Static Fracture Strength Research Articles

Numerical prediction of dynamic fracture strength of edge-mounted non-symmetric tempered glass panels under steel ball drop impact

Despite the well-known effects of loading rate and specimen size on glass strength, the fracture criterion of products containing tempered glass panels (TGPs) has been established based on the static fracture strength (SFS) of a standard-sized TGP due to procedural difficulties in determining large scale dynamic fracture strength (DFS). This impractical fracture criterion that has universally been adopted in industrial fields results in a use of excessive safety factor in product design and development process. In this work, large scale DFS of full-edge mounted TGPs is numerically predicted using ball drop impact (BDI) simulation, which realize in-service dynamic loading conditions and constraints. The numerical prediction results were verified by a remarkable correlation with a deformation deviation of 1.0–5.0% and stress deviation within about 6.9% comparing to BDI fracture test results. It was found that the average DFS derived in the practical BDI condition was 2.0 times higher than the average SFS derived in standard flexural test condition. We believe this study contributes to setting more efficient fracture criterion when designing or developing products in which TGPs are mounted, with emphasizing difference in glass strength derived from the in-service conditions and the standard test conditions.

August Wöhler – founder of fatigue strength research

AbstractThe year 2014 marked the 100th anniversary of August Wöhler's death. On that occasion the authors wrote a book about his scientific work, his work on the safety of components and structures in the emerging industrial society, his life and his significance for the historical development in the field of fatigue strength of components and structures [1]. Those investigations were accomplished in cooperation with the DVM (German Association for Materials Research and Testing). As national and international events have shown [2], that book is of great interest. Therefore, an English version suggested itself, not least because of the 200th anniversary of Wöhler's birth in 2019.August Wöhler was an interesting and unique character, influenced by the 19th century Industrial Revolution, especially railway development. The spread of that new technology caused numerous problems. Fractures occurred on axles, wheels and rails at stresses below the component's static fracture strength. Through systematic tests, August Wöhler was able to prove that repeated stresses far below the static strength might lead to fractures. The present article gives a brief overview of Wöhler's life and achievements.

Effects of Denture Base Thicknesses and Reinforcement on Fracture Strength in Mandibular Implant Overdenture with Bar Attachment: Under Various Acrylic Resin Types.

Objective This study aimed to assess the effect of reinforcement, denture base thickness, and acrylic resin types on dynamic and static fracture strength in mandibular implant overdentures with bar attachment. Materials and Methods One hundred and eight experimental mandibular implant overdentures with bar attachments were fabricated in three main groups, namely unreinforced (control: C), reinforced with unidirectional glass fibers (FR), and Co–Cr cast metal (MR). Each group included denture bases of 2-, 3-, and 4-mm thicknesses and produced with conventional (CA) and high-impact acrylic (HIA) resins. Specimens were thermocycled (5,000 times, 5–55°C) then subjected to a 400,000 cyclic load regime. Unbroken specimens were then loaded until fracture by a universal testing machine. Differences in mean fracture resistance among the groups were compared using the one-way analysis of variance (with post hoc Tukey's honestly significant difference test) and Student's t -tests (α = 0.05). Results Fracture strength increased significantly when the denture base thickness was increased ( p = 0.001 ) . The 2-mm denture base thickness was not enough for reinforcement. The fracture strength of the FR groups was significantly higher than other groups for 3- and 4-mm thicknesses ( p = 0.001). The fracture strength of the HIA resin was significantly higher than CA resin in FR groups ( p = 0.029 and p = 0.001). MR groups showed the weakest fracture strength. Conclusions The 2-mm denture base thickness had sufficient fracture strength without reinforcement and a positive relationship between acrylic resin thickness and fracture resistance was found.

Influence of testing parameters on the load-bearing capacity of prosthetic materials used for fixed dental prosthesis: A systematic review and meta-analysis

The aim of this study was to systematically review the literature to assess static fracture strength tests applied for FDPs and analyze the impact of periodontal ligament (PDL) simulation on the fracture strength. Original scientific papers published in MEDLINE (PubMed) database between 01/01/1981 and 01/06/2010 were included in this systematic review. Data were analyzed considering the test method (static loading), material type (metal-ceramic-MC, oxide all-ceramic-AC, fiber reinforced composite resin-FRC, composite resin-C), PDL (without or with) and restoration type (single crowns, 3-unit, 4-unit, inlay-retained and cantilever FDPs). The selection process resulted in the 72 studies. In total, 377 subgroups revealed results from static load-bearing capacity of different materials. Fourteen metal-ceramic, 190 AC, 121 FRC, 45 C resin groups were identified as subgroups. Slightly decreased results were observed with the presence of PDL for single crowns (without PDL=1117±215 N; with PDL=876±69 N), 3-unit FDPs (without PDL=791±116 N; with PDL=675±91 N) made of AC, 3-unit FDP (without PDL=1244±270 N; with PDL=930±76 N) and inlay-retained FDP (without PDL=848±104 N; with PDL=820±91 N) made of FRC and 4-unit FDPs (without PDL=548±26 N; with PDL=393±67 N) made of C. Overall, for single crowns, fracture strength of FRC was higher than that of AC and MC; for 3-unit FDPs FRC=C>AC=MC; for 4-unit FDPs AC>FRC>C and for inlay-retained FDPs, FRC=AC. An inclination for decreased static fracture strength could be observed with the simulation of PDL but due to insufficient data this could not be generalized for all materials used for FDPs.

Effect of Cyclic Fatigue Tests on Aging and Their Translational Implications for Survival of All-Ceramic Tooth-Borne Single Crowns and Fixed Dental Prostheses.

The objective of this systematic review was to elaborate the aging effect of cyclic fatigue tests on mechanical durability of all-ceramic single crowns and fixed dental prostheses (FDP). Original scientific papers published in the MEDLINE (PubMed) database in English between 01/01/1950 and 12/31/2013 on cyclic loading on all-ceramics were included in this systematic review. The following MeSH terms, search terms, and their combinations were used: "in vitro," "stress mechanical," "crowns," "denture, partial, fixed," "dentistry," "fatigue," "all-ceramic," "zirconia," "fixed dental prosthesis," "FDP," "bridges," and "cyclic loading." Two reviewers performed screening and analyzed the data. Only the studies that reported on both static fracture strength and static fracture after fatigue of all-ceramic single crowns and FDPs that allowed comparison of aging effect through cyclic loading were included. The selection process resulted in a final sample of 14 journal articles. In total, 9 articles were identified related to all-ceramic single crowns, 3 of which were on anterior and 6 on posterior crowns, and 5 articles on 3-unit FDPs, all of which were on posterior FDPs. Fatigue cycles varied between minimum of 1000 to maximum 1,200,000 cycles for crowns and 10,000 to 2,000,000 cycles for 3-unit FDPs. The applied force during cyclic loading varied between 20 to 300 N for single crowns and 49 to 200 N for 3-unit FDPs. For the 3-unit FDPs, fracture strength results showed slightly decreased values after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (841 ± 244 to 2434 ± 154 N). For crowns similar trends were not observed, but cyclic loading decreased the fracture strength in only some materials after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (395 ± 96 to 2726 N). An inclination for decreased static fracture strength could be observed after cyclic loading of all-ceramic single crowns and FDPs, but this was material specific. Due to the heterogeneity of data such as aging, loading conditions, and fewer experimental groups, statistical analysis could not be performed. Cyclic loading tests require more standardized guidelines for testing and reporting.

Enhanced large-scale analysis method and its application to multiaxial pipe weld

A large-scale infrared ray telescope is to be built as a next-generation telescope. In this telescope, a large reflector is supported by a truss structure and welded joints that consist of multiple pipes. This paper investigates welding residual stress, which affects fatigue strength and static fracture strength. In the investigation, a novel large-scale analysis method for welding mechanics was developed based on an idealized explicit finite element method (FEM) using the multigrid method. To show the capability of the developed method, it was applied to a fundamental bead-on-plate problem. Residual stress distribution on a multiaxial pipe was studied by using the developed method. The analysis and measurement were compared to show the accuracy of the analysis, and the results showed that the shrinkage of each pipe and residual stress distribution were in good agreement. It was also found that subsequent welding may affect residual stress distribution if the parts being welded are close to each other and that the effect of subsequent welding is small if they are separated. The analysis was finished within almost 10 days. Therefore, the developed multigrid idealized explicit FEM can analyze the welding residual stress of complex structures in a realistic computing time.

802 薄層平織CFRP積層板の切欠強度のプライスケールおよびサブラミネートスケール依存性(OS8-(1),OS8 オーガナイズドセッション≪複合材料の変形と破壊およびマルチスケール計算技術≫)

Size effect on the static tensile fracture strength of thin-ply woven carbon fiber composite laminates as well as its stacking sequence dependence is studied. Applicability of existing strength models to the notch size and scale dependent tensile fracture strength is also examined. Two kinds of woven fabric composites ([(0/90)_n/(±45)_n]_s and [(0/90)/(±45)]_<ms>) are tested. To observe the effect of specimen size, static tension tests are performed on 1D, 2D and 3D-geometrically similar specimens. Unnotched (UN) and double-edge notched (DEN) were prepared for each size, respectively. To elucidate the size effect on notch sensitivity, furthermore, 1D, 2D and 3D scaled DEN specimens are tested for different notch lengths, respectively. It is observed that the tensile fracture strength of DEN specimens significantly decreases as the size of specimen increases. As the specimen size decreases, the tensile fracture behavior gradually shifts from a LEFM-dominated region to an UN-strength-dominated region.

Hydrogen enhanced mechanical fatigue in single crystal silicon

Silicon fatigue lifetime was examined in four different environments. Fatigue failure occurs in the range of 103–105 cycles under the stress amplitude level of around 90% to the static fracture strength under monotonic loading, both in lab air with relative humidity (RH) 35–40% and hydrogen with RH 5%. In contrast, no specimen fractures with the same stress level up to more than 107 cycles in nitrogen and oxygen with RH 5%. These facts suggest that hydrogen, which could also be supplied from water adsorbed on the surface, had a significant impact on the fatigue damage accumulation in silicon.

A prediction scheme of the static fracture strength of MEMS structures based on the characterization of damage distribution on a processed surface

This paper presents a scheme for predicting the strength of MEMS structures patterned into arbitrary shapes by deep reactive ion etching of a silicon wafer. The scheme is based on the inhomogeneous defect distribution on the etched surfaces. Single-crystal silicon specimens with different shapes were subjected to four-point bending tests with monotonically increasing load. The distributions of the fracture strength were described using two-parameter Weibull statistics, where the two parameters are defined as functions of the etching depth representing the inhomogeneity of the damage on the etched surface in the direction perpendicular to the wafer. In order to estimate the distribution of the local strength determined by the local level of damage, the etched surfaces of specimens without a notch were tested in three different bending directions corresponding to three different stress distributions, and three different strength levels were given due to surface roughness conditions caused by the non-uniformity of the etching process. The estimated values of the parameters were used to estimate the fracture strength of four types of notched specimens with different notch tip radii. The results of comparison between the distributions of predicted strengths and experimental data showed that the fracture strength of arbitrarily shaped structures is predictable on the basis of the information obtained from specimens without notch, by taking into account the characteristics of etched surface, i.e. the inhomogeneous damage.

J211012 繰り返し圧縮応力によるシリコン単結晶中の欠陥形成と残存引張強度([J211-01]"壊れない"マイクロシステムのためのナノ力学・ナノ計測(1))

In this study, we investigated the possible correlation between fatigue mechanism and internal defects such as dislocation through the fatigue test under cyclic compressive loading. We used specimens made of p-type single crystalline silicon wafer, and prepared with p-n junction and ohmic contact in advance to the fatigue test. The specimen having oval trench was designed for approximately 2.27GPa compressive stress concentration. The fatigue test with a frequency of 20 Hz and range from 1×10^6 to 1×10^7 cycles was performed under controlled atmospheres (80℃, 80% relative humidity). By detecting electron beam induced current (EBIC), growth of internal defects was observed in a scanning electron microscope. After the fatigue test, static fracture strength was reduced by approximately 16% due to the defects induced by cyclic compressive stress. This is likely to be a mechanism determining fatigue lifetime of silicon, as well as a risk to fatigue fracture.

Low-Cycle to Ultrahigh-Cycle Fatigue Lifetime Measurement of Single-Crystal-Silicon Specimens Using a Microresonator Test Device

The authors used a ramping-amplitude fatigue-test method to perform low-cycle fatigue tests in micrometer-sized single-crystal-silicon specimens using a resonant-type fatigue-test device. Very short delayed fractures from 4 ms to 29 s were observed by controlling the amplitude ramping rates with two self-oscillation electric circuits and different parameters. These lifetimes were converted to corresponding constant-amplitude lifetimes from 101 to 105 cycles using the relationship derived from a crack-growth analysis. S-N plots of measured lifetimes exhibited the transition of fatigue lives at the high-cycle region with a crack-growth exponent of 18.0, to the static fracture strength of 6.50 GPa at the low-cycle region corresponding to the original crack length of 7.9 nm. The existence of a very rapid fatigue fracture within 1 s was confirmed. From the obtained crack-growth parameters, the evolution of crack length and the effects of humidity were discussed.

Preparation and characterization of ZTA bioceramics with and without gradient in composition

Properties and proof of suitability of homogeneously and graded ZTA bioceramics with various Y 2 O 3 stabilized zirconia contents were investigated. Therefore porous alumina was infiltrated with different amounts of Y 2 O 3 doped ZrO 2 precursors. At homogeneously infiltrated samples biaxial flexural strength and wear behavior were investigated (ISO 6474). Subsequently, at hip joint heads the static fracture strength was determined (ISO 7206-10). Materials ranging from approx. 4 to 20 wt% Y 2 O 3 stabilized zirconia were characterized relative to the sinter density, the microstructure, the phase composition and the dispersion of the stabilized zirconia phase. Bioceramics showed high sinter density, fine microstructures, excellent wear property and significantly increased biaxial flexural strength. A 41% increase in strength through the formation of Y 2 O 3 stabilized zirconia gradient in the conical bore of the heads was reached. Low compressive stresses in cone of this heads were found. ZTA bioceramics are potentially suitable for use as hip replacement components.

Prediction of the static fracture strength of hole notched plain weave CFRP composites

This study aims to investigate the effect of hole-notch size and the specimen width on the notched strength of woven carbon fiber reinforced plastic (CFRP) composites. It is found that a notch sensitivity coefficient can be modeled as a function of the specimen geometry and the mechanical properties. From the experimental results, the values of σ N ∞ / σ u can be represented only as a function of d o / R. Subsequently, a predictive model for the fracture strength of hole-notched specimens is proposed.

Fatigue strength of a paper-based friction material under shear–compressive loading

This paper deals with the fatigue strength of a paper-based friction material under the cyclic shear-compressive loading which is regarded as a real loading condition in an automotive automatic transmission. The paper-based friction material are composed of aramid fibers and phenolic resin. Static fracture and fatigue tests are carried out under various shear and compressive stress conditions. The S-N curves of the paper-based friction material under shear-compressive stresses are described by straight lines in a log-log diagram. The static fracture strength and fatigue strength are higher when the compressive stress is more dominant. The pure compressive cyclic deformation tests are also carried out to explain the fatigue strength of the paper-based friction material under compressive-dominant stress condition. From the tests, it is made clear that with increasing compressive stress, the friction materials becomes dense and the Young's modulus or slope of cyclic stress-strain relation becomes high, and as a result the strain range of the cyclic stress-strain relation remains as constant low value. Therefore, it is considered that the fatigue strength of the paper-based friction material is remarkably high under the compressive-dominant stress condition.

Strength Evaluation of Alumina Spray Coating (2nd Report, Proposal for Judgment of Crack Interference and Correction Methods of Crack- Shape)

The alumina spray coating is a material containing many pores (cracks) and there is a crack-interference in the alumina spray coating, therefore, the crack-interference leads to a decrease in the fracture strength. There are some studies that have used the elastic analysis for two or more cracks. Moreover, there are some standards for the combining of the cracks. However, in ceramics including alumina, a study of quantifying the internal spread of the crack when interfering and presuming a static fracture strength with judgment of the crack-interference after the stable crack propagation is not known. In this study, after the alumina spray coating single layer was taken out, a Vickers' indentation crack was introduced, a 4-point bending test was performed and a R-curve was acquired. As a result, the fracture strength characteristic of the alumina spray coating single layer was clarified. Three judgments of the crack-interference with the R-curve were then proposed. Moreover, a correction method of the crack-shape when the cracks interfere was proposed. The validities of the proposals were verified with bending tests after two Vickers' indentation cracks were introduced.

T0101-1-4 摩擦紙の引張および圧縮-せん断負荷下における疲労強度評価([T0101-1]マイクロ・ナノ材料システムの力学と強度・機能評価(1):ナノインプリント・シートの力学特性評価)

This paper deals with the fatigue strength the paper-based friction materials under cyclic shear-compressive loading which is regarded as a real loading condition in an automotive automatic transmission. The influence of ratios between the shear and compressive stress on the fatigue strength was examined. The fatigue strength decreases with increasing number of cycles. The static fracture strength and fatigue limit is high under the dominant compressive stress condition. The amount of deformation of the paper-based friction materials does not change with the compressive stress under the compressive loading, while the Young's moduli increase with increasing compressive stress.

A study of prediction of static fracture strength of MEMS structure for strength design scheme

Aiming at development of evaluation scheme for strength design and reliability of MEMS structure, this paper proposes prediction method of static fracture strength of specimens patterned by Bosch process. Two types of specimens made of single crystal silicon with different stress distributions were prepared for measuring the fracture strength. Four-point bending test in different loading directions was carried out to consider distribution of the state of damage due to machining. Relationship between cumulative fracture probability and applied stress was investigated by applying Weibull statistics and performing finite element method (FEM) simulation. It demonstrated the possibility of quantitative prediction for the fracture strength of specimens with arbitrary shapes.

OS0509 摩擦紙の圧縮-せん断疲労強度評価に関する研究(微視構造を有する材料の変形と破壊,オーガナイズドセッション)

Paper-based friction materials have been used for power train in vehicles. The motional property and reliability of vehicles depend on mechanical properties and strength of the paper-based friction materials. The paper-based friction materials consist of aramid fibers, cellulose fibers, carbon fibers, fillers and resin, and have an extremely complex microstructure. Test methods to evaluate the mechanical properties and strength of paper-based friction materials have not been established, and therefore their mechanical properties and strength are not fully investigated. In this study, test methods to evaluate the static fracture strength and fatigue strength under combined load of compression and shear were developed. Static fracture tests and fatigue tests were carried out on a aramid fiber based friction paper, and influence of an stress ratio of shear to compression on the static and fatigue strengths was discussed.

163 CFRP積層板接着継手の静的破壊強度と破壊形態に関する研究(GS1-3 先端材料の強度評価)

163 CFRP積層板接着継手の静的破壊強度と破壊形態に関する研究(GS1-3 先端材料の強度評価)

Applicability of crack energy density to fracture strength evaluation of piezoelectric ceramics

A lot of studies have been made to grasp and describe fracture behavior of piezoelectric material under electromechanical loadings. However, even the criterion to describe the dependence of static fracture strength on electric field has not been established yet. In this paper, a fracture criterion based on mechanical contribution of crack energy density is proposed and its applicability is studied by analyzing not only the three-point bending fracture test results by the authors on piezoelectric ceramics called C-2 but also the compact tension fracture tests by Park and Sun on piezoelectric ceramics called PZT-4, based on the criterion.