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The purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.

The linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.

As long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.

In future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.

The paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

Large-scale belt-conveyor systems are extensively used in open mines to continuously transport bulk material. Conveyor pulleys are critical components and failures have significant financial consequences due to extended downtime. Aiming at increasing their durability, two critical spots are identified: the drum and the welds between end-plates and drum. Alternative designs have been evaluated. The paper aims to discuss these issues.

Loads on the driving drum are determined from measurements of the bearing force and the motor power. The friction interaction between belt and drum is described by the creep model and its impact is evaluated by comparing the results obtained for low and typical values of friction coefficient. Alternative designs are analysed using finite element method with optimised variable density mesh. The stress field and the deformations are calculated and evaluated.

Friction affects the torque transmission capacity and force distribution, but it is shown that in this case it has almost no impact on the maximum von Mises stress which occurs on the inside surface of the drum; therefore fatigue cracks initiated there, cannot be visually detected. A reinforcing diaphragm is added at the mid-plane to reduce the stress. A new, improved design is proposed to eliminate welds between the end-plates and the drum.

The new proposed design has to be tested in the field to ultimately validate its higher durability.

The impact of the friction of the belt on the drum is demonstrated. The reinforcement resulting from a mid-plane diaphragm is quantitatively evaluated and assessed. A new improved pulley design is proposed aiming at significantly increased operational life compared to the one of the current design.

The purpose of the work is to provide a comprehensive review of the digital image correlation (DIC) technique for those who are interested in performing the DIC technique in the area of manufacturing.

No methodology was used because the paper is a review article.

no fundings.

Herein, the historical development, main strengths and measurement setup of DIC are introduced. Subsequently, the basic principles of the DIC technique are outlined in detail. The analysis of measurement accuracy associated with experimental factors and correlation algorithms is discussed and some useful recommendations for reducing measurement errors are also offered. Then, the utilization of DIC in different manufacturing fields (e.g. cutting, welding, forming and additive manufacturing) is summarized. Finally, the current challenges and prospects of DIC in intelligent manufacturing are discussed.

Integration of Cu/low‐k interconnects into the next‐generation integrated circuit chips, particularly for devices below the 90 nm technology node, has proved necessary to meet the urgent requirements of reducing RC time delay and low power consumption. Accordingly, establishment of feasible and robust packaging technology solutions in relation to the structural design, as well as material selection of the packaging components, has become increasingly important. Moreover, the nature of low‐k materials and the use of lead‐free solder greatly increases the complications in terms of ensuring enhanced packaging level reliability. The foregoing urgent issue needs to be quickly resolved while developing various advanced packages. This paper aims to focus on the issues.

The prediction model, especially for the fatigue life of lead‐free solder joints, combined with virtual design of experiment with factorial analysis was used to obtain the sensitivity information of selecting geometry/material parameters in the proposed low‐k flip‐chip (FC) package. Moreover, a three‐dimensional non‐linear strip finite element model associated with the two levels of specified boundary condition of global‐local technique was adopted to shorten the time of numerical calculation, as well as to give a highly accurate solution.

The results of thermal cycling in experimental testing show good agreement with the simulated analysis. In addition, the sensitivity of analysis indicates that the type of underfill material has a significant effect on the lead‐free solder joint reliability.

A suitable combination of concerned designed factors is suggested in this research to enhance the reliability of low‐k FC packaging with Pb‐free solder joints.

The purpose of this paper is to develop a FE based modeling procedure for describing the mechanical behavior of high‐performance leaf springs made of high‐strength steels under damaging driving manoeuvres.

The type and number of finite elements over the thickness of leaves, as well as the definition of contact, friction and clamping conditions, have been investigated to describe the mechanical behavior in an accurate and time‐effective manner. The proposed modeling procedure is applied on a multi‐leaf spring providing complex geometry and kinematics during operation. The calculation accuracy is verified based on experimental stress results.

A FE based modeling procedure is developed to describe the kinematics and mechanical behavior of high‐performance leaf springs subjected till up to extreme driving loads. Comparison of numerically determined stress distributions with corresponding experimental results for a serial front axle multi‐leaf spring providing complex geometry and subjected to vertical and braking loads confirms high calculation accuracy.

The proposed FE based model is restricted to linear elastic material behavior, which is, however, reasonable for the high‐strength steels used for leaf spring applications.

The proposed FE procedure can be applied for the design and optimization of automotive leaf springs, especially for trucks.

The proposed procedure is simple and can be applied in a very early design stage. It is able to describe accurately the leaf behavior, especially the stiffness and stress response under the most significant driving events. It goes far beyond today's practice for leaf spring design, which is based on analytical methods not covering complex axle and steering kinematics, large deformations and non‐linearities.

Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing.

The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress intensity factor calculation hinges upon a stress field obtained with an image method.

The obtained results are an important step towards the development of a practical tool for crack behaviour prediction in fatigue dominated events.

The results also stress the necessity of improving the experimental techniques to a point where the methods can be applied in real-life solicitations outside of laboratory premises.

Although several research teams around the globe are presently working in this field, the present research topic is original and the proposed methodology has been presented initially by the research team years ago.

The purpose of this paper is to investigate the fatigue and failure of commercial vehicle serial stress-peened leaf springs, emphasizing the technological impact of the material, the thermal treatment and the stress-peening process on the microstructure, the mechanical properties and the fatigue life. Theoretical fatigue analysis determines the influence of each individual technological parameter. Design engineers can assess the effectiveness of each manufacturing process step qualitatively and quantitatively, and derive conclusions regarding its improvement in terms of mechanical properties and fatigue life.

Two different batches of 51CrV4 were examined to account for potential batch influences. Both specimen batches were subjected to the same heat treatment and stress-peening process. Investigations of their microstructure, hardness and residual stress state on the surface’ areas show the effect of the manufacturing process on the mechanical properties. Wöhler curves have been experimentally determined for the design of high-performance leaf springs. Theoretical fatigue analyses reveal the influence of every above mentioned technological factor on the fatigue life of the specimens. Therewith, the effectiveness and potential for further improvement of the manufacturing process steps are assessed.

Microstructural analysis and hardness measurements quantify the decarburization and the degradation of the specimens’ surface properties. The stress-peening process causes significant compressive residual stresses which improve the fatigue life. On the other hand, it also leads to pronounced surface roughness, which reduces the fatigue life. The theoretical fatigue life analysis assesses the mutual effect of these two parameters. Both parameters cancel each other out in regards to the final effect on fatigue life. The sensitivity of the material and the potential for further improvement of both heat treatment and stress peening is appointed.

All quantitative values given here are strictly valid for the present leaf spring batches and should not be widely applied. The results of the present study indicate the sensitivity of high-strength spring steel used here to the various technological factors resulting from the heat treatment and the stress-peening process. In addition, it can be concluded that further research is necessary to improve the two processes (heat treatment process and the stress peening) under serial production conditions.

The microstructure investigations in conjunction with the hardness measurements reveal the significant decrease of the mechanical properties of the highly stressed (failure-critical) tensile surface. Therewith, the potential for improvement of the heat treatment process, e.g. in more neutral and controlled atmosphere, can be derived. In addition, significant potential for improvement of the serially applied stress-peening process is revealed.

The paper shows a systematic procedure to assess every individual manufacturing factor affecting the microstructure, the surface properties and finally, the fatigue life of leaf springs. An essential result is the quantification of the surface decarburization and its influence on the mechanical properties. The methodology proposed and applied within the theoretical fatigue life analysis to quantify the effect of technological factors on the fatigue life of leaf springs can be extended to any engineering component made of high-strength steel.

The purpose of this paper is to describe the results of investigations of parachute rescue systems (PRS) for light gyrocopters.

Although the investigations were conducted in both stages simultaneously, i.e. experimental mechanics approach and numerical simulations, the paper is focussed mainly on the experimental part of the work. To ensure the safety of experimental works (i.e. for both experimenters and bystanders), the authors applied unmanned, remotely controlled scale models of autogyro for the PRS testing in the air.

The critical problem for successful use of the PRS is that the rotation of the rotor blades must be stopped when the main parachute opens, otherwise the influence of the rotor on the improper opening process of the parachute may cause the whole PRS to become useless.

The existing regulations for the use of unmanned aircraft impose the limitation upon the organisation of in-flight tests of PRS, i.e. the maximum take-off mass of the tested gyrocopter models is limited, and a full-scale test needs the approval of European Aviation Safety Agency (EASA).

The research contributes to increasing the safety level for gyrocopter users. The authors elaborated the original PRS, which currently is in the process of patenting.

Originality of the work consists of both an innovative PRS, which has never been tested before, and the results of experimental investigations, which cover both ground tests carried on static or moving stands and in-flight testing.

The purpose of this paper is to describe the development of a contactless and batteryless loading sensor system that can measure the internal loading of an object structure through several covering materials for structural health monitoring.

The paper proposed an architecture by which two radio frequency identification (RFID) tags are used in the system. It has been difficult to realize sensing by RFID because of the low power supply. To solve the power supply problem, a method using functional distribution of RFID tags of two kinds of RFID for communication and power supply was proposed. One RFID tag is specialized as a power supply for communication of strain loading information through A/D conversion. Another is specialized to supply power for driving the strain gauges bridge circuit.

By using developed system, the measurement of the structural internal loading with 20.0 mm depth was possible through covering materials such as concrete, but also plaster board, flexible boards, silicate calcium board, blockboard, and polystyrene with a resolution performance from 10 × 10⁻⁶ to 40 × 10⁻⁶.

A sensor system was developed using passive RFID, which enables measurement of load‐deformation information inside a structural object. Moreover, the inexpensive wireless, batteryless devices used in this system require little maintenance, and applications for the user interface are also included in the developed system for uniform management of structural health monitoring. The developed system was evaluated in an actual situation using not only concrete but also other materials as covering materials on a structural object.

Understanding crack growth in solder joints is important for predicting the fatigue life of solder interconnects. In this paper, crack propagation in solder joints made of two solder alloys, 62Sn/36Pb/2Ag (by weight), a commonly used solder paste for SMT reflow applications, and 96.5Sn/3.5Ag (by weight), a lead‐free solder alloy, was examined during thermal cycling. Based on these observations, the rate of crack propagation was estimated. Microstructural changes in the solder during thermal cycling were also studied.