On the accuracy of nominal, structural, and local stress based approaches in designing aluminium welded joints against fatigue

Zamzami, I. Al; Susmel, Luca

doi:10.1016/j.ijfatigue.2016.11.002

Cited by 42 publications

(21 citation statements)

References 41 publications

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“…As done for the previous statistical re-analyses, the scatter band shown in Fig. 10 (which is delimited by two straight lines that are characterised by a probability of survival, PS, equal to 90% and 10%, respectively) was estimated under the hypothesis of a lognormal distribution of the number of cycles to failure for each stress level, with the confidence level being taken equal to 95% [19,20].…”

Section: Unifying Design Curvementioning

confidence: 99%

“…In these charts, for any experimental result, the amplitude of the applied stress, a, is plotted against the resulting number of cycles to failure, Nf (on logarithmic scales). The associated scatter bands were calculated, for a probability of survival, PS, equal to 90% and 10%, under the hypothesis of a log-normal distribution of the number of cycles to failure for each stress amplitude, with this being done by setting the confidence level invariably equal to 95%[19,20]. It is important to point out here that this rigorous statistical procedure was used not only to build the SN diagrams reported in Figures 3 to 5, but also those shown/summarised inFigures 6 to 10.…”

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confidence: 99%

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Fatigue strength of additively manufactured polylactide (PLA): effect of raster angle and non-zero mean stresses

Ezeh

Susmel

2019

International Journal of Fatigue

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As far as polymers are concerned, polylactide (PLA) is certainly the polymeric compound that is most commonly used along with commercial additive manufacturing technologies. In this context, the present paper aims to investigate the influence of manufacturing direction and superimposed static stresses on the fatigue strength of PLA 3D-printed by using the Fused Filament Fabrication technique. This was done not only by generating a large number of new experimental results, but also by re-analysing different data sets taken from the technical literature. As long as the fused deposition modelling technology is used to fabricate, flat on the build-plate, objects of PLA, the obtained results and the performed re-analyses allowed us to come to the following conclusions: (i) the influence of the manufacturing direction can be neglected with little loss of accuracy; (ii) the effect of superimposed static stresses can be quantified and assessed effectively by simply performing the fatigue assessment in terms of maximum stress in the cycle; (iii) if appropriate experiments cannot be run, AM PLA can be designed against fatigue (for a probability of survival larger than 90%) by referring to a unifying design curve having negative inverse slope equal to 5.5 and endurance limit (at =2•10 6 cycles to failure) equal to 10% of the material ultimate tensile strength.

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Section: Unifying Design Curvementioning

confidence: 99%

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confidence: 99%

Fatigue strength of additively manufactured polylactide (PLA): effect of raster angle and non-zero mean stresses

Ezeh

Susmel

2019

International Journal of Fatigue

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“…The scatter band of Figure (determined by referring to a probability of survival, P S , equal to 99% and 1%) was calculated by post‐processing the experimental results under the hypothesis of a log‐normal distribution of the number of cycles to failure for each stress level, with the confidence level being taken equal to 95% . In Figure , the results from the statistical analysis are reported in terms of negative inverse slope, k , endurance limit, σ MAX,99% , at N Ref = 2·10 6 cycles to failure for P S = 99%, and, finally, scatter ratio, T σ , of the endurance limit for P S = 90% and P S = 10%.…”

Section: Fatigue Strength Of Am Plamentioning

confidence: 99%

Reference strength values to design against static and fatigue loading polylactide additively manufactured with in‐fill level equal to 100%

Ezeh

Susmel

2019

Mat Design & Process Comms

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The aim of this paper is to provide a quantitative examination of the state-of-theart knowledge of the static and fatigue behaviour of additively manufactured (AM) polylactide (PLA). To this end, existing literature was reviewed, and a number of data sets were extracted and re-analysed in terms of static strength and standard S-N curves. As long as objects are 3D-printed flat on the build plate, printing direction appears to have little effect on the mechanical behaviour of AM PLA, therefore stress/strain analysis can be performed effectively by simply treating this polymer as a linear-elastic, homogenous, and isotropic material. If static strength cannot be determined experimentally, a conservative reference value of 22 MPa is suggested as being used in situations of practical interest. As far as fatigue is concerned, findings from post-processing reveal that non-zero mean stresses can be modelled by simply using the maximum stress in the cycle. According to the statistical re-analysis discussed in the paper, a reference fatigue curve for the design of AM PLA subjected to uniaxial cyclic loading (for a probability of survival larger than 90%) can be defined by taking the negative inverse slope equal to 5.5 and the endurance limit (at 2·10 6 cycles to failure) equal to 10% of the material ultimate tensile strength.KEYWORDS additive manufacturing, polylactide (PLA), static assessment, fatigue assessment 1 | INTRODUCTION Additive manufacturing (AM) can be described as a collection of technologies that build three-dimensional (3D) objects by systematically adding layer-upon-layer of material. Once a virtual model is produced using a 3D-modelling software, the AM machine reads the data from the file and lays down successive layers of materials to create the 3D solid. This technology facilitates the ease and rapid production of objects with complex geometries that would be more difficult and labour consuming for traditional subtractive manufacturing processes. Industry 4.0 is anticipated to be Nomenclature: k, negative inverse slope; N f , number of cycles to failure; N Ref , reference number of cycles to failure (N Ref = 2·10 6 cycles to failure); P S , probability of survival; R, stress ratio (R = σ min /σ max ); SD, standard deviation; T σ , scatter ratio of the endurance limit, σ max , for 90% and 10% probabilities of survival; θ R , raster angle; σ max , maximum stress in the fatigue cycle; σ MAX,99% , endurance limit at N Ref cycles to failure in terms of σ max ; σ min , minimum stress in the fatigue cycle; σ UTS , ultimate tensile strength

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“…Compared with the test results, the traditional hot spot stress was found to be close to the nominal flexural stress and therefore overly conservative in predicting the fatigue strength of transverse fillet joints in bending. Zamzami et al 4 investigated comprehensively the accuracy and reliability of nominal stress method, hot spot stress method, effective notch stress and notch stress intensity factor method in evaluating fatigue life of a series of aluminium cruciform specimens under bending loading. It was found that the traditional nominal stress and hot spot stress methods could not accurately evaluate the fatigue of cruciform specimens under bending loading.…”

Section: Introductionmentioning

confidence: 99%

A semi‐analytical formula for calculating the notch stress field of cruciform welded joint under bending loading

Shen

Qiu

et al. 2020

Fatigue Fract Eng Mat Struct

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A fine finite element model should be established in fatigue assessment of cruciform welded specimens in notch stress method, and there is no analytical or empirical notch stress formula suitable for engineering application. Based on linear elastic fracture mechanics (LEFM) and singular strength theory, this paper put forward a simple semi-analytical formula of notch stress for commonly used cruciform joints. Considering the influence of incision types and different opening angles, the proposed formula is further extended to U-shaped notch and other common opening angles. After a series of verification, it is found that the proposed semi-analytical stress formula based on singular strength values can simply and accurately predict the notch stress under bending loading, which provides a simple assessment approach for fatigue assessment of cruciform welded joints in engineering.

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On the accuracy of nominal, structural, and local stress based approaches in designing aluminium welded joints against fatigue

Cited by 42 publications

References 41 publications

Fatigue strength of additively manufactured polylactide (PLA): effect of raster angle and non-zero mean stresses

Fatigue strength of additively manufactured polylactide (PLA): effect of raster angle and non-zero mean stresses

Reference strength values to design against static and fatigue loading polylactide additively manufactured with in‐fill level equal to 100%

A semi‐analytical formula for calculating the notch stress field of cruciform welded joint under bending loading

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