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Melby presents a formula to predict damage evolution in rubble-mound breakwaters whose armour layer is made of rock, based on the erosion measured in scale-model tests and the characteristics of the incident sea waves in such tests. However, this formula is only valid for armour layers made of rock and for the range of tested sea states. The present work aims to show how the Melby methodology can be used to establish a similar formula for the armour layer damage evolution in a rubble-mound breakwater where tetrapods are employed. For that, a long-duration test series is conducted with a 1:50 scale model of the quay section of the Ericeira Harbour breakwater. The eroded volume of the armour layer was measured using a Kinect position sensor. The damage parameter values measured in the experiments are lower than those predicted by the formulation for rock armour layers. New ap and b coefficients for the Melby formula for the tested armour layer were established based on the minimum root mean square error between the measured and the predicted damage. This work shows also that it is possible to assess the damage evolution in scale-model tests with rubble-mound breakwaters by computing the eroded volume and subsequently, the dimensionless damage parameter based on the equivalent removed armour units.

Based on the Gurson-Tvergaard-Needleman (GTN) damage model, the damage evolution and ductile fracture of 7075 aluminum alloy sheets during the tensile process were predicted. First, the true stress–strain curve and micro morphology of 7075 aluminum alloy at 310 °C∼460 °C were obtained using ultra-high temperature confocal microscope with tensile and compression functions, and the damage characteristics of the fracture position of the tensile specimen were observed by Scanning Electron Microscope (SEM). Then, using the finite element reverse calibration method, the identification method of GTN damage parameters under high temperature was systematically explained and the damage characteristic parameters of 7075 aluminum alloy under high temperature (310 °C∼460 °C) were obtained. The influence of fluctuations in damage parameters on the macroscopic mechanical behavior of materials and the influence of temperature on the value of material damage variables were analyzed. Finally, the void volume fraction of 7075 aluminum alloy at 360 °C was obtained by microscopic observation and compared with the void volume fraction obtained by the finite element reverse calibration method. The results show that the effect of temperature on void volume fraction is basically the same as that of plasticity. The change of void volume fraction has a greater impact on the mechanical properties of the material. There is a small gap between the void volume fraction obtained using the microscopic observation method and the void volume fraction obtained using the finite element reverse calibration method, which verifies the accuracy of the finite element reverse calibration method.

A series of coupled static-dynamic loading tests is carried out in this study to understand the effect of slightly dynamic disturbance on the rocks under high static stress. The acoustic emission (AE) and digital image correlation (DIC) techniques are combined to quantitatively characterize the damage and fracturing behaviors of rocks. The effects of three influencing factors, i.e. initial static stress, disturbance amplitude, and disturbance frequency, on the damage and fracturing evolution are analyzed. The experimental results reveal the great differences in AE characteristics and fracturing behaviors of rocks under static loads and coupled static-dynamic loads. Both the Kaiser effect and Felicity effect are observed during the disturbance loading process. The crack initiation, stable and unstable propagation in the highly-stressed rocks can be triggered by cyclic disturbance loads, and more local tensile splitting cracks are found in the rocks subjected to coupled static-dynamic loads. The damage and fracturing evolution of rocks during cyclic disturbances can be divided into two stages, i.e. steady and accelerated stages, and the increase rate and proportion of each stage are greatly affected by these influencing factors. High initial static stress, low disturbance frequency, and high disturbance amplitude are considered to be adverse factors to the stability of the rocks, which would induce a high increase rate of the steady stage and a high proportion of the accelerated stage within the whole disturbance period. Based on the two-stage damage evolution trend, a linear-exponential damage model is employed to predict the instability of the rocks under coupled static-dynamic loads.

In this paper, we attempts to investigate cutting mechanisms in high-speed cutting of Al6061/SiCp/15p composites using a semi-phenomenologically based damage model in the equivalent homogeneous material (EHM) framework. By combining macroscale EHM modeling and underlying microscale physical mechanisms, a feasible semi-phenomenological plastic model is proposed for prediction of cutting forces and chip morphology during high-speed turning Al6061/SiCp/15p composites. This model incorporates the modified Weibull weakest-link effect to represent the strain-based damage evolution in large deformations. This proposed semi-phenomenological constitutive model is implemented by compiling material subroutines into cutting finite element (FE) codes. The effects of the critical shear stresses on chip formation that depend on the tool-chip frictional coefficient are accounted for in the cutting FE model. The chip formation mechanism affecting material removal behaviors during high-speed turning is further investigated. The capabilities of the proposed constitutive model are evaluated by comparing cutting forces and chip morphologies between experiments and simulations at different cutting speeds associated with strain rates. The EHM-based and microstructure-based models are further compared in both computational efficiency and accuracy. The simulation results show that the developed semi-phenomenological constitutive formalism and cutting model are promising and efficient tools for further investigation of dynamic mechanical and cutting behaviors of particle-reinforced composites with different volume fraction and particle size.

International audience; Understanding and predicting the behaviour of bonded joints under different loading conditions is certainly an aspect of primary importance. Although numerous experimental studies have been carried out over the last few decades, the shear behaviour of bonded joints under cyclic loading has not been investigated in detail. To fill this gap, an extensive experimental and numerical program of double lap shear bonded joints has been carried out. The double lap shear joints were tested under static and cyclic loading to evaluate and compare the influence of external forces on the adhesive performance. The results are discussed in terms of the force-displacement relationship, shear stress, stiffness, residual displacement, and initial damage. Finally, a method is presented for predicting the actual behaviour of double lap shear bonded joints under different loading conditions using an imperfect interface model with damage evolution. The numerical results are in good agreement with the experimental results for all loading conditions. This work has provided and validated an interesting design tool for adhesive structures.

The cable-stayed bridge anchorage system is prone to serious corrosion problems in the offshore environment, threatening its service safety. Based on the copper accelerated salt spray (CASS) test, the anchorage system was subjected to accelerated corrosion and then dissected along the axial direction to study the corrosion damage evolution of the internal structure. This revealed the evolution of corrosion damage in the anchorage system of offshore cable-stayed bridges. The results show that in the offshore environment, a large number of corrosion factors enter the interior of the cable anchorage system through the splicing seam at the junction of the anchor cup and the connecting barrel, and spread to both ends, thus causing corrosion damage to the anchor cup, connecting barrel, filling medium and cable steel wires. Inside the cable of the anchorage system, cross-sections with a higher corrosion level on the outer circle steel wires will also have a higher overall corrosion level. The outer circle steel wires are less able to meet the strength requirements, because they withstand most of the corrosion effects, and the corrosion pits on the surface of the steel wires will render them much weaker than the design tensile strength and fracture. After the CASS test, the ductility of cable steel wires decreases from the inner circle to the outer circle, and the higher the corrosion level of steel wires, the more obvious the brittle indications; the steel wires tend to undergo brittle failure. In the design and manufacture of the cable-stayed bridge anchorage system, special attention should be paid to the corrosion protection of the splicing seam, as well as the corrosion condition and residual strength of steel wires in the outer circle of the cable, to delay the degradation of the mechanical properties and brittle damage of the anchorage system.

In this study, the characteristics of the fracture evolution of argillaceous shale under increasing-amplitude loading were investigated. The GCTS RTR-2000 test system and in-situ acoustic emission (AE) monitoring were employed to execute the tests. The following results were observed. (1) The strength, deformation, and fatigue life increased with the frequency, and the morphology of the hysteresis curve changed regularly with time. (2) The cumulative damage of the rock at the location in which the stress amplitude suddenly increased exceeded that at the fatigue loading stage. The AE count and AE energy were affected by the loading frequency. (3) The secant modulus exhibited different values for different loading frequencies; the smaller the loading frequency, the fewer loading stages the samples experienced, and the faster the secant modulus decreased. The change in Poisson’s ratio over the entire process was composed of a steady growth stage and a rapid growth stage. (4) The rock exhibited two stages of damage evolution, with rapid damage accumulation occurring at the beginning of the loading and relatively smooth damage occurring thereafter. This study developed a cumulative fatigue damage model that can adequately fit the accumulated damage during the fracturing process. The experiments revealed that variable amplitude fatigue loading at different frequencies significantly influences the damage deterioration and the failure law of the rock. The results are expected to improve the understanding of the frequency effect on the fracture behavior and help predict the lifespan of rock structures. This is of great significance to the promotion of slope management, landslide disaster prevention, and mine reuse at the West Open-pit Mine.

To obtain a better economic benefit, Xiadian Gold Mine intended to increase the stope structure parameter from 2.5 m (height) to 8 m. A test stope using the new structure parameter was mined to verify the surrounding rock’s stability. Based on the mechanical indices relating to the ore and rock, the “static” stability of the test stope under the new stope structure was analyzed by the Mathews stability diagram method. Then, a microseismic (MS) monitoring system was installed around the test stope to determine the “dynamic” stability of the test stope during mining. The spatio-temporal evolution of MS events was analyzed to understand the failure behaviors of the surrounding rock. Based on the MS monitoring results, a damage model was established and used to quantify the damage degree and dimension within the surrounding rock during mining the test stope. The study results show that the damage degree increased from less than 0.05 to 0.6, the damage dimension increased from less than 1500 m2 to more than 14,000 m2, and the shear plastic zone appeared around the two sidewalls and the roof of the stope. The results show that the test stope is at risk of instability under the new stope structure.

Ion-irradiated FeCr alloys are useful for understanding and predicting neutron damage in the structural steels of future nuclear reactors. Previous studies have largely focused on the structure of irradiation induced defects, probed by transmission electron microscopy (TEM), as well as changes in mechanical properties. Across these studies, a wide range of irradiation conditions has been employed on samples with different processing histories, which complicates the analysis of the relationship between defect structures and material properties. Furthermore, key properties, such as irradiation-induced changes in thermal transport and lattice strain, are little explored. Here we present a systematic study of Fe3Cr, Fe5Cr and Fe10Cr binary alloys implanted with 20 MeV Fe3+ ions to nominal doses of 0.01 dpa and 0.1 dpa at room temperature. Nanoindentation, transient grating spectroscopy (TGS) and X-ray micro-beam Laue diffraction were used to study the changes in hardness, thermal diffusivity and strain in the material as a function of damage and Cr content. Our results suggest that Cr leads to an increased retention of irradiation-induced defects, causing substantial changes in hardness and lattice strain. However, thermal diffusivity varies little with increasing damage and instead degrades significantly with increasing Cr content in the material. We find significant lattice strains even in samples exposed to a nominal displacement damage of 0.01 dpa. The defect density predicted from the lattice strain measurements is significantly higher than that observed in previous TEM studies, suggesting that TEM may not fully capture the irradiation-induced defect population. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The acoustic emission (AE) method is well studied for its capability to detect and locate discontinuity that evolve in time, when a pressure tank is charged with a greater load than the usual one. When the discontinuity is a crack the AE is able to follow the nucleation and the propagation of the defect in the material. For this paper, experiment on pre-cracked samples with different notch shape are presented. The samples have been loaded with fatigue cycles and the acoustic activity during the tests has been recorded. The stress was always positive to keep the notched side in traction during the test. During the test AE signals become relevant when the load leads plastic strain near the notch. We noticed an increase of activity when the plasticity advances with a stepped shape. This stepped shape of the number of the events versus time agrees very well with the crack nucleation and its evolution to a fully developed crack. We applied the fractal analysis method to these experiments, to verify the correlation between the fractal dimension (Dt), the applied stress and the order/disorder of the material of the sample. The fractal analysis method is capable to follow the damage status of the sample, while fatigue test.

Hot stamping components with tailored mechanical properties have excellent safety-related performance in the field of lightweight manufacturing. In this paper, the constitutive relation and damage evolution of bainite, martensite, and mixed bainite/martensite (B/M) phase were studied. Two-dimensional representative volume element (RVE) models were constructed according to microstructure characteristics. The constitutive relations of individual phases were defined based on the dislocation strengthening theory. Results showed that the damage initiation and evolution of martensite and bainite phases can well described by the Lou-Huh damage criterion (DF2015) determined by the hybrid experimental–numerical method. The calibrated damage parameters of each phase were applied to the numerical simulation, followed by the 2D RVE simulations of B/M phase under different stress states. To study the influence of martensite volume fraction (Vm) and distribution of damage evolution, the void nucleation and growth were evaluated by RVEs and verified by scanning electron microscope (SEM). Three types of void nucleation modes under different stress states were experimentally and numerically studied. The results showed that with the increase of Vm and varying martensite distribution, the nucleation location of voids move from bainite to martensite.

Artikkelissa tarkastellaan evoluutioyhtälöpohjaisen jännitysväsymismallin stokastista laajennusta. Esitetty malli on muodostettu yleisten kontinuumimekaniikan periaatteiden mukaisesti ja on siten luonnostaan moniakselinen ja käsittelee kaikki jännityskomponentit ekvivalentilla tavalla. Malli soveltuu myos mielivaltaiselle kuormitushistorialle. Esimerkkinä tarkastellaan yksinkertaista valkoisella kohinalla häirityn säännollisen kuormituksen aiheuttaman elinikäaennusteen jakaumaa., The article considers the stochastic extension of the evolution equation based continuum approach for fatique. The model is suitable for an arbitrary load history. An example is the simple white noise distribution of the life expectancy forecast caused by the stressed load.

Frost-induced microstructure degradation of rocks is one of the main reasons for the changes in their dynamic mechanical behavior in cold environments. To this end, computed tomography (CT) was performed to quantify the changes in the microstructure of yellow sandstone after freeze–thaw (F–T) action. On this basis, the influence of the microscopic parameters on the dynamic mechanical behavior was studied. The results showed that the strain rate enhanced the dynamic mechanical properties, but the F–T-induced decrease in strength and elastic modulus increased with increasing strain rate. After 40 F–T cycles, the dynamic strength of the samples increased by 41% to 75.6 MPa when the strain rate was increased from 75 to 115 s−1, which is 2.5 times the static strength. Moreover, the dynamic strength and elastic modulus of the sample were linearly and negatively correlated with the fractal dimension and porosity, with the largest decrease rate at 115 s−1, indicating that the microscopic parameters have a crucial influence on dynamic mechanical behavior. When the fractal dimension was increased from 2.56 to 2.67, the dynamic peak strength of the samples under the three impact loads decreased by 43.7 MPa (75 s), 61.8 MPa (95 s), and 71.4 MPa (115 s), respectively. In addition, a damage evolution model under F–T and impact loading was developed considering porosity variation. It was found that the damage development in the sample was highly related to the strain rate and F–T damage. As the strain rate increases, the strain required for damage development gradually decreases with a lower increase rate. In contrast, the strain required for damage development in the sample increases with increasing F–T damage. The research results can be a reference for constructing and maintaining rock structures in cold regions.

The infrared radiation response characteristics and mechanisms of sandstone samples under uniaxial compression were investigated using infrared thermal imaging and strain measurement techniques. The stress–strain curves were divided into different damage stages (i.e., crack closure, elastic deformation, stable crack growth, unstable crack growth, and post-failure) by the damage thresholds determined using the transverse and vertical strains. Experimental results show that the infrared radiation response characteristics of sandstone include the superposition of different mechanisms, which lead to either temperature increase or decrease. The response mechanisms of infrared radiation vary depending on the damage stage. During crack closure and elastic deformation stage, temperature variations are mainly governed by thermoelastic effects and the nearly adiabatic compression of air in the pore space. In the stable and unstable crack growth phase, the temperature variations are dominated by two reverse acting processes: heat production by frictional sliding and cooling by the expansion of gases in pore spaces. This leads to complex inhomogeneous radiation and consequently temperature distribution at the sample surface with local hotspots.

Collision between a moving ship and a bridge in inner rivers is a frequent occurrence that seriously endanger the safety of the bridge. Existing studies mostly address the action of a ship colliding with a bridge pier that is used as a substitution of the associated whole bridge. Such a simplification necessarily induces errors in reflecting the mechanical mechanism and dynamic characteristics of ship–whole bridge collisions. To circumvent this problem, the mechanical behavior of collision between a barge and a whole bridge was studied via elaborating a delicate barge–whole bridge collision simulation underpinned by impact mechanics and materials theories. The main contributions of this study are fourfold: (i) the entire process of the collision between the barge and a whole bridge was fully inspected; (ii) the progressive evolution of collision-induced damage in the bridge pier as well as in the barge was investigated; (iii) the effect of impact velocity, impact angle and barge mass on the collision behavior were elucidated, and (iv) the influences of the superstructure of the whole bridge on the peak value and temporal feature of the impact force, evolution of damage, and top displacement of the bridge pier were clarified. This study yielded more accurate, comprehensive, and reliable results on dynamics and damage evolution of collision in comparison with the outcome of a barge colliding a pier. These findings collectively reveal the mechanical mechanism and dynamic characteristics of collision, providing a scientific basis for developing post-collision damage assessment methods and anti-collision facilities.

Porous asphalt (PA) mixtures are designed with a high air void (AV) (i.e., 18~22%) content allowing rainwater to infiltrate into their internal structures. Therefore, PA mixtures are more sensitive to moisture damage than traditional densely graded asphalt mixtures. However, the moisture damage evolution of PA mixtures is still unclear. The objective of this study was to investigate the moisture damage evolution and durability damage evolution of PA mixtures. The indirect tensile test (ITT), ITT fatigue test, and Cantabro loss test were used to evaluate the moisture sensitivity and durability of PA mixtures, and a staged ITT fatigue test was developed to investigate the damage evolutions under dry and wet conditions. Indirect tensile strength (ITS), fatigue life, indirect tensile resilience modulus (E), and durability decreased with the increment of moisture damage and loading cycles. The fatigue life is more sensitive to the moisture damage. The largest decrements in ITS and E were found in the first 3000 loading cycles, and PA mixtures tended to fail when the decrement exceeded 60%. Damage factors based on the ITS and E are proposed to predict the loading history of PA mixtures. The durability damage evolution and damage factors could fit an exponential model under dry conditions. Moisture had a significant influence and an acceleration function on the moisture damage evolution and durability damage evolution of PA mixtures.

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage, however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

Cast steel is commonly used to produce structural and safety parts. Foundry processes allow producing parts from scrap steel directly to the required dimensions without any forming operation. Cast components may, however, exhibit macro- and micro-shrinkage porosities. The combined effect of macro- and micro-shrinkages on the fatigue behavior of cast steel has been characterized in the literature. Macro-shrinkages may nowadays be eliminated by adequate positioning of risers. However, micro-shrinkages will always be present in cast steel components. Present work addresses the influence of micro-shrinkage porosity on a G20Mn5 cast steel. G20Mn5 (normalized) ingots have been cast under industrial conditions, but ensuring the absence of macro-porosities. Solidification leads to two very different microstructures prior to the normalization treatment: columnar dendrites beneath the surface (Skin) and equiaxed microstructures close to the center (Core). First, metallographic observations of the whole ingot revealed the same grain size in both areas. Fatigue samples were extracted, by differentiating two sampling volumes corresponding to columnar (S) and equiaxed solidification (C), respectively. The distribution of micro-porosities was determined on all samples by Micro-CT-scans. Core samples exhibit micro-porosities with volumes 1.7 larger than Skin samples. Low cycle fatigue tests (3 levels of fixed plastic strain) were run on both sample series (C, S). Results follow a Manson–Coffin law. Core specimens exhibit lower fatigue life than Skin specimens. The differences in fatigue life have been related successfully to the differences in micro-porosities sizes.

Thermoplastic composites (TPCs) are predestined for use in lightweight structures, for example, in automotive engineering, due to their good specific mechanical properties. In many areas of lightweight design, the use of metal inserts for load introduction into composite structures has become established. The inserts can be embedded during composite manufacturing without fibre damage. The technology is based on the concept of moulding holes with a pin tool and simultaneously placing the insert in the moulded hole. The embedding process results in a complex material structure in the joining zone with inhomogeneous three-dimensional fibre orientation and locally varying fibre content. The local material structure has a significant influence on the mechanical behaviour of the joining zone. For this reason, in situ computed tomography (CT) analyses are conducted in this work for a better understanding of the damage behaviour in the joining zone. In situ CT push-out tests were carried in the two thickness directions of along and opposed to the direction of the embedding process. The characteristic local material structure in the joining zone led to direction-dependent damage behaviour based on different failure modes.

In order to explore the mechanical characteristics of confined-pressure soaking (CPS) sandstone during the damage-fracture process, the uniaxial compression and acoustic emission (AE) experiment of CPS sandstone was conducted. The mechanical parameters, fracture morphology, AE and energy characteristics under uniaxial stress were researched. The results show that the uniaxial compressive strength and elastic modulus decrease as a logarithmic function with CPS parameters, corresponding to the inflection point of modification. The fracture mode gradually changes from brittleness to toughness with the increase in moisture content. The difference between fracture fragmentation and mechanical behavior mainly depends on the degree of CPS. The evolution of AE characteristics and energy dissipation has a good correspondence with CPS specimens. The higher the CPS degree is, the less the AE cumulative number is and the longer the excitation time is. Based on the phase variation of AE events and energy dissipation, the CPS damage variables are proposed to quantify the weakening degree and reveal the damage evolution process. The results provide a useful foundation for evaluating rock failure and improving service life.

Carbon Fiber Reinforced Plastic (CFRP) shaft tube structure is widely applied in different fields, including aerospace, automotive, and wind power. Since CFRP shaft tube is often subjected to bending fatigue loads, it is of great significance to research its bending fatigue characteristics. Because of its unique advantages, such as a smaller size, lighter weight, and the outstanding ability to form a sensor network, the Fiber Bragg Grating (FBG) sensor is very applicable for health monitoring research of composite material structures. Taking the CFRP shaft tube under bending load as the research object, based on the theory of composite material mechanics and applying the research idea of combining simulation analysis and experiment, the fatigue life, residual stiffness, and fatigue damage evolution of CFRP tubes under three-point bending fatigue loading were studied. Moreover, the fatigue characteristics of CFRP tubes under different fatigue loading were analyzed. At the same time, the ultrasonic phased array was used to obtain the fatigue damage evolution rule by scanning and analyzing the damage to the CFRP shaft tube after different fatigue loading times. Through the application of the FBG sensors, the whole process of fatigue evolution of the CFRP shaft tube was fully monitored.

Composed of metallic layers and composite plies, fiber metal laminates (FMLs) combine inherent advantages of metals and composites. The phenomenon of anomalous response behavior, in which the permanent deformation is in the opposite direction to the incoming pressure wave, has been discovered in dynamic responses of monolithic plate subjected to impulsive loading. In this study, dynamic responses of FML plates of various configurations are examined and compared against the responses of a monolithic plate using finite element analysis. It is found that under the load condition in which an anomalous dynamic behavior of an aluminum plate is observed, FMLs oscillate a few cycles before resting on permanent deformation, and the laminate thickness strongly affects the final deflection, which could be in the counter-intuitive direction or near the initial position of zero deflection depending on configuration and specification of FMLs. In addition, interaction of damage accumulation with deflection responses is investigated. The findings of this study can be useful for optimal design of FMLs intended for usage under extreme loadings.

The initiation and progression of fiber damage in on-axis UD glass/epoxy materials under fatigue loading conditions were studied. Uniaxial tension–tension fatigue tests at different load levels were carried out to monitor the fiber damage evolution through the fatigue lifetime. The damage evolution was quantified by initial fiber breaks, the evolution of fiber breaks, fragmentation and clustering progression. Through qualitative and quantitative analyses, it is shown how the fiber damage evolution depends on the number of cycles, the applied load level and the number of broken fibers during the first cycle.

3D imaging techniques have an enormous potential to understand the microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this conference paper we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. We demonstrate showcases of ceramics and composite materials, where microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. We present in situ analysis of the damage evolution in an Al/Al2O3 metal matrix composite during tensile load and the identification of void formation (different kinds of defects, particularly unsintered powder hidden in pores, and small inhomogeneity’s like cracks) in Ti64 parts produced by selective laser melting using synchrotron X-ray refraction radiography and tomography.

In the present work, cross-ply and multidirectional laminates were produced by autoclave moulding. Changes in the process parameters led to different microstructural features in terms of fibre volume fraction, global void content, and void size. Fatigue tests revealed a strong influence of the microstructure on the long-term performances of the laminates, in terms of life to crack initiation, crack propagation, crack density evolution and associated stiffness drop. A criterion recently proposed by the authors to predict the formation of the first fatigue cracks accounting for the actual material microstructure, including voids, was then validated on the new experimental data. The results show the need to properly account for the manufacturing induced defects for a more efficient and safer design of composite parts, and remark the necessity of developing models that link manufacturing process parameters, micro-scale morphology, and mechanical performances to enable a cost-effective production that maximizes the performance/cost ratio.

This paper focuses on the vulnerability assessment of a civic tower built in 1512, which is now considered a national monument. It is the original bell tower of S. Ambrogio church that was destroyed in 1809. Experimental investigations have been carried out on this historical tower. First, detailed investigations have been carried out to identify the geometry of the tower as well as the mechanical features of the constituting materials. Then, ambient vibration tests have been applied using five Micro Electro-Mechanical Systems (MEMS) sensors to detect of the main dynamic features, e.g., modal parameters and damping. Two output-only identification methods, including Frequency Domain Decomposition and Random Decrement Techniques, have been used. The outcomes of the modal identification have been employed to inform the FE model. The numerical analysis can be used for vulnerability assessment, providing a valuable picture of possible damage evolution, tower collapse mechanism, and subsequently, useful hints for the execution of structural retrofitting strategies.

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

The paper conducted bearing tests on composite pinned joints with four different stacking sequences. The bearing strength and bearing chord stiffness were obtained. The influence of stacking sequences on failure modes, bearing strength and bearing chord stiffness was discussed. Based on continuum damage mechanics, a three-dimensional finite element model of composite pinned joint under bearing load was built, where the maximum strain criterion was employed for initiation and bi-liner damage constitutive relation for revolution of fiber damage, while the physical-based Puck criterion was used for matrix damage initiation, and matrix damage revolution depended on the effective strain on the fracture plane. The failure mode, bearing strength and bearing chord stiffness of composite pinned joint were discussed with this model under which the non-linear shear behavior and in-situ strength effects were considered. Good agreements between test results and numerical simulations validates the accuracy and applicability of the finite element model.

International audience; In this work, we present a model for the initiation and evolution of damage for a composite fibre-reinforced pipe used in the Oil & Gas industry, based on a commercially available pipe. A continuum damage mechanics model was employed to determine the initiation and evolution of damage. This model was implemented using finite element analysis to investigate the performance of the commercial composite pipe. Initially, the material properties were obtained from experimental data and fitting with static structural simulations. Then, FE simulations with damage were performed, considering three different boundary conditions: open, closed (pressure-vessel type) and fixed ends, the load considered was internal pressure. Results showed differences not only in the stress distribution but on the damage initiation and evolution along the geometry of the pipe. These differences in the damage initiation and propagation can be explained as the result of different axial-hoop stress ratio.

This paper focuses on a study of different methodologies for surveying two-dimensional scale models of rubble mound breakwaters. Tests were conducted in one of the LNEC’s irregular wave flumes and involved the use of four different methodologies using photogrammetric and 3D scanning techniques. This paper describes the materials and methods used during the experiments, as well as the results obtained. The data analysis contains the profiles and comparison of the meshes used in each of the techniques, in order to evaluate their application in scale model tests of rubble mound breakwaters. Also, the specific experimental conditions needed for using each of these techniques were investigated.

Material viscoelasticity is of particular importance for polymers, biotissues and many others, due to the significant influence not only on the elastic response of structures, but also on their failure mechanism in actual applications. In this study, the experimental tests by nanoindentations are categorized according to the objective parameter combined with the indenter shape into four distinct cases, and the Fractional Derivative Zener model (FDZM) is employed to characterize this time-dependent property. The explicit data-fitting formulas are derived to determine the relaxation modulus and creep compliance tested with the conical and spherical indenters. Besides, a fitting scheme is provided to facilitate the identification of these viscoelastic parameters. In comparison with the general methods adopting the Prony series or empirical models, two silent merits present: (1) fewer model coefficients necessitate being determined based on the experimental data; (2) the relaxation modulus G(t) and the creep compliance J(t) can be obtained through one indentation test, and their exact interconversion is guaranteed as well. Several sets of experimental data are applied to examine the validity of the developed approach, and three more examples are adopted to demonstrate the exact interconversion between G(t) and J(t). A few concluding remarks are drawn eventually.

In this study, layered n-layer fiber-reinforced (L-nLFR) Ti–Al composites mimicking portion II of the locust semilunar process (SLP) with excellent mechanical properties were designed, and the finite element method was used to determine the influences of the total volume content of Ti (VTi), volume content of layered Ti (VLTi), and number of fiber layers (n) on the specific bending strength and fracture bending strain of the L-nLFR Ti–Al composite structures. The results showed that increasing VTi from 0.1 to 0.6 and VLTi from 0 to VTi significantly increases the specific bending strength but has a non-monotonic effect on the fracture bending strain of the structures. Increasing n from 1 to 2 significantly increases the specific bending strength but reduces the fracture bending strain, and the increase of n from 2 to 5 can reduce the damage evolution rate. Compared to multilayer Ti–Al composite structures in previous studies with approximately equal specific bending strengths, the fracture bending strain of the L-nLFR structure is 15%-20% larger. The biomimetic layered fiber-reinforced Ti-Al composites designed in this study can provide a new choice for engineering composite materials.

This paper presents a framework combining theoretical, numerical, and experimental approaches for evaluating the remaining-life of high-rise steel buildings based on earthquake-induced fatigue damage propagation in local beam-to-column connections. A mesh-independent finite element model is developed and implemented using the concept of lumped damage mechanics to estimate the fatigue-induced life loss associated with the extent of crack propagation until complete rupture failure occurred in beam-to-column connection substructure of high-rises. In this framework, a damage state variable is introduced at each end of beam elements and can be linked to the extension of the fatigue fracture in real frame building joints. Then, the damage evolution law is developed by extending the conventional Manson–Coffin law and a new crack-driving parameter to quantify the extent of damage states and predict the remaining life of the associated components in high-rises buildings. The proposed model is validated by a damage index measured from the local wireless sensors in substructure tests of ductile steel beam-to-column connections subjected to ultra-low cycle fatigue loadings. The residual resistance can be quantified by updating the damage curve with the identified damaged conditions.

A parametric finite element model (FEM) of three-dimensional five-directional (3D5d) braided composites was established considering the yarn space contact relationship. By adopting reasonable damage criteria and boundary conditions, the damage behavior and mechanical properties of FEM under tensile loading were investigated. The finite element prediction results are consistent with the experiments, indicating that the FEM can effectively predict the progressive damage and strength of 3D5d braided composites. Damage evolution shows that the main failure modes with small braiding angles include tensile failure of braiding yarn and axial yarn, while the large braiding angles are tensile shear failure of braiding yarn. As the fiber volume fraction increases, the initial damage location of the FEM changes from the intersection of braiding yarn/axial yarn to the junction among the braiding yarns. The stress-strain curves results show that the 3D5d braided composites exhibit brittle fracture characteristics under longitudinal tensile loading, and the mechanical properties are significantly correlated with the braiding angle and fiber volume fraction. In addition, the tensile properties of 3D5d braided composites are also compared with those of three-dimensional four-directional (3D4d) braided composites.

In order to describe the fatigue damage state of asphalt mixture more reasonably, direct tensile tests of the fatigue and the residual strength under stress levels of 1.00 MPa, 0.50 MPa and 0.25 MPa with five parallel tests were carried out. The trabecular specimens of AC-13C asphalt mixture (25 cm &times, 5 cm &times, 5 cm) were manufactured with Styrene-Butadiene-Styrene (SBS) modified asphalt, aggregate basalt and limestone mineral filler. The optimum asphalt-aggregate ratio was 5.2%. The dynamic modulus decay and the residual strength decay were termed as the damage variables to evaluate the fatigue damage process of asphalt mixtures, respectively. Based on the test results, the decay patterns of the dynamic modulus and the residual strength during fatigue tests under different stress states were revealed, and the model and the parameters of fatigue damage according to the corresponding decay patterns were obtained. Then, based on the assumption that the residual strength and dynamic modulus depend on the same damage state, the relationship between the two damage definitions was given, and the residual strength-dynamic modulus coupled model was established. The results showed that the residual strength-dynamic modulus coupled model could better describe the fatigue damage evolution law of asphalt mixture, and the parameter of this coupled model could be obtained by less residual strength tests. A modified formula for calculating the damage variables associated with residual strength and dynamic modulus was proposed based on the relationship between two kinds of damage variables.

Composite structures undergo a gradual damage evolution from initial inter-fibre cracks to extended damage up to failure. However, most composites could remain in service despite the existence of damage. Prerequisite for a service extension is a reliable and component-specific damage identification. Therefore, a vibration-based damage identification method is presented that takes into consideration the gradual damage behaviour and the resulting changes of the structural dynamic behaviour of composite rotors. These changes are transformed into a sequence of distinct states and used as an input database for three diagnostic models, based on the Kullback&ndash, Leibler divergence, the two-sample Kolmogorov&ndash, Smirnov test and a statistical hidden Markov model. To identify the present damage state based on the damage-dependent modal properties, a sequence-based diagnostic system has been developed, which estimates the similarity between the present unclassified sequence and obtained sequences of damage-dependent vibration responses. The diagnostic performance evaluation delivers promising results for the further development of the proposed diagnostic method.

The effect of stress state on the initiation of damage for leaded free cutting steel has been investigated under hot rolling conditions. Double notched (DN) circumferential tension samples were designed and used to simulate damage development at different stress states and deformation conditions using a Gleeble (3800) thermal-mechanical testing system. Two DN sample geometries with varying notch profiles were used to account for different states of stress. To simulate the conditions of hot rolling the samples were tested at high temperatures (900–1200 °C) and moderate strain rates (0.1–1 s−1). After testing to failure, which normally occurs at one notch of the specimen, the unfailed notch of each sample was sectioned to examine the sites where damage occurs since the material has been captured in a state very close to failure. Two of the cases examined have shown definitive damage paths occurring from ‘outside–in’ for a sharp notch deformed at T = 900 °C and from ‘inside–out’ for a blunt notch tested at T = 1200 °C for the same strain rate of 0.1 s−1. The experimental results of the failure initiation sites were compared with computed values of the stress fields around the notch profiles, obtained from FE analysis using a set of viscoplastic constitutive equations calibrated for free cutting steel. The temperature profiles from high temperature mechanical testing were used in the FE calculations of the stress state.

In this paper, the fatigue behaviour of different polypropylene compounds, characterized by different fractions of recycled material, were analysed. Fully reversed fatigue tests were carried out on three different polypropylene (PP) compounds, namely a 42 wt% calcium carbonate filled PP (EA209), a 42 wt% calcium carbonate filled polypropylene containing 25% recycled PP (R2025) and a 42 wt% calcium carbonate filled 100% recycled polypropylene (R2100). Both plain and notched samples were tested. In particular, the notch sensitivity was investigated on double-edge notched specimens machined from 5-mm-thick injected moulded plates. Three different notch geometries were analysed, namely a 10 mm circular notch radius (Kt=1.65), a 2 mm U-notch radius (Kt=3.17) and a 0.5 mm V-notch radius (Kt=5.97). During the experimental tests, the fatigue damage evolution was monitored by using on board travelling microscope and, after failure, fracture surfaces were analysed as well. In view of this extensive body of evidence, it was concluded that the analysed PP compounds are notch insensitive. The presence of 25% recycled PP slightly influenced the fatigue behaviour with respect to the compound made of virgin PP. Consequently, in the present paper, a single design-stress-life curve was proposed for EA209 and R2025 plain and notched compounds, characterised by an inverse slope, k, equal to 13 and a reference net stress amplitude evaluated at 2 million cycles, σA,50%, equal to 11 MPa. Conversely, a down-graded stress-life design curve was determined for R2100 compound, having k=16 and σA,50%=8 MPa. Finally, the fatigue damage analysis highlighted that damage mechanisms and their evolution were independent on the type of material and notch radius and consisted of void formation and coalescence.

To study the dynamic mechanical characteristics and constitutive relation of concrete materials under freeze&ndash, thaw (FT) cycle conditions, C35 concrete was taken as the research object in this paper, and FT tests were carried out with a freeze&ndash, thaw range of &minus, 20&ndash, 20 &deg, C and a freeze&ndash, thaw frequency up to 50 times. By using the separated Hopkinson pressure bar (SHPB) system, impact compression tests of concrete specimens under different FT cycle actions were developed, then the dynamic fracture morphology, fracture block distribution, stress&ndash, strain curve, peak stress and other dynamic mechanical properties of concrete were analyzed, and the influence law of FT action and strain rate was obtained. Through introducing the freeze&ndash, thaw deterioration damage factor and the stress damage variable, the dynamic visco-elastic damage constitutive equation of freeze&ndash, thawed concrete was constructed based on component combination theory. Furthermore, the damage evolution process and mechanism of freeze&ndash, thawed concrete materials were revealed. The research results show that the dynamic mechanical properties of concrete under a freeze&ndash, thaw environment are the combined results of the freeze&ndash, thaw deterioration effect and the strain rate strengthening effect. The dynamic visco-elastic damage constitutive model established in this paper can effectively describe the dynamic mechanical properties of freeze&ndash, thawed concrete, and has the characteristics of few parameters and good effect. The stress damage evolution path of concrete goes backward with the increase of FT cycles and the development speed gradually slows down. The greater the difference in FT cycles, the greater the difference in stress damage path.

Crashworthiness is the ability of a structure to withstand a crash event ensuring the safety of its passengers. The aim of this work is to investigate the damage onset and evolution in a composite fuselage barrel undergoing a vertical drop test on a rigid surface. The mechanical behaviour of the barrel has been assessed by means of a Numerical-Experimental study. Indeed, the experimental data from a full scale barrel test, performed at the CIRA facilities, have been used in conjunction with numerical results, obtained by means of an advanced 3D FEM model, to investigate, in detail, the deformations and the damage development during the crash event. The adopted three-dimensional numerical model, based on an explicit FE formulation, uses Continuum Shell elements and CDM to take into account the onset and the evolution of the intra-laminar damages in each subcomponent of the investigated composite fuselage barrel. The obtained numerical results have been compared with experimental data in terms of accelerations, displacements and deformations to provide a preliminary validation of the adopted FEM model. A special attention has been given to sub-components which demonstrated to mainly influence the global mechanical behaviour of the investigated composite fuselage barrel during the experimental test.

Investigations of the fatigue performance of composite materials have accompanied their introduction in several engineering domains since the 1950s. An abundance of publications have emerged dealing with the experimental investigation of the fatigue performance of composites under different loading and environmental conditions, as well as the development of theories for the modeling of the fatigue behavior and/or prediction of the fatigue life of the materials systems under consideration. This work aims to briefly review and present the history of fiber-reinforced polymer composite laminate fatigue investigations, dividing the last 70 years into three periods. The early 1950–1975 period, when the “new” materials and their behavior under (simple) fatigue loading patterns were discovered. The mature, 1975–2000 period, when more loading and material parameters were investigated and the basic theoretical background was established. And finally, the later period, in the new millennium, when more detailed experimental campaigns were performed (assisted by developments in a multitude of engineering and scientific fields) and parameters that had previously been overlooked by researchers were taken into account.

The deformation and failure of coal and rock materials is the primary cause of many engineering disasters. How to accurately and effectively monitor and forecast the damage evolution process of coal and rock mass, and form a set of prediction methods and prediction indicators is an urgent engineering problems to be solved in the field of rock mechanics and engineering. As a form of energy dissipation in the deformation process of coal and rock, microseismic (MS) can indirectly reflect the damage of coal and rock. In order to analyze the relationship between the damage degree of coal and rock and time-frequency characteristics of MS, the deformation and fracture process of coal and rock materials under different loading modes was tested. The time-frequency characteristics and generation mechanism of MS were analyzed under different loading stages. Meanwhile, the influences of properties of coal and rock materials on MS signals were studied. Results show that there is an evident mode cutoff point between high-frequency and low-frequency MS signals. The properties of coal and rock, such as the development degree of the original fracture, particle size and dense degree have a decisive influence on the amplitude, frequency, energy and other characteristic parameters of MS signals. The change of MS parameters is closely related to material damage, but has no strong relation with the loading rate. The richness of MS signals before the main fracture depends on the homogeneity of materials. With the increase of damage, the energy release rate increases, which can lead to the widening of MS signals spectrum. The stiffness and natural frequency of specimens decreases correspondingly. Meanwhile, the main reason that the dominant frequency of MS detected by sensors installed on the surface of coal and rock materials is mainly low-frequency is friction loss and the resonance effect. In addition, the spectrum and energy evolution of MS can be used as a characterization method of the damage degree of coal and rock materials. Furthermore, the results can provide important reference for prediction and early warning of some rock engineering disasters.

Microcracks in concrete can coalesce into larger cracks that further propagate under repetitive load cycles. Complex process of crack formation and growth are essentially involved in the failure mechanism of concrete. Understanding the crack formation and propagation is one of the core issues in fatigue damage evaluation of concrete materials and components. In this regard, a numerical model was formulated to simulate the thorough failure process, ranging from microcracks growth, crack coalescence, macrocrack formation and propagation, to the final rupture. This model is applied to simulate the fatigue rupture of three-point bending concrete beams at different stress levels. Numerical results are qualitatively consistent with the experimental observations published in literature. Furthermore, in the framework of damage mechanics, one damage variable is defined to reflect stiffness reduction caused by fatigue loading. S-N curve is subsequently computed and the macroscopic damage evolution of concrete beams are achieved. By employing the combined approaches of fracture mechanics and damage mechanics, made possible is the damage evolution of concrete beam as well as the microscopic multiple fatigue crack simulation. The proposed approach has the potential to be applied to the fatigue life assessment of materials and components at various scales in engineering practice.

Here In this study, the composite laminates subjected to transverse impact with consideration interlaminar and intralaminar damage based on Cohesive Zone Model (CZM) and Progressive Damage Model (PDM) are investigated by numerical analysis using ABAQUS commercial finite element code. The delamination in stacking ply with the same fiber orientation is considered as interlaminar damage and the delamination in an inner layer of any cluster is ignored. Hashin criterion is used for intralaminar damage initiation and evolution without using any subroutine. First, the appropriate procedure for delamination on composite specimen was suggested based on CZM approach in double cantilever beam to verify the intralaminar damage simulation. Then by considering several case studies with different impact energies, the results of present simulation is verified with the relevant and available experimental results and numerical references in the existing literature. According to the available experimental results the present simulation results are more acceptable and accurate than the results of similar numerical works, especially in higher impactor velocity.

The threat of delaminations arising during in-service loading conditions is one of the key factors limiting the use of composite materials in large volume for main structures. Delamination occurrence is primarily caused by the interlaminar tension and shear stresses that develop due to different factors. These include geometric or materials discontinuities (e.g. edges, holes, dropped ply), but are also linked to internal mechanism failure, such as matrix cracks. The present thesis focuses on the investigation of the correlation existing between different damage mechanisms occurring in composite laminates. The problem of delamination initiation from transverse cracks in cross-ply laminates under quasi-static loading is thoroughly studied in Chapter 2. An analytical solution is presented for the local mode I, II and III stress fields arising in the close neighbourhoods of a transverse crack, stresses being written as a function of Generalised Stress Intensity Factors (GSIFs). Moreover, a fracture criterion for the delamination onset in cross-ply laminates under tension, based on a critical value for the mode 1 GSIF, is proposed and validated taking advantage of the results from an experimental campaign. The analytical solution describing the stress fields in the adjacencies of a transverse crack, found for cross-ply laminates, was then extended to be suitable to describe the stress fields for laminates with generic orientation (Chapter 3). The results of the research activity focused on the investigation of delamination evolution for composite laminates subjected to cyclic loads are presented in the following chapters. In particular, the outcomes of the experimental tests carried out on glass/epoxy cross ply laminates are presented in Chapter 4. Numerical analyses were performed to characterize the evolution of delamination area during fatigue life. Energy release rates (ERR) associated with delamination growth was calculated by using the virtual crack closure technique (VCCT) and a Paris-like curve was derived (Chapter 5). Furthermore, the reduction of Young's modulus and Poisson's ratio were modelled. Theoretical predictions were found to be consistent with collected experimental data. The process of delamination growth may be affected by different parameters. The presence of the friction sliding between the delaminated interfaces is one of these. The friction effects on ERR values are discussed in the Appendix. Different conditions of damage were numerically simulated, varying the value of the coefficient of friction and the length of delaminations. It was found that the presence of friction was not so influent for the purposes of delamination growth assessment. Then, with the aim of investigating damage evolution for laminates characterized by different orientations, fatigue tests were carried out on [0/452/-452]s and [0/452]s laminates. The different phases of the damage process were documented by collecting a detailed series of images, showing the accumulation of the observed failure modes. During the tests, the Young’s modulus and the Poisson’s ratio evolution were determined and their correlation with the damage evolution was investigated (Chapter 6). Following the approach used for cross-ply laminates, a correlation between the growth rate of delamination and ERR was investigated. Furthermore, a series of numerical investigations in response to the free edge delamination problem was performed. In fact, delamination initiation and growth was observed to occur more extensively near the free edges, both for balanced and unbalanced configuration of laminates. The results of these FE analyses are presented in Chapter 7. Finally, a model based on a probabilistic approach for the prediction of fibre failure of 0° laminae in cross ply laminates subjected to tensile-tensile fatigue loading will be described in Chapter 8.

Damage tolerant design is based on reliable fatigue crack growth methods for both high cycle and low cycle fatigue problems. While the Paris’ law can be applied for estimate crack growth life in quasi-elastic materials, elastic-plastic fatigue crack growth needs more accurate computational models. In the past decade numerous cohesive zone models were proposed and investigated for predicting elastic-plastic fatigue crack growth. However, most cohesive zone models were used to reproduce fatigue crack growth with vanishingly small scale yielding and failed to predict low cycle fatigue crack growth with the finite plastic zone. In the present work a new CCZM is introduced for the high fatigue crack growth rate and attempting to give a uniform description from cyclic fatigue crack growth to elastoplastic rupture in ductile materials. The damage accumulation equation in the cohesive model contains both monotonic damage as well as cyclic damage mechanism. Experimental verification was carried out in an austenitic stainless steel AISI 304 through fracture tests and fatigue crack growth tests of compact tension (CT) specimens under mode I and compact-tension shear (CTS) specimens under mixed mode loading conditions. Detailed finite element computations confirmed that the present cohesive zone model provides a uniform description for the whole fatigue crack growth regimes. The model parameters can be determined in the conventional CT specimens. The cohesive zone model has the potential to be applied for more complex structural failure analysis.

Tensile tests on miniature spruce specimens have been performed by means of acoustic emission (AE) analysis. Stress was applied perpendicular (radial direction) and parallel to the grain. Nine features were selected from the AE frequency spectra. The signals were classified by means of an unsupervised pattern recognition approach, and natural classes of AE signals were identified based on the selected features. The algorithm calculates the numerically best partition based on subset combinations of the features provided for the analysis and leads to the most significant partition including the respective feature combination and the most probable number of clusters. For both specimen types investigated, the pattern recognition technique indicates two AE signal clusters. Cluster A comprises AE signals with a relatively high share of low-frequency components, and the opposite is true for cluster B. It is hypothesized that the signature of rapid and slow crack growths might be the origin for this cluster formation., Holzforschung, 69 (3), ISSN:0018-3830, ISSN:1437-434X

Nowadays recycling is one of the most important keyword to reduce product-costs. In view of this, thermoplastics are very attractive materials for their recycling feasibility. In this paper the static behaviour, the fatigue behaviour and the damage evolution of different polypropylene compounds, characterised by different fractions of recycled material, were investigated. Their fatigue notch sensitivity was analysed as well. Tensile static and fully reversed fatigue tests were carried out on three different material systems, namely a 42 wt% calcium carbonate filled polypropylene (PP), a 42 wt% calcium carbonate filled polypropylene containing 25% recycled PP and a 42 wt% calcium carbonate filled 100% recycled polypropylene. The notch sensitivity was investigated on double-edge notched specimens machined from 5-mm-thick injected moulded plates. Three different notch geometries were analysed, namely a 10 mm semicircular notch radius, a 2 mm U-notch radius and a 0.5 mm V-notch radius. During the experimental tests, the damage evolution was investigated by using an on board travelling microscope. As a result, it was found that all materials are largely notch insensitive in high cycle fatigue.

While many aspects of electronics manufacturing are controlled with great precision, the nucleation of tin in solder joints is currently left to chance. This leads to a widely varying melt undercooling and different crystal orientations in each joint, which results in a different resistance to electromigration, thermomechanical fatigue, and other failure modes in each joint. Here we identify a family of nucleants for tin, prove their effectiveness using a novel droplet solidification technique, and demonstrate an approach to incorporate the nucleants into solder joints to control the orientation of the tin nucleation event. With this approach, it is possible to change tin nucleation from a stochastic to a deterministic process, and to generate single-crystal joints with their c-axis orientation tailored to best combat a selected failure mode., Control over the crystallographic orientation of solder joints based on βSn will improve the reliability of electronic interconnects. Using a technique based on droplet solidification and lattice matching, Ma et al. are able to control the βSn nucleation events, hence control the grain orientation.