| 1. |
- Kumar, Uday, et al.
(author)
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Reliability investigation for a fleet of load haul dump machines in a Swedish mine
- 1989
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In: Reliability Engineering & System Safety. - : Elsevier BV. - 0951-8320 .- 1879-0836. ; 26:4, s. 341-361
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Journal article (peer-reviewed)abstract
- The recent trends of deployment of complex and capital intensive equipment in mines has created interest in the field of maintenance and operational reliability of this equipment. The failure consequences associated with random equipment failures have considerable influence on the total operating cost of a highly mechanized mining system. Keeping this in view, a reliability investigation was initiated for a fleet of diesel operated load-haul-dump (LHD) machines in a Swedish mine. The goal is to estimate the operational reliability of these machines, locate items or assemblies which need improvement in design to enhance the reliability and to decide the duration of optimal preventive maintenance. Failure data for one year of LHD machines are analysed using the recently developed graphical technique of total time on test (TTT) plotting. Analytical methods like Kolmogorov-Smirnov test and maximum likelihood estimation are used in the analysis. The importance of testing the reliability data for the presence of trends and serial correlation is also emphasized.
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| 2. |
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| 3. |
- Basu, A.P, et al.
(author)
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Multivariate harmonic new better than used in expectation distributions
- 1983
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In: Scandinavian Journal of Statistics. - 0303-6898 .- 1467-9469. ; 10:1, s. 19-25
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Journal article (peer-reviewed)abstract
- Various definitions of multivariate harmonic new better than used in expectation (MHNBUE) life distributions are introduced and their interrelationships are studied. The definitions are multivariate generalizations of the univariate aging property HNBUE which is weaker than the new better than used in expectation (NBUE) property. Various closure properties of the different MHNBUE classes are proved. Some examples are also given to illustrate the relationships between our MHNBUE properties and the MNBUE properties presented by Buchanan and Singpurwalla (1977). We also study the dual multivariate harmonic new worse than used in expectation (MHNWUE) classes
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| 4. |
- Bergman, Bo, et al.
(author)
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A family of test statistics for detecting monotone mean residual life
- 1989
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In: Journal of Statistical Planning and Inference. - : Elsevier BV. - 0378-3758 .- 1873-1171. ; 21:2, s. 161-178
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Journal article (peer-reviewed)abstract
- The mean residual life of a life distribution F with survival function F̄=1-F is defined as e(x)=(sh{phonetic}∞xF̄(t)dt)/F̄(x) if F̄(x)>0 (e(x)=0 if F̄(x)=0). The function e(x) has proved to be of great interest in many different areas such as biometry, reliability and social sciences. The class DMRL (IMRL) consists of those life distributions which have decreasing (increasing) mean residual life; i.e. e(x) is a decreasing (increasing) function of x. In this paper we present and study a family of test statistics intended for testing exponentiality against DMRL (IMRL). The family includes the test statistics proposed for the same purpose by Hollander and Proschan (1975) for complete samples and later generalized by Chen et al. (1983a) to accomodate randomly right censored samples. We compare the efficiency for different members in the family of test statistics when testing against some different alternatives. Furthermore, we study the efficiency loss due to different amount of exponential censoring. The asymptotical normal distribution of the test statistics are presented and the quality of the normal approximation is also discussed
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| 5. |
- Bergman, Bo, et al.
(author)
-
A graphical method applicable to age-replacement problems
- 1982
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In: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; R-31:5, s. 478-481
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Journal article (peer-reviewed)abstract
- The Total Time on Test (TTT) concept has proven to be a very useful tool in several reliability contexts. The objective of this note is to illustrate how a generalization of the TTT-concept, the TTT-transform, defined as a certain function of the survivor function, can be used when analyzing different types of age-replacement problems. (14 refs.)
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| 6. |
- Bergman, Bo, et al.
(author)
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A note on some test statistics against HNBUE
- 1987
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In: Annals of the Institute of Statistical Mathematics. - 0020-3157 .- 1572-9052. ; 39:3, s. 483-488
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Journal article (peer-reviewed)abstract
- Some comments and extensions are given to the paper on statistics for testing exponentiality against the HNBUEE property (i.e. {Mathematical expression} ≦μ exp(-t/μ), t≧0) by Basu and Ebrahimi
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| 7. |
- Bergman, Bo, et al.
(author)
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Letter to the editors
- 1988
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In: Reliability Engineering & System Safety. - : Elsevier BV. - 0951-8320 .- 1879-0836. ; 21:2, s. 155-160
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Journal article (other academic/artistic)
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| 8. |
- Bergman, Bo, et al.
(author)
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Testing against HNBUE with randomly censored data
- 1985
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In: Contributions to probability and statistics in honour of Gunnar Blom. - Lund : Lund University. Department of Mathematical Statistics. ; , s. 49-72
-
Book chapter (other academic/artistic)abstract
- The "harmonic new better than used in expectation" (HNBUE) class of life distributions contains all the more familiar classes from reliability theory such as the "increasing failure rate" (IFR) and "new better than used" (NBU), while still allowing one to formulate interesting inequalities comparing such distributions with the memoryless exponential distribution. In this paper test statistics based on the product-limit estimator are derived for testing the hypothesis of HNBUE versus exponentiality given a sample of censored observations from the life distribution of interest. A study of the asymptotic relative efficiency focusses on the loss of information due to censoring.
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| 9. |
- Bergman, Bo, et al.
(author)
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The total time on test concept and its use in reliability theory
- 1984
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In: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 32:3, s. 596-606
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Journal article (peer-reviewed)abstract
- More than 30 years ago, Epstein and Sobel introduced the Total Time on Test (TTT-) concept. During the last 10 years different generalizations of this concept have been defined and studied, e.g. the TTT-transform and the TTT-plot; a basic paper was presented by Barlow and Campo in 1975. Many of these generalizations have proven to be very useful in different areas of reliability, both from a theoretical and a practical point of view. The purpose of this expository paper is to present some of these generalizations and illustrate their value.
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| 10. |
- Bergman, Bo, et al.
(author)
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TTT-concept and replacements to extend system life
- 1987
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In: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 28:3, s. 302-307
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Journal article (peer-reviewed)abstract
- In a number of papers the current authors have illustrated how the Total Time on Test (TTT) concept can be used when analysing the ordinary age replacement problem and different generalization thereof. In this paper we show that the TTT-concept is very useful also when analysing another replacement problem discussed by C. Derman et al. in which the replacements of a vital component, for which there are n space units, are made with the goal of maximizing the expected system life. (12 refs.)
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| 11. |
- Bergman, Bo, et al.
(author)
-
TTT transforms and age replacements with discounted costs
- 1983
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In: Naval Research Logistics Quarterly. - : Wiley. - 0028-1441 .- 1931-9193. ; 30:4, s. 631-639
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Journal article (peer-reviewed)abstract
- The ordinary age replacement problem consists of finding an optimal age at which a unit, needed in a continuous production process, should be replaced in order to minimize the average long-run cost per unit time. Bergman introduced a graphical procedure based on the total-time-on-test (TTT) concept for the analysis of the age replacement problem. In this article, that idea is generalized to the situation of discounted costs. We also study a more general age replacement problem in which we have a form of imperfect repair.
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| 12. |
- Klefsjö, Bengt
(author)
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A useful ageing property based on the Laplace transform
- 1983
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In: Journal of Applied Probability. - : Cambridge University Press (CUP). - 0021-9002 .- 1475-6072. ; 20:3, s. 615-626
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Journal article (peer-reviewed)abstract
- The class of life distributions for which , where , and , is studied. We prove that this class is larger than the HNBUE (HNWUE) class (consisting of those life distributions for which for x ≧ 0) and present results concerning closure properties under some usual reliability operations. We also study some shock models and a certain cumulative damage model. The class of discrete life distributions for which for 0 ≦ p ≦ 1, where , is also studied.
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| 13. |
- Klefsjö, Bengt
(author)
-
HNBUE survival under some shock models
- 1981
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In: Scandinavian Journal of Statistics. - 0303-6898 .- 1467-9469. ; 8:1, s. 39-47
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Journal article (peer-reviewed)abstract
- Suppose that a device is subjected to shocks governed by a counting process N={N(t):t⩾O}. The probability that the device survives beyond t is then H¯(t)=Σk=O∞P(N(t)=k)P¯k, where P¯k is the probability of surviving k shocks. In this paper the author proves that H¯(t) is HNBUE (HNWUE), i.e. ∫t∞H¯(x)dx⩽(⩾)μexp(-t/ν) for t⩾O, where μ=∫O∞H¯(x)dx, under some different conditions on N and (P¯k)k=O∞. For instance the author studies the case when the inter-arrival times between the shocks are dependent and HNBUE (HNWUE). This situation includes the cases when N is a Poisson process or a birth process. Further a certain cumulative damage model is studied (14 refs.)
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| 14. |
- Klefsjö, Bengt
(author)
-
NBU and NBUE survival under the Marshall-Olkin shock model
- 1982
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In: I A P Q R Transactions. - 0970-0102. ; 7:2, s. 87-96
-
Journal article (peer-reviewed)abstract
- Engineering or biological systems consisting of two components, each with its own lifetime, are studied. The joint probability distribution of lifetimes is modelled by supposing that the components of the system are subjected to a single Poisson stream of shocks. Either component can fail at the time of a shock when its cumulative damage becomes sufficiently large. This is formalized by specifying the probability that each device survives any number of shocks. It is shown how aging properties of the discrete bivariate distribution of number of shocks survived carry over to aging properties of the bivariate lifetime distribution.
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| 15. |
- Klefsjö, Bengt
(author)
-
On aging properties and total time on test transforms
- 1982
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In: Scandinavian Journal of Statistics. - 0303-6898 .- 1467-9469. ; 9:1, s. 37-41
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Journal article (peer-reviewed)abstract
- Barlow and Campo (1975) presented the Total Time of Test (TTT-)transform as a tool for identification of failure distribution models. Since then the TTT-transform has proved to be useful also in several other connections. Recently Barlow (1979) discussed relationships between the TTT-transform and the aging properties IFR and IFRA. The author note presents some relationships between the TTT-transform and other aging properties, e.g. DMRI, HNBUE and heavy-tailedness (17 refs.)
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| 16. |
- Klefsjö, Bengt
(author)
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On closure under formation of parallell systems
- 1984
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In: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; R-33:5, s. 423-
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Journal article (peer-reviewed)abstract
- It is shown that a parallel system of s-independent identical components has the same aging property (for example, increasing failure rate or increasing average failure rate) as the components (6 refs.)
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| 17. |
- Klefsjö, Bengt
(author)
-
Reliability interpretations of some concepts from economics
- 1984
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In: Naval Research Logistics Quarterly. - : Wiley. - 0028-1441 .- 1931-9193. ; 31:2, s. 301-308
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Journal article (peer-reviewed)abstract
- In a recent article, M. Chandra and N. D. Singpurwalla have pointed out the close relationship between the Lorenz curve, which is frequently used when illustrating income distributions in economics, and the total-time-on-test transform, which has proved to be a very useful tool in reliability. They also presented some characterizations of aging properties by using the Lorenz curve. The purpose of this article is to point out some further results in the same area and to give reliability interpretations of some common measures of income inequality. (21 refs.)
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| 18. |
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| 19. |
- Klefsjö, Bengt
(author)
-
Some comments on a paper on k-HNBUE life distributions
- 1985
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In: Annals of the Institute of Statistical Mathematics. - 0020-3157 .- 1572-9052. ; 37:1, s. 361-364
-
Journal article (peer-reviewed)abstract
- In a recent paper by A. P. Basu and N. Ebrahimi (1984, Ann. Inst. Statist. Math., A, 36, 87-100) a new class of life distributions calledk-HNBUE (with dualk-HNWUE) is introduced. Closure properties and bounds on the moments and on the survival function to ak-HNBUE (k-HNWUE) life distribution are presented. However, some of the results presented are incorrect.
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| 20. |
- Klefsjö, Bengt
(author)
-
Some tests against aging based on the total time on test transform
- 1983
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In: Communications in Statistics - Theory and Methods. - : Informa UK Limited. - 0361-0926 .- 1532-415X. ; 12:8, s. 907-927
-
Journal article (peer-reviewed)abstract
- Let F be a life distribution with survival function = 1 - F and finite mean The scaled total time on test transform was introduced by Barlow and Campo (1975) as a tool in the statistical analysis of life data. The aging properties IFR, IFRA, NBUE and DMRL can be translated to properties of ϕF(t). Guided by these properties of ϕF(t) we suggest some test statistics for testing exponentiality against IFR, IFRA, NBUE and DMRL, respectively. The IFR and IFRA tests are new; the NBUE and DMRL tests have already been proposed and stu- died by Hollander and Proschan (1975) . The exact and asymptotic distributions of the statistics are derived and the asymptotic efficiencies of the tests are studied. The power of some tests is estimated by simulation for some alternatives when the sample size is n = 10 or n = 20.
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| 21. |
- Klefsjö, Bengt
(author)
-
Survival under the pure birth shock model
- 1981
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In: Journal of Applied Probability. - : Cambridge University Press (CUP). - 0021-9002 .- 1475-6072. ; 18:2, s. 554-560
-
Journal article (peer-reviewed)abstract
- Suppose that a device is subjected to shocks and that P sub(k), k = 0, 1, 2,..., denotes the probability of surviving k shocks. Then H(t) = Sigma super( infinity )@)dk sub(=) sub(0) P(N(t)=k)P sub(k) is the probability that the device will survive beyond t, where N = (N(t):t greater than or equal to 0) is the counting process which governs the arrival of shocks. A-Hameed and Proschan (1975) considered the survival function H(t) under what they called the pure birth shock model. In this paper we shall prove that H(t) is IFRA and DMRL under conditions which differ from those used by A-Hameed and Proschan (1975).
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| 22. |
- Klefsjö, Bengt
(author)
-
Testing against a change in the NBUE property
- 1989
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In: Microelectronics and reliability. - : Elsevier BV. - 0026-2714 .- 1872-941X. ; 29:4, s. 559-570
-
Journal article (peer-reviewed)abstract
- A life distribution F with survival function F=1-F, finite mean μ and mean residual life e(t) is said to be NBUE (NWUE) if e(t)⩽(⩾)μ for t⩾0. This NBUE (NWUE) property can equivalently be characterized by the fact that φ(u)⩽(⩾)u for 0⩽u⩽1, where φ(u) is the scaled TTT-transform of F. A generalization of the NBUE and NWUE properties is that there is a value of s such that φ(u)⩾u for 0⩽u⩽p and φ(u)⩽u for p⩽u⩽1, or vice versa. This means a trend change in the NBUE property. This generalized aging property is called the NBUE-NWUE property. In this paper the authors present and study a test statistic intended for testing exponentiality (i.e. φ(u)=u for 0⩽u⩽1) against this NBUE-NWUE property. The asymptotic normality of the test statistic, suitably normalized, is established and a simulation study is presented (20 refs.)
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| 23. |
- Klefsjö, Bengt
(author)
-
Testing exponentiality against HNBUE
- 1983
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In: Scandinavian Journal of Statistics. - 0303-6898 .- 1467-9469. ; 10:2, s. 65-75
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Journal article (peer-reviewed)
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| 24. |
- Klefsjö, Bengt
(author)
-
The HNBUE and HNWUE classes of life distributions
- 1982
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In: Naval Research Logistics Quarterly. - : Wiley. - 0028-1441 .- 1931-9193. ; 29:2, s. 331-345
-
Journal article (peer-reviewed)abstract
- Different properties of the HNBUE (HNWUE) class of life distributions are presented. The author characterizes the HNBUE (HNWUE) property by using the Laplace transform and presents some bounds on the survival function of a HNBUE (HNWUE) life distribution. He also examines whether the HNBUE (HNWUE) property is preserved under the reliability operations: formation of coherent structure; convolution; and mixture. The class of distributions with the discrete HNBUE (discrete HNWUE) property is also studied (17 refs.)
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| 25. |
- Klefsjö, Bengt
(author)
-
TTT-transforms : a usefulL tool when analysing different reliability problems
- 1986
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In: Reliability Engineering (1980-1987). - : Elsevier BV. - 0143-8174. ; 15:3, s. 231-241
-
Journal article (peer-reviewed)abstract
- During the last ten years different generalizations of the total time on test (TTT) concept have been defined and studied. Among these are a certain functional of the survival function, called the TTT-transform, and an empirical counterpart, called the TTT-plot. These concepts have proved to be useful in many different applications in reliability. The purpose of this paper is to mention some of these applications.
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| 26. |
- Fritzson, Dag
(author)
-
On the Design and Life Prediction of Transmission Belts Made of Elastomer Composites
- 1988
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Doctoral thesis (other academic/artistic)abstract
- Next to gear transmissions, belt transmissions are the most important mechanical transmissions. Today, belt design and development is based on extensive application tests of belts in the product development process. There is a need for theory development and design support systems. This would enable simulation for prediction and optimization of fatigue life. The aim of this work is to study certain parts of the belt in detail when the belt is running under loaded conditions. The areas of special interest are those which can be related to failure mechanisms. Thus the model can be used for calculations to predict service life. Here, the attention is focused on V-belts. A fully three-dimensional finite strain constitutive model has been developed for the anisotropic elastomer composites used in V-belts and the constitutive model has been implemented into FEM-software. This makes it possible to do general stress and strain analysis of machine elements designed of elastomer composites. Several different failure modes can be identified in V-belt fatigue. Here it is shown that the failure modes thus defined occur for such test conditions that long life can be associated with radial cracks, medium life with separation, and cord break with short life. In order to monitor the stress-strain state at any location in the belt, while simulating a running belt, “the parametric belt segment model” has been developed. Correlation with V-belt fatigue data for 11 different load cases has been made. Our conclusion is that both failure mode and fatigue life can be predicted using computer simulations. Friction and wear of materials in a V-belt drive have also been studied.
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| 27. |
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| 28. |
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