A dearth of direct field observations limits our understanding of individual mechanical weathering processes and how they interact. In particular, the specific contributions of solar-induced thermal stresses to mechanical weathering are poorly characterized. Here, we present an 11 mo data set of cracking, using acoustic emissions (AEs), combined with measurements of rock temperature, strain and other environmental conditions, all recorded continuously for a granite boulder resting on the ground in open sun. We also present stresses derived from a numerical model of the temperature and stress fields in the boulder, idealized as a uniform elastic sphere experiencing simple solar temperature forcing. The thermal model is validated using this study's data. Most observed cracking coincides with the timing of calculated maximum, insolationdriven, tensile thermal stresses. We also observe that most cracking occurs when storms, or other weather events, strongly perturb the rock surface temperature field at these times. We hypothesize that these weatheractuated thermal perturbations result in a complex thermal stress distribution that is superimposed on the background stresses arising from simple diurnal forcing; these additive stresses ultimately trigger measurable cracking. Measured locations of observed cracking and surface strain support this hypothesis in that they generally match model-predicted locations of maximum solar-induced tensile stresses. Also, recorded rock surface strain scales with diurnal temperature cycling and records progressive, cumulative extension (dilation), consistent with ongoing, thermal stress-driven subcriti-cal crack growth in the boulder. Our results therefore suggest that (1) insolation-related thermal stresses by themselves are of sufficient magnitude to facilitate incremental subcritical crack growth that can subsequently be exploited by other chemical and physical processes and (2) simple insolation can impart an elevated tensile stress field that makes rock more susceptible to cracking triggered by added stress from other weathering mechanisms. Our observed cracking activity does not correlate simply with environmental conditions, including temperature extremes or the often-cited 2 °C/min thermal shock threshold. We propose that this lack of correlation is due to both the ever-varying ambient stress levels in any rock at Earth's surface, as well as to the fact that ongoing subcritical crack growth itself will influence a rock's stress field and strength. Because similar thermal cycling is universally experienced by subaerially exposed rock, this study elucidates specific mechanisms by which solar-induced thermal stresses may influence virtually all weathering processes.

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In this paper, the material point method (MPM) is presented as a tool for simulating large deformation, gravity-driven landslides. The primary goal is to assess the interaction of these flow-like events with the built environment. This includes an evaluation of earthen mounds when energy dissipating devices are placed in the path of a snow avalanche. The effectiveness of the embankments is characterized using displacement, velocity, mass, and energy measures. A second example quantifies the force interaction between a landslide and a square rigid column. Multiple slide approach angles are considered, and various aspects of the impact force are discussed.

Recent biaxial experiments on spruce wood show that consideration of an elliptic failure surface according to Tsai and Wu, and of an elastic model for stress states within this envelope, gives an insufficient description of the mechanical behavior. As compression perpendicular to grain occurs, a nonlinear stress path results from a proportional biaxial strain path. Moreover, a phenomenological single-surface model does not permit easy identification of failure modes and thus renders the description of different post-failure mechanisms very difficult. Investigation of characteristic samples for various biaxial loading conditions enables the identification of four basic mechanisms covering the behavior of wood under plane stress conditions. The experimentally observed mechanical behavior will be described by means of a multi-surface plasticity model. It consists of four surfaces representing four basic failure modes. The first is a modified tension cut-off for the description of fiber rupture. The second is a mixed mode radial tension-shear model by Weihe applied to the perpendicular to grain direction. The third is an extension of the authors' prior model for perpendicular to grain compression, and the fourth surface covers the compressive failure parallel to grain. The model represents the orthotropic multi-surface elasto-plastic material clear wood. The aim of this paper is to present and discuss selected experimental data from biaxial tests with respect to distinct failure modes, and to develop an orthotropic plasticity model for its mathematical description. Since available experimental data cover only plane stress in the LR-plane, 1 both orthotropic failure and yield surfaces, respectively, are restricted to this case. IntroductionFrom the mechanical point of view, wood exhibits a pronounced orthotropic behavior with large ratios of mechanical properties such as Young's modulus or strength between the respective values parallel and transverse to the grain direction. Furthermore, it is well known that strength differs in tension and compression.Though a good amount of testing has been done for uniaxial states of stress, surprisingly little was known on the general effect of multiaxial states of stress on strength until the mid 1980s. The first remarkable experiments under mixed loading conditions were performed and reported by Spengler [26], Ehlbeck and Hemmer [10], and Hemmer [16]. Their experiments were restricted to small test specimens and to a restricted number of stress states. Spengler [26] investigated loading zones of beams. The specimen used was a small plate subjected to shear stress under superposed lateral compression. The results were restricted to the failure locations for this particular set of load cases. No deformation measurement has been performed.Ehlbeck and Hemmer [10], and Hemmer [16] used cylindrical pipes subjected to tension, torque, internal pressure, and combinations thereof. These experiments cover strength characteristics in the LT-plane. The deformation behavior has been reported...

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SUMMARYThis paper presents an investigation of strategies for handling dissipative phase interactions in the context of multi-field material point method formulations in which each phase is assigned its own motion. Different families of phase interaction strategies using both nodal and particle-based approaches are developed, and in particular, a new smoothed volume fraction approach is presented that can handle interaction effects in a general and consistent manner while reducing anomalous effects of phase boundaries and grid crossings. The effectiveness of this approach is demonstrated via convergence studies using a fundamental model problem.