Photoelastic Stress Patterns Research Articles

Interfacial shear strength studies of experimental carbon fibres, novel thermosetting polyurethane and epoxy matrices and bespoke sizing agents

The strength and nature of the fibre-matrix connection affects many of the key mechanical characteristics of composite parts. The complex interplay of fibre surface, sizing agent and matrix material has been a longstanding problem and receives substantial attention when new ingredients are introduced. For the first time, this study investigated a novel thermosetting polyurethane resin together with a set of experimental carbon fibres. The fibres were manufactured using a unique facility that closely models a commercial production line. This equipment allowed extracting fibres after carbonisation, after electrochemical surface treatment and after coating with epoxy, polyurethane and polyamide based sizing agents. A commercial carbon fibre and a state of the art epoxy resin were selected as reference materials. The single fibre fragmentation test was used to measure the interfacial shear strength (IFSS) of the resulting combinations. The results show the enormous importance of etching away the relatively inert outer layer during surface treatment as the IFSS increased by factor 2.6. The newly developed polyurethane resin showed for unsized fibres up to 50% higher values for the IFSS than corresponding combinations employing epoxy resin. This superiority melted down to 5–21% when looking at the sized fibres, showing the need for developing sizing agents that facilitate adhesion to polyurethane matrices. A relative advantage of identical sizing and matrix polymer could be found when looking at sized fibres. Photoelastic investigations of the fragmented specimens supported the measured values for the IFSS. There was a close correlation between high IFSS results and strong photoelastic stress patterns.

Photoelastic stress analysis of mandibular fixed prostheses supported by 3 dental implants.

To observe the photoelastic stress patterns generated around implants in relation to variations in the diameter and total number of implants supporting fixed complete-arch mandibular frameworks. Three different implant configurations were analyzed (n = 3): 5 standard implants with diameters of 3.75 mm (C), 3 standard implants with diameters of 3.75 mm (3S), and 3 wide implants with diameters of 5.0 mm (3W). The samples were subjected to a vertical compressive load (1.33 kgf) applied at the end of the distal cantilever of the framework. The shear stresses were calculated around the implants, and the data were analyzed using one-way analysis of variance. The implants nearest to the loading showed higher stress values regardless of the group. The C group showed lower shear stress when compared with the other groups (P = 0.001). No significant difference was observed between the 3W and 3S groups (P = 0.785). A reduction in the number of implants, regardless of the implant diameter, showed higher stress concentration around the implants. Five-implant configuration showed lower stress concentration and seems to be more biomechanically predictable.

Patient-Tailored Cerebral Artery Model for Simulating neurovascular Intervention(3rd Report, Photoelastic Stress Measurement on Vascular Wall Under Simulated Operations)

In this paper, we propose a novel method to product biological models using polyurethane elastomer, which has high photoelastic coefficient and a method to analyze stress states on the model by photoelastic method. With this method, stress condition on vascular wall represented by two principal stresses is clearly visualized on vascular fringe as rainbow-colored photoelastic stress pattern, and the quantitative stress is analyzed from that pattern. For analysis of stress states by photoelastic method, retardation and path length of penetration light through the model must be observed. Proposed method is possible to observe these two parameters simultaneously. Retardation is decided from RGB value of rainbow-colored photoelastic stress pattern and path length is decided from permeability of light. The accuracy of stress analysis is evaluated by tensile test using artery-like cylindrical model. Lastly using the model produced by new method, we analyze stress states quantitatively on the model of cerebral artery. Consequently, it should be valuable for various applications not only surgical simulations but also hemodynamic studies and pathological studies.

Evaluation of photoelastic stress patterns produced by various designs of bilateral distal-extension removable partial dentures

The extent and direction of movement of removable partial dentures during function are influenced by the nature of the supporting structures and the design of the prosthesis. 1 The Academy of Denture Prosthetics: Principles, Concepts, and Practices in Prosthodontics—1967, J. Prosthet. Dent. 19: 180–198, 1968 Google Scholar Since forces are transmitted to abutment teeth by rests, guide planes, and direct retainers during functional movements, optimum design based on the best available research data will preserve the health of abutment teeth and their supporting structures.

Dynamic photoelasticity using TDI imaging

High-speed photographic systems are necessary for recording and visualization of dynamic events in stress analysis, fluid mechanics, etc. Current imaging systems are fairly expensive and generally not simple to use. Furthermore, most are based on photographic film recording systems requiring time consuming and tedious wet processing of the films. Recently, there is lot of interest in developing and modifying CCD architectures and recording arrangements for dynamic scene analysis. Herein we report the use of a CCD camera operating in the time delay and integration mode for digitally recording dynamic photoelastic stress patterns. Applications in strobe and streak photoelastic pattern recording and system limitations will be explained in the paper. In addition, a scheme for dynamic phase shifting using is also explained.

Photoelastic stress pattern analysis using Fourier transform with carrier fringes: influence of quarter-wave plate error

The Fourier transform method, widely applied in photomechanics for the automated analysis of interferometric fringe patterns, has been recently extended to the photoelastic isochromatic fringe patterns analysis. Unfortunately, its use in photoelasticity involves some limitations that have not been completely highlighted in literature. This work deals with the influence of the quarter-wave plate tolerance on the evaluation of the retardation. Both theoretical and experimental analyses have shown that the quarter-wave plate error does not affect the retardation only if the principal stress directions in the model and in the carrier are aligned. In general, instead, the tolerance of the quarter-wave plates leads to an amplification of the retardation error due to the influence of the isoclinics with a subsequent restriction of the field in which the method can be applied. For instance, using common quarter-wave plates and tolerating a maximum retardation error of about 0.03 fringe order, than the Fourier transform method cannot be applied as a full-field technique but only in the model zones in which the misalignment between the principal stresses in the model and in the carrier is less than 15°.

Photoelastic stress patterns produced by implant-retained overdentures

Statement of problem. When 2 implants are used to support a removable overdenture, optimal stress distribution to minimize forces to the implants is desired. Purpose. This study used photoelastic analysis to compare the stress patterns generated around implants with 2 retention mechanisms. Material And Methods. Two root form implants were anchored in a photoelastic mandible and a removable overdenture was fabricated. The denture was lined with a resilient layer of impression material to simulate oral mucosa. Attachment of the denture to the implants was varied by using ball/O-ring and bar-clip attachments. Vertical and oblique occlusal forces from 10 to 200 lb were applied unilaterally to the right and left first molars. Resultant stress distributions in the photoelastic mandible were photographed and evaluated. Results. With vertical forces, the ball/O-ring attachment transferred minimal stress to both implants. Vertical forces applied to the bar-clip overdenture created immediate stress patterns of greater magnitude and concentration on both implants. A posterior oblique load resulted in similar stress patterns to both systems with slightly greater stress to the bar-clip overdenture. Conclusions. Within the limits of this study, ball/O-ring attachments transferred less stress to implants than the bar-clip attachments when the photoelastic model was subjected to a posterior vertical load. (J Prosthet Dent 1998;80:559-64.)

New approaches to the full-field analysis of photoelastic stress patterns

This paper presents two new methods that provide a complete solution for the automatic fringe analysis of photoelastic data. Previous solutions have not yet provided a complete full-field analysis of both fringe sets (isochromatic and isoclinic) over a multiple number of fringes with an automatic measurement of absolute magnitude. This paper reviews previous approaches and discusses the options along which this work has been directed. Specifically, two new algorithms are presented. Firstly, the combination of phase maps at three wavelengths in order to remove the isochromatic ambiguity at every π turning point, that would occur in a single phase map. Additionally, this algorithm allows the automatic measurement of absolute magnitude, providing the neutral axis is within the field of view. Secondly, a new method is proposed that removes the areas of 2π ambiguity in an isoclinic phase map by cross-correlating regions of low modulation at two different wavelengths. The algorithms are demonstrated by applying them to the analysis of an engine connecting rod. The rod was manufactured as a full-scale three-dimensional model in araldite (Ciba-Geigy CT200), from which a central slice was taken after having been stress frozen.

Experimental analysis of a composite automotive suspension arm

In applications where weight saving and parts integration can be achieved, the Rover Group has been investigating the design and manufacture of components from composite materials. The methods used in the different steps in the design-to-manufacture cycle in the high volume automotive industry are relatively well known for a steel component, but are not so well established for a composite component. A design methodology for composites has been emerging in which a principal procedure is design analysis. One of the most established methods of analysis is that using the finite element technique, and this is being supplemented with experimental tests on prototypes using photoelastic analysis and stress pattern analysis by thermal emission, coupled with conventional strain gauge monitoring. Little work has been undertaken to correlate the results obtained from these different test methods and to compare the results with measurements made on an actual component. This paper presents some of the work undertaken concerning the analysis and testing of a composite automotive suspension arm. The results obtained from the three different analysis techniques are compared with experimental test results, and their accuracy is discussed.

Dynamic photoelastic investigation on the mechanics of waterjet and abrasive waterjet machining

An experimental investigation was conducted to study the mechanics of material removal in waterjet and abrasive waterjet (AWJ) piercing processes in a birefringent polymer material. A two-dimensional dynamic photoelasticity experimental set-up was developed and utilized to record the photoelastic stress patterns associated with jet piercing. The fringe patterns recorded by the high-speed camera were used to identify the transient stress fields adjacent to holes pierced. A comparative study of material-removal mechanisms with pure-waterjet and abrasive-waterjet impacting and piercing show that a waterjet contributes to the macrocraking and scooping action of that material, whereas an abrasive waterjet contributes to microcrack nucleation, micromachining, and subsequently erosion.

Evaluation of photoelastic stress patterns produced by various designs of bilateral distal-extension removable partial dentures

The results of this study showed that: 1. The design of a retainer with a mesial rest in conjunction with a buccal I-bar or a wrought-wire and cast lingual arm exhibited the most favorable distribution of vertically applied forces. 2. Retainer designs with a distal rest tend to move the clinical crown distally and the root mesially at the apex, resulting in horizontal forces in the bone. 3. Placing rests of distal-extension removable partial dentures more anteriorly provides an axis of rotation that directs applied forces in a more vertical direction. 4. The distal rest in conjunction with circumferential retainers developed greater horizontal forces within the supporting structures.

Packing and discharge in injection molding

AbstractIn a reciprocating‐screw injection‐molding machine, the screw or plunger forces the plastic into the mold. It remains in the forward position under pressure for a fixed time during which plastic flow into the mold or ‘packing’ takes place. After the timer runs out, the screw moves back while rotating thus releasing the pressure on the plastic in the mold. At this time, if the gate has not frozen, flow of plastic out of the mold or ‘discharge’ takes place. In this study, clear rigid PVC, poly (vinyl chloride), was molded with varying amounts of packing and discharge. Photoelastic stress patterns for parts observed between cross‐polaroids suggested that packing and discharge give rise to high frozen stresses due to molecular orientation in the gate area. Mechanical strength tests on the molded parts show that these high stresses are a source of weakness. Short forward times for the plunger significantly improve the mechanical properties of the parts in the gate area and at the same time have a significant influence on part dimensions, especially in the gate vicinity. Laminations observed at the gate interface can also be reduced by controlling the extent of molecular orientation introduced by packing and discharge.

A stress-optic law for photoelastic analysis of orthotropic composites

The feasibility for utilizing transparent filament-resin composites for photoelastic stress analysis was investigated. Satisfactory photoelastic stress patterns were demonstrated in simple models with undirectional and bidirectional fiber orientations. A stress-optic law was formulated, based on the concept that the birefringence components contributed by each component of plane stress are combined according to a Mohr circle of birefringence. Applying this concept, the difference of the physical and optical principal directions was accounted for, and a general method of photoelastic solution for the plane-stress problem in orthotropic sheets was developed. The method of analysis is little more complex than the well-known procedures for isotropic materials, but at least three experimental measurements are required to characterize the optical response of the material to plane stress. Partial confirmation of the proposed stress-optic law was obtained by comparison of the theory to limited experimental data obtained in uniaxial-stress samples. It remains to establish a more positive verification by experiments in a variety of biaxial-stress conditions.

The Fracture Toughness of Adhesive-Bonded Joints

Abstract Fracture mechanics is related to adhesion theory and the testing of adhesive-bonded joints in the lap-shear configuration. The complexity of the stress field necessitates the strain energy release rate approach, which is followed to derive the relation for a lap-shear sample: Gc = Pc 2/4b (dC/da). Gc is the fracture toughness (critical strain energy release rate), Pc is the breaking or crack instability load, a and b are crack lengths and widths, respectively, and C is the sample compliance for the Tap-shear sample with a crack of these dimensions at each loading edge. It was found that Gc ranged from 1.18 to 1.42 with an average value of 1.34 in.-lb./in.2 for epoxy bonded aluminum strips (EPON 934 and Alcald 2024-T3). Evidence, in the form of photoelastic stress patterns, suggesting that crack extension occurs in the opening mode in lap-shear samples is presented and discussed.

Experimental determination of the elastic-plastic boundary

An experimental method is investigated by which the elastic-plastic boundaries of a rectangular tapered beam having a single concentrated load acting at its free end can be determined. The method, based on the Tresca yield criterion, employs the isochromatics of the photoelastic stress pattern in birefringent coatings and is used to locate experimentally the elastic-plastic boundaries in a series of aluminum beams of small angles of taper. To check these boundary locations theoretically, the simple mechanics-of-materials elastic-plastic beam theory is used, and the comparisons of theoretical and experimental results are shown.

Studies on a Photo-Elastic Method Fixing Stress Patterns at Room Temperature

The usual method of freezing photo-elastic stress patterns is to heat the specimens first and then cool them down very slowly without disturbing the stress patterns obtained at the high temperature. However, if a method which fixes stress patterns at room temperature could be developed, the method would be more useful. For instance, it could be applied to the study of the distribution of stresses in an object placed in a flow, such as a model in a wind tunnel.In this paper, an experiment which fixes stress patterns at room temperature during the curing process of resins was studied.The summary of the experimental results is as follows;(1) The fringe patterns fixed by this method show good coincidence with those obtained by ordinary photo-elastic experiments.(2) The fringe order is proportional to the principal stress difference in an elastic body.(3) The linear relation between the load and the fringe order is retained for a wide range of loads.(4) The fringes are not disturbed by cutting the specimen.Therefore, this method, as well as the heating method, can be used for the three-dimensional analysis of stresses.

Some Recent Developments in Dynamic Photoelasticity

A dual-beam polariscope for obtaining simultaneous normal and oblique incidence photoelastic stress patterns was recently designed for use with a high-speed framing camera. Dynamic stress patterns were photographed at speeds up to 720,000 frames per second using flashtubes and filters to obtain monochromatic light. The equipment and techniques are described and pre-liminary results are given.

A Photoelastic Method for the Study of Cage Strain in a Rolling Element Bearing

A technique has been developed by which interpretable photoelastic stress patterns can be obtained from rolling element bearing cages while operating under conditions of various speed and load. The test specimen utilized in this study was a 130 mm bore cylindrical roller bearing. A layer of bire-fringent plastic was cemented to the outboard side of the cage of the bearing by means of a reflective adhesive. This plastic material was illuminated by means of high intensity polarized light. This light passed through the birefringent plastic material, was reflected by the reflective adhesive and passed back again through the birefringent material and through another polaroid filter (analyzer). A high speed camera was located behind this second polaroid filter. High speed motion pictures were taken of the photoelastic stress patterns produced in the birefringent material as the test bearing was rotated under radial load. Photoelastic stress patterns recorded on the high speed motion picture film were analyzed a...

On the photoelastic examination of vibrating bodies and the photoelastic effect in optically active media

T he interpretation of the photoelastic stress patterns of vibrating bodies is discussed, with particular reference to quartz crystals. An expression is derived for the change in velocity of a light wave propagated along the optic axis due to stresses acting in the plane normal to this axis. Such stresses should cause an increase in the effective rotary power and this is verified by experiment. This result offers an explanation of phenomena observed by earlier workers.

The Fundamentals of an Instantaneous Photography Applied to Photoelasticity

The object of the present paper is to report the fundamentals of an instantaneous photography that an electric spark in a high voltage is used as a light source of photoelastic stress patterns. The electric spark circuit with a subsidiary spark-gap is used in this experiment and the time of exposure of this circuit is set at about 2×1O-6 sec. The best conditions of the exposure and contrast for the Fuji X-ray film are as follows : Deep red filter×2, F=2.8 ; main spark-gap vol. 46-49 K.V.P.P. Deep red filter×1, F=4.0 ; main spark-gap vol. 44-47 K.V.P.P. The main gap distance is set at 22 mm (64.2 K.V.-gap) and a starting voltage of 3 K.V.D.C. is taken in this case. As the examples photographed by this method, stress patterns of the impact of beams and the noched bers are shown. And then the behaviours of plastics under the dynamic stress state are discuseed by the use of Voigt and Maxwell models.