Joerg Bagdahn

Laser Powder Bed Fusion (L-PBF) parts combine geometric freedom with process-induced rough surfaces that challenge residual-stress metrology. We evaluated the accuracy of the incremental hole-drilling (IHD) method with electronic speckle pattern interferometry (ESPI) by applying defined stresses via four-point bending to stress-relieved AlSi10Mg coupons, rather than measuring unknown process stresses. Flat specimens (2 mm, thin per ASTM E837) were analyzed on up-skin, side-skin, and CNC-milled surfaces; thin-specimen calibration coefficients were used. After a preliminary inter-specimen check (three specimens per surface; spread < 8 MPa), one representative specimen per surface was tested with three drill sites to assess intra-specimen uniformity. Measured IHD–ESPI stresses agreed best at 70 MPa: deviations were ~4.1% (up-skin), 6.0% (side-skin), and 6.24% (CNC-milled). At 10 MPa the relative errors increased (23.6%, 18.4%, and 1.40%), consistent with reduced ESPI signal-to-noise and fixture compliance in the low-stress regime. At 140 MPa, deviations rose again (21.1%, 14.3%, and 13.1%), reflecting operation near the ~60% Rp0.2 elastic limit of hole-drilling and potential local plasticity. Surface-dependent artifacts also mattered as follows: the side-skin required no coating and performed comparably to CNC-milled, whereas the up-skin’s roughness plus matting spray introduced fringe distortions and chip/coating debris near the hole. This controlled study indicates that IHD–ESPI can provide reliable results on L-PBF AlSi10Mg in the mid-stress range when surface preparation, coating, and rig compliance are carefully managed. Limitations include excluding down-skin surfaces and testing only one specimen per condition; thus, results should be generalized cautiously.

This study examines the impact of different hatching strategies on the mechanical and technological properties, as well as the manufacturing-induced residual stresses of additively manufactured AlSi10Mg components produced using Laser Powder Bed Fusion (LPBF). For the sample production, parallel and orthogonal hatching patterns were employed at various rotation angles, leading to differences in the mechanical properties of the components. The parallel structure exhibits significantly higher compressive residual stresses in the near-surface areas of the component, up to 33% greater than those observed in the orthogonal structure. These compressive residual stresses could counteract operational tensile stresses, potentially enhancing the load-bearing capacity of the component. The findings of this study provide insights into the targeted use of hatching strategies to optimize the mechanical properties and lifespan of components. Future works should focus on experimentally validating the simulation results using the core hole method to further improve the correlation between numerical models and actual stress distributions.

To investigate the soiling behavior of solar energy systems like photovoltaics or concentrated solar power, glass samples were exposed to outdoor conditions in Doha, Qatar for one month. Soil formation on the glass was characterized at microstructural level using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Further, elemental analysis of the crust was done with energy‐dispersive X‐ray spectroscopy (EDX). Small fibrous structures were found on the glass surface and dust particles, providing evidence of a cementation process leading to a strong adhesion of airborne dust particles. In contrast to the common perception, that cementation occurs via the precipitation of salt (sodium chloride) these needle structures were found to be mainly composed of oxides of Si, Mg and Al. This indicates that cementation processes in desert regions are enhanced by the growth of fibrous clay minerals. Cross section of cemented dust particle, connected via small needles to the glass surface. magnified image Cross section of cemented dust particle, connected via small needles to the glass surface.

In recent years, a detrimental degradation mechanism of solar cells in large photovoltaic fields called potential-induced degradation (PID) has been intensively investigated and discussed. Here, the module efficiency is decreasing down to a fractional part of their original efficiency. In this study, we introduce a PID test at a solar-cell level and for individual module components applicable as a tool for process control in industries and root cause analyses in science departments. Using the proposed method, one example analysis of a solar cell that is degraded by the PID tester is presented. It is shown that PID of the shunting type influences both the parallel resistance (Rp) and the depletion region recombination behavior (J02) of the solar cell. Increased recombination in the depletion region is caused by Na decorated stacking faults crossing the depletion region. This strongly influences recombination behavior in the depletion region, leading to an increased J02 and an ideality factor n2 > 2. However, the defects leave the base of the solar cell primarily unaffected, and hence, J ₀₁ recombination remains rather low. Based on these findings, a model for the shunting and the increased depletion region recombination behavior is discussed.