The in-plane shear behavior of glass fiber-reinforced and carbon fiber-reinforced epoxy (GF- and CF-epoxy) laminates manufactured with the same matrix system is investigated using quasi-static +/- 45 degrees tensile tests. Damage initiation and progression is monitored by optical crack detection for the translucent GF-epoxy and by acoustic emission (AE) analysis for both materials. The study evaluates different criteria for determining the shear stress, , at failure to obtain ply level rather than laminate level strength values and examines the influence of the transverse stress component, , on measured at failure using classical laminate theory. In GF-epoxy, optically observed crack initiation or first-ply-failure (FPF) coincides with a sharp increase in AE activity, enabling an AE-based FPF criterion that more accurately represents ply strength than values from ASTM D3518. Besides the AE-based detection, the ASTM D3039 transition point method provides the most reliable FPF estimates. GF-epoxy exhibits lower at failure than CF-epoxy, consistent with the higher resulting contribution arising from lower orthotropy. For both laminates, the shear modulus of elasticity depends on the selected shear angle, , range due to a gradual decrease in the - slope. In GF-epoxy, maximum AE signal amplitude rate correlates well with optically measured crack density.

In-situ acoustic emission (AE) monitoring of standard quasi-static fracture tests on fiber-reinforced polymer (FRP) composite specimens proves that delamination propagation results from the stochastic occurrence of micro- or meso-scale matrix cracks. The AE signal activity correlates with the observed speed of delamination propagation. Faster delamination propagation hence is rather due to a higher number of matrix cracks per unit time than a significantly increasing average crack size. Approaches for roughly estimating the average size and the size distributions of these matrix cracks with AE monitoring are presented and discussed. This has implications for micromechanical modelling of delamination propagation. The contribution focusses on glass fiber-reinforced epoxy, but the method is also applicable to carbon fiber reinforced thermosets and thermoplastics as well.

This study examines the intrinsic optical enhancements of carbon fiber-reinforced polymers (CFRPs) achieved through the integration of magnesium oxide (MgO) nanoparticles, as well as Mg/MgO and titanium dioxide (TiO2) thin films onto carbon fibers. Integration was performed by quasi-continuous electrophoretic deposition (EPD) and physical vapor deposition (PVD), respectively. Employing a customized electrophoretic cell, EPD facilitated uniform MgO nanoparticle deposition onto unsized carbon fibers, ensuring stable nanoparticle dispersion and precise fiber coating. As a result, the fibers exhibited increased ultraviolet (UV) reflectance, largely attributed to the optical properties of the protective MgO layer. In parallel, PVD enabled the deposition of Mg/MgO and TiO2 thin films with tailored thicknesses, providing precise control over key optical parameters such as reflectivity and interference effects. Mg/MgO coatings demonstrated high UV reflectivity, while TiO2 layers, with their varying refractive indices, generated vibrant colors in the visible (Vis) range through thickness-dependent light interference. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) assessed the quality, thickness, and uniformity of these thin films, and UV/Vis spectroscopy confirmed the influence of deposition parameters on the resulting optical performance. Post-lamination analyses revealed that both EPD and PVD modifications significantly enhanced UV reflectivity and allowed for customizable color effects. This dual strategy underscores the potential of combining EPD and PVD to develop advanced CFRPs with superior UV resistance, decorative optical features, and improved environmental stability.

Damage development in fiber-reinforced polymer-matrix (FRP) composites under service loads is complex. The main reason for this is the micro- and meso-scale morphology interacting with the different microscopic damage mechanisms. Experimental approaches for investigation of microscopic damage mechanisms in FRP are, e.g., X-ray micro-computed tomography and acoustic emission monitoring. While X-ray micro-computed tomography achieves high local spatial resolution (down to sub-micrometer range), essential for identifying the different mechanisms, time-resolution and material volume that can be investigated are limited. Acoustic emission, on the other hand, is applicable to larger specimens and yields high time resolution (below microseconds) but limited spatial resolution only (a few millimeters at best). This contribution discusses which statistical information on microscopic damage in FRP is provided by acoustic emission based on quasi-static fracture mechanics test standards. Pattern recognition applied to acoustic emission signals allows distinguishing different damage mechanisms, e.g., for understanding delamination processes and correlating these with observed fracture surface features. For micromechanical modelling, acoustic emission will answer questions such as, e.g., "What are average microscopic damage sizes during delamination propagation and how much do they vary?" or "Do these damage sizes depend on fracture toughness, specimen load rates, or resulting delamination speed?" This information is relevant for selecting proper spatial and time resolutions for micro-mechanical modelling of damage accumulation in FRP composites.

This study explores innovative methods to alter the optical properties of carbon fiber-reinforced polymer (CFRP) composites. This is achieved through nano- and micro-scale fiber modifications using quasi-continuous electrophoretic deposition (EPD) and physical vapor deposition (PVD). By incorporating carbon fibers with nanoparticles such as silver (Ag) and silica (SiO 2 ) into CFRP laminates significant control over reflectivity and other optical properties is realized. These techniques allow for the precise tuning of optical characteristics, enabling customized visual and functional attributes and potentially improving durability against UV degradation. This research highlights the capability of utilizing EPD and PVD for innovative material design by developing advanced CFRP composites with tailored optical properties for various applications, including potential UV protection of structural components.

Quasi-static delamination resistance tests under Mode I, Mode II and Mixed-Mode I/II loading are performed on unidirectional (UD) glass fiber (GF) and carbon fiber (CF) reinforced polymer laminates manufactured with the same epoxy matrix. Compared to the CF-, the GF-epoxy laminate has a higher fracture toughness under all loading modes. Fracture toughnesses differ the most for Mode II and the least for Mode I loading. Mixed-Mode I/II fracture toughness is determined in Fixed-Ratio Mixed-Mode and Mixed-Mode Bending tests, performed at the same Mixed-Mode I/II ratio of 4:3. The two test methods yield comparable results for UD GF- and UD CF-epoxy.

Variable-density thinning (VDT) can be used to start the conversion of young homogeneous conifer plantations to the single-tree selection system. A design for VDT is presented, which is adapted to harvester-based operations in northern Europe without prior tree marking and the low target diameters in the region. Six treatment cells with a size of 10 x 10 m are placed along a 30 m stretch of a strip road with treatments gap (removing all but understory trees), skip (no thinning), and four treatment cells with crop tree-based crown thinning, which removes two dominant competitors of 1-4 crop trees per cell. Skips might in later thinnings be converted into gaps, which is why skips and gaps are placed systematically in the 2 x 3 treatment blocks. Assignment of the crop tree number variants to treatment cells are decided by the harvester operator based on the given stand structure and presence of crop trees meeting all selection criteria. So far, five operations have confirmed the practicality of this design and given some insight into the learning process of harvester operators with these new methods.

In previous research it has been shown that micro-crack sizes estimated from acoustic emission (AE) data recorded during Mode I interlaminar delamination propagation in a carbon fiber reinforced PEEK and micro-crack sizes seen in video recordings from simultaneously performed X-ray projection radiography with a contrast agent indicate reasonable agreement. Now the approach of estimating crack sizes from AE data is extended to a carbon and a glass fiber reinforced epoxy laminate, using the same matrix. In a first step sensitivity of the AE measurement is estimated based on recorded AE data and estimated delamination area. Different signal filtering approaches are applied to AE data resulting in different estimated sensitivities. Furthermore, assumed delamination area affects sensitivity. Optical microscopy is used to account for roughness of the delamination area. Depending on the assumed sensitivity, average crack size diameters are either slightly below or above 100 µm in both investigated laminates.

Acoustic Emission (AE) has the potential to identify delamination initiation in quasi-static Mode I fracture tests on glass fiber-reinforced polymer-matrix (GFRP) laminates. It had been shown that a combined AE activity and intensity criterion yields critical Mode I delamination resistance values GIC for an AS4/PEEK carbon fiber thermoplastic composite that are comparable to those from data analysis according to ASTM D5528. However, the AE historic index also allows for detection of delamination initiation under Mode I and Mode II loading of carbon fiber reinforced thermoplastics and thermosets. In the present study, these AE criteria for initiation under Mode I, Mode II and Mixed Mode I/II loading of GFRP epoxy laminates are compared with AE signal energy as additional initiation criterion. Initiation under Mode II and Mixed Mode I/II at a ratio of 4:3 was determined with two different set ups for each Mode. For some test configurations noise signals make unambiguous initiation detection difficult. Determination by means of AE energy or AE activity and intensity yields more conservative GC values compared with the AE historic index or criteria defined in the standards, however, with similar repeatability.

Quantitative delamination resistance data of fibre-reinforced polymer-matrix (FRP) composites for quasi-static or cyclic fatigue loads are determined under different loading modes and load rates, respectively. Such data find use, e.g., in FRP materials’ development, materials’ selection, assessment of durability, or structural design. Round robins during test development yielded repeatability and reproducibility (coefficients of variation) of roughly 10 to 25%. This scatter has several different sources. Intrinsic material variability amounts to a few percent at best, at least for advanced manufacturing processes. This intrinsic scatter is essential for material comparisons and structural design. Measurement resolution specified in standardised test procedures yields a maximum of 4–5% variability. Most of the remaining scatter comes from other, extrinsic sources. Test operator actions, e.g., choice of test set-up, manual data acquisition or data analysis can yield extrinsic scatter. Damage mechanisms during delamination initiation and propagation act on the micro- and meso-scale, typically a few micrometer to a few hundred micrometer in size, with corresponding time-scales estimated to between a few tens of nanoseconds and a few microseconds. Defect size-scales are hence several orders of magnitudes lower than test specimen and structural scales, respectively. Predictive capability of models using such test data for structures are, therefore, limited. Major issues are up-scaling from straight beam-like specimens to larger shell-like structures, possibly with complex shape and varying thickness as well as from unidirectional fibre orientation to multidirectional lay-ups.

A working group within the Committee on Acoustic Emission Testing of the German Society for Nondestructive Testing (FA-SEP of DGZfP) has collected published data on the long-term behavior of the AE or the Guided Ultrasonic Wave (GUW) measurement chain (sensor, sensor coupling and mounting, signal transmission, data acquisition and storage). Since only scant data is publicly available, the working group drafted a questionnaire for collecting respective information from the committee members. The returned questionnaires indicate that data acquisition and storage likely pose problems more frequently than other parts of the measurement chain. The only exception noted was for one case of integrity monitoring at elevated temperatures. In this case, sensor sensitivity was observed to decrease compared to the performance at room temperature, requiring the mounting of additional sensors for achieving AE source location with the same resolution. Based on the empirical information, recommendations for long-term monitoring with AE and GUW are discussed. These comprise, e.g., periodic checks of sensors and measurement chain, periodic data back-up, and planning of maintenance and repair.

Specific nano- and micro-scale morphologies of composites can affect the resulting optical and UV reflectivity of the materials. One example is “Vantablack®” made from aligned carbon nanotubes (CNTs) with 99.96% absorption. A similar material with CNTs grown on surface-activated aluminum (CNTs/sa-Al) even yielded 99.995% absorption, one order of magnitude higher than Vantablack®. On the other hand, fresh snow reflects 90% or more of the incident electromagnetic radiation with wavelengths between 400 and 1,000 nm. The reflectivity of snow originates from multiple scattering in the porous morphology made of snow grains. Taking these complex morphologies as inspiration, CFRP epoxy composites with different types, sizes, shapes, and amount of nanoparticles are prepared and compared regarding their optical and ultraviolet (UV) reflectivity. Increasing the reflectivity in the near and far UV may be beneficial for the durability of the epoxy composites, but selective higher or lower reflectivity in certain wavelength ranges may also yield tailored visual effects. Results from different processing approaches with selected nanoparticles are presented and discussed.

Quasi-static or cyclic loading of an artificial starter crack in unidirectionally fibre-reinforced composite test coupons yields fracture mechanics data-the toughness or strain-energy release rate (labelled G)-for characterising delamination initiation and propagation. Thus far, the reproducibility of these tests is typically between 10 and 20%. However, differences in the size and possibly the shape, but also in the fibre lay-up, between test coupons and components or structures raise additional questions: Is G from a coupon test a suitable parameter for describing the behaviour of delaminations in composite structures? Can planar, two-dimensional, delamination propagation in composite plates or shells be properly predicted from essentially one-dimensional propagation in coupons? How does fibre bridging in unidirectionally reinforced test coupons relate to delamination propagation in multidirectional lay-ups of components and structures? How can multiple, localised delaminations-often created by impact in composite structures-and their interaction under service loads with constant or variable amplitudes be accounted for? Does planar delamination propagation depend on laminate thickness, thickness variation or the overall shape of the structure? How does exposure to different, variable service environments affect delamination initiation and propagation? Is the microscopic and mesoscopic morphology of FRP composite structures sufficiently understood for accurate predictive modelling and simulation of delamination behaviour? This contribution will examine selected issues and discuss the consequences for test development and analysis. The discussion indicates that current coupon testing and analysis are unlikely to provide the data for reliable long-term predictions of delamination behaviour in FRP composite structures. The attempts to make the building block design methodology for composite structures more efficient via combinations of experiments and related modelling look promising, but models require input data with low scatter and, even more importantly, insight into the physics of the microscopic damage processes yielding delamination initiation and propagation.

Purpose of Review Forests support most global terrestrial biodiversity and contribute to the livelihood of billions of people, but these and other benefits are in jeopardy due to global change. This leads to questions, such as how to address the challenges of global change in forest management, given the lack of knowledge and deep uncertainty about future developments. In addition, many of the impediments to implement adaptation strategies are unknown. Recent Findings Here, we present an overview of results from a global survey of 754 forestry professionals (370 researchers and educators, 227 practicing foresters, 37 policymakers, 64 administrators, and 56 with other or unspecified roles) from 61 countries across 6 continents who were interested in global change issues. These professionals were asked about their opinion regarding three different adaptation strategies: resist , adapt , and transform . Most respondents agreed that the majority of global change factors will negatively influence the ability of forests to provide desired ecosystem services. Similarly, they agreed about major challenges when implementing adaptation strategies and specifically whether our current knowledge base is sufficient. These concerns were not limited to ecological aspects, but respondents also highlighted the need for a better appreciation of social/political and economic barriers, especially regarding transformation strategies. In addition, the response patterns, including differences due to economic status, highlight the importance of developing and evaluating adaptation strategies in a local social–ecological context. Summary Our study demonstrates a widespread perception on the part of forestry professionals around the world, especially among researchers and practitioners, that many global change factors will affect sustainable forest management negatively, resulting in the need for active silvicultural adaption. The results also suggest potential barriers to different adaptation strategies, particularly a relative lack of information and social acceptance for transform strategies. Further, this study highlights the importance of social and political factors and the need to understand the general public’s values regarding adaptation strategies as well as how the influence of public opinion is perceived by forest managers.

Extending the service life of ageing infrastructure, transportation structures, and processing and manufacturing plants in an era of limited resources has spurred extensive research and development in structural health monitoring systems and their integration. Even though piezoelectric transducers are not the only sensor technology for SHM, they are widely used for data acquisition from, e.g., wave-based or vibrational non-destructive test methods such as ultrasonic guided waves, acoustic emission, electromechanical impedance, vibration monitoring or modal analysis, but also provide electric power via local energy harvesting for equipment operation. Operational environments include mechanical loads, e.g., stress induced deformations and vibrations, but also stochastic events, such as impact of foreign objects, temperature and humidity changes (e.g., daily and seasonal or process-dependent), and electromagnetic interference. All operator actions, correct or erroneous, as well as unintentional interference by unauthorized people, vandalism, or even cyber-attacks, may affect the performance of the transducers. In nuclear power plants, as well as in aerospace, structures and health monitoring systems are exposed to high-energy electromagnetic or particle radiation or (micro-)meteorite impact. Even if environmental effects are not detrimental for the transducers, they may induce large amounts of non-relevant signals, i.e., coming from sources not related to changes in structural integrity. Selected issues discussed comprise the durability of piezoelectric transducers, and of their coupling and mounting, but also detection and elimination of non-relevant signals and signal de-noising. For long-term service, developing concepts for maintenance and repair, or designing robust or redundant SHM systems, are of importance for the reliable long-term operation of transducers for structural health monitoring.

A recently proposed mandrel laminate peel (MLP) test for quantification of delamination propagation in Fiber-Reinforced Polymer (FRP) composites is compared with a climbing drum laminate peel (CDLP) test, and the standard quasi-static Mode I fracture test with Double Cantilever Beam (DCB) specimens. MLP and CDLP both are applicable to thin laminates, for which the Mode I DCB test is not suitable. MLP and CDLP, however, do not yield delamination initiation values. Delamination propagation resistances from the three tests performed with different types of FRP, one partly and one fully cured epoxy laminate, and one thermoplastic laminate, all with unidirectional fiber lay-up agree within about 20%. Reduction of the diameter of the climbing drum (100 mm for the standard climbing drum peel test for adhesives) indicates a minimum diameter on the order of 50 mm for the CDLP test. Additional tests with selected laminates investigated potential effects of specimen width. It is concluded that FRP laminate specimens 20 mm wide and 180 mm long are sufficient for consistent results from CDLP and MLP tests. The CDLP test yielded less scatter (around 10%), i.e., better repeatability than the MLP (round 13%) and the Mode I DCB test (around 17%). Hence, the CDLP test is considered advantageous for industrial application, also due to the simplicity of the test set-up and of the data analysis.

The method of acoustic emission (AE) allows the detection of damage initiation and growth in composites due to its high sensitivity. However, for the same reason, AE signal acquisition can easily be disrupted by ambient noise. A significant source of noise is the testing machine itself. In this contribution, the qualification of different types of testing machines to perform material testing in combination with AE measurements is investigated. For this purpose, quasi-static tensile tests of ±45° carbon fiber-reinforced epoxy specimens are conducted on a static, an electro-dynamic and a servo-hydraulic machine. Static and electro-dynamic machines in the used setup seem to have no influence on AE data acquisition. Contrary, AE data acquisition on the servo-hydraulic machine proves difficult. Measures, such as increasing the threshold for detection or using a highpass filter to reduce noise have a detrimental effect on data acquisition, since desired signals are discriminated as well.

Terrestrial laser scanning of conifer tree crowns is challenged by occlusion problems causing sparse point clouds for many trees. Automatic segmentation of conifer tree crowns from sparse point clouds is a task that has only recently been addressed and not solved in a way that all trees can be segmented automatically without assignment errors. We developed a new segmentation algorithm that is based on region growing from seeds in voxelized 3D laser point clouds. In our data, field measured tree positions and diameters were available as input data to estimate crown cores as seeds for the region growing. In other applications, these seeds can be derived from the laser point cloud. Segmentation success was judged visually in the 3D voxel clouds for 1294 tree crowns of Norway spruce and Scots pine on 24 plots in six mixed species stands. Only about half of the tree crowns had only minor or no segmentation errors allowing to fit concentric crown models. Segmentation errors were most often caused by unsegmented neighbors at the edge of the sample plots. Wrong assignments of crown parts were also more frequent in dense groups of trees and for understory trees. For some trees, point clouds were too sparse to describe the crown. Segmentation success rates were considerably higher for dominant trees in the plot center. Despite the incomplete automatic segmentation of tree crowns, metrics describing crown size and crown shape could be derived for a large number of sample trees. A description of the irregular shape of tree crowns was not possible for most trees due to the sparse point clouds in the upper crown of most trees.

Fracture mechanics data from fiber-reinforced polymer-matrix (FRP) composites are required for damage-tolerant design. Quantifying scatter is essential for determining design limits. Scatter is affected by the "human factor", i.e., process and test operator actions. Intrinsic scatter from manufacture, processing and environment shall be preserved; extrinsic scatter from specimen preparation, test set-up, measurement resolution, and analysis minimized. Automated processes yield fairly consistent scatter, but additive manufacturing of FRP composites has not reached the same maturity level yielding more defects or weak interfaces. The potential of digital technology for reducing scatter and quantifying single and multiple delamination propagation are also discussed.