. In particular, hybridization with PVA fibres resulted in improving the specific impact energy of E-glass laminates. Resistance to impact crack propagation was higher for intraply with respect to interply hybrid composites, as evidenced by their ductility index values. Copyright © 2004 Society of Chemical Industry [source]